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MATERNAL ANATOMY



External Genitalia



Vulva / Pudenda
Includes all structures from symphysis pubis to perineal body: mons pubis, labia
majora and minora, clitoris, hymen, vestibule, urethral opening, Bartholin glands,
minor vestibular glands and Skene glands
 Mons pubis

Fat-filled cushion overlying the symphysis pubis

After puberty, covered by hair that forms the escutcheon
 Labia majora

Embryologically homologous with the male scrotum

Vary in appearance depending on amount of fat contained

Continuous directly with the mons pubis superiorly

Round ligaments terminate at their upper borders

Posteriorly, taper and merge into the area overlying the perineal body
to form the posterior commissure

Hair covers the outer surface, but is absent on the inner surface

Aprocrine, eccrine and sebaceous glands are abundant

Beneath the skin, there is a dense connective tissue layer, which is
nearly void of muscular elements, but is rich in elastic fibers and
adipose tissue supplied with a rich venous plexus

During pregnancy, vasculature commonly develops varicosities from
increased venous pressure created by the enlarging uterus
 Labia minora

Thin tissue fold that lies medial to each labium majus

Male homologue is the ventral shaft of the penis

Extend superiorly, where each divides into two lamella; from each side,
the lower lamellae fuse to form the frenulum of the clitoris, and the
upper merge to form the prepuce

Inferiorly, extend to approach the midline as low ridges of tissue that
join to form the fourchette

Composed of connective tissue with numerous vessels, elastin fibers
and very few smooth muscle fibers

Supplied with many nerve endings and are extremely sensitive

Epithelia of the labia minora vary with location: thinly keratinized
stratified squamous epithelium on the outer surface, and
nonkeratinized squamous epithelium on the inner surface after the
demarcating Hart line

Lack hair follicles, eccrine glands and apocrine glands; there are many
sebaceous glands
 Clitoris

Principal female erogenous organ

Erectile homologue of the penis

Located beneath the prepuce, above the frenulum and urethra, and
projects downward and inward toward the vaginal opening
...
Glans is covered by
stratified squamous epithelium, and is richly innervated
...


Blood supply stems from branches of the internal pudendal artery:
deep artery of the clitoris supplies the clitoral body, whereas the dorsal
artery of the clitoris supplies the glans and prepuce
...


Perforated by six openings: the urethra, the vagina, two Bartholin gland
ducts, two Skene gland ducts

Posterior portion between the fourchette and vaginal opening is called
the fossa navicularis; usually observed only in nulliparas
 Hymen

Surrounds the vaginal opening

Composed mainly of elastic and collagenous connective tissue

Both outer and inner surfaces are covered by nonkeratinized stratified
squamous epithelium

Torn at several sites during the first coitus

In pregnant women, epithelium is thick and rich in glycogen

Changes produced by childbirth: transformation into several nodules
termed hymenal or myrtiform caruncles
 Vagina

Musculomembranous tube that extends to the uterus

Interposed lengthwise between the bladder and rectum

Anteriorly, separated from the bladder and urethra by connective tissue
(vesicovaginal septum)












Posteriorly, between the lower portion of the vagina and the rectum,
connective tissue forms the rectovaginal septum
...

Upper end is subdivided into anterior, posterior and two lateral fornices
by the cervix  of considerable importance since internal pelvic
organs can be palpated through the thin walls of these fornices;
posterior fornix provides surgical access to the peritoneal cavity
At the midportion, lateral walls are attached to the pelvis by visceral
connective tissue; attachments blend into the investing fascia of the
levator ani
Lining is composed of nonkeratinized stratified squamous epithelium
and underlying lamina propria
No vaginal glands; vagina is lubricated by a transudate originating from
the vaginal subepithelial capillary plexus and crosses the permeable
epithelium; secretions are notably increased during pregnancy due to
increased vascularity
Proximal portion supplied by the cervical branch of the uterine artery
and by the vaginal artery (which can arise from the uterine or inferior
vesical or directly from the internal iliac artery)
Middle rectal artery contributes supply to posterior vaginal wall; distal
walls receive contributions from the internal pudendal artery
Venous plexus surrounds the vagina and follows artery course
Lymphatics from the lower third, along with those of the vulva, drain
primarily into the inguinal lymph nodes
...
Those from the middle third drain into the
internal iliac nodes
...


Perineum
Boundaries mirror those of the bony pelvic outlet: pubic symphysis anteriorly,
ischiopubic rami and ischial tuberosities anterolaterally, sacrotuberous ligaments
posterolaterally, and coccyx posteriorly
Arbitrary line joining the ischial tuberosities divides the perineum into the anterior
(urogenital) triangle and the posterior (anal) triangle
Perineal body is a fibromuscular mass at the junction of both triangles; also called
the central tendon of the perineum; provides significant support and serves as the
junction for several structures superficially and deeply
Perineal body is incised by an episiotomy incision, and is torn with second to fourth
degree lacerations
...
Of these, the pubococcygeus / pubovisceral muscle is more
commonly damaged
Posterior triangle
 Contains the ischioanal fossae, anal canal and anal sphincter complex
(internal and external anal sphincters, puborectalis)
 Branches of the pudendal nerve and internal pudendal vessels are also
found here
 Pudendal nerve

Exits through the greater sciatic foramen at a level posterior to the
sacrospinous ligament and just medial to the ischial spine
...


As it courses behind the sacrospinous ligament and within the
pudendal canal, it is relatively fixed, and is thus at risk of stretch injury
during downward displacement of the pelvic floor during childbirth
Williams Obstetrics 24th Edition

Internal Generative Organs



Form the lateral boundaries of the pouch of Douglas

Uterus
Nonpregnant uterus is in the pelvic cavity between the bladder and rectum
Almost the entire posterior wall is covered by serosa (visceral peritoneum); lower
boundary of this periotoneum forms the anterior boundary of the pouch of Douglas
Only the upper portion of the anterior wall is so covered
...

Lower portion of the anterior uterine wall is united to the posterior wall of the
bladder by the vesicouterine space
...
Dissection caudally within this space lifts the
bladder off the lower uterine segment for hysterotomy and delivery
...
Also in this area are the origins of the round and uteroovarian
ligaments
...

Bulk of the uterine body, but not the cervix, is muscle
...

 Nulligravid uterus measures 6 to 9 cm in length compared with 9 to 10 cm in
multiparous women; averages 60 g and weighs more in parous women
Cervix:
 Upper boundary is the internal os, which corresponds to the level at which
the peritoneum is reflected up onto the bladder
 Upper cervical segment (portio supravaginalis) lies above the vagina’s
attachment to the cervix
...

 Lower cervical segment (portio vaginalis) protrudes into the vagina
...
After labor, it
is converted into a transverse slit divided into anterior and posterior lips
 Exterior to the external os is the ectocervix, lined by nonkeratinized stratified
squamous epithelium
 Endocervix is covered by a layer of mucin-secreting columnar epithelium
 During pregnancy, the endocervical epithelium moves out and onto the
ectocervix in the process of eversion
...
Cervical edema leads to softening
(Goodell sign), whereas isthmic softening is Hegar sign
...
Interlacing smooth muscle
fibers surround myometrial vessels and contract to compress these
...

 Amount of muscle diminishes progressively caudally
...
This layer is
divided into a functionalis layer (sloughed with menses) and a basalis layer,
which serves to regenerate the functionalis later
...
The cervicovaginal artery supplies blood
to the lower cervix and upper vagina
...

 A branch extends into the upper portion of each cervix, whereas numerous
other branches penetrate the uterine body to form the arcuate arteries
...
The spiral arteries supply the functionalis layer
...

 The straight arteries extend only into the basalis layer and are not responsive
to hormonal influences
...
Here it forms an anastomosis with the ovarian
branch of the uterine artery
...

This terminates in the ovarian vein
...

 Peritoneum that overlies the fallopian tube is termed the mesosalpinx, that
around the round ligament is the mesoteres, and that over the uteroovarian
ligament is the mesovarium
...

Cardinal ligament (transverse cervical ligament / Mackenrodt ligament)
 Thick base of the broad ligament
 United medially to the uterus and upper vagina
Uterosacral ligament
 Originates with a posterolateral attachment to the supravaginal portion of the
cervix and inserts into the fascia over the sacrum

Innervation
Sympathetic innervation to pelvic viscera begins with the superior hypogastric
plexus, also termed the presacral nerve
...

 At the level of the sacral promontory, this superior hypogastric plexus divides
into a right and left hypogastric nerve, which run downward along the pelvic
side walls
...
Their axons exit as part of the anterior rami of the spinal
nerves for those levels
...

Blending of the two hypogastric nerves and the two pelvic splanchnic nerves gives
rise to the inferior hypogastric plexus (pelvic plexus) at the level of S4/S5
...

Most afferent sensory fibers from the uterus ascend through the inferior hypogastric
plexus and enter the spinal cord via T10 through T12 and L1 spinal nerves
...

Sensory nerves from the cervix and upper part of the birth canal pass through the
pelvic splanchnic nerves to S2-S4
...


Lymphatics
Lymphatics from the cervix terminate mainly in the internal iliac nodes, which are
situated near the bifurcation of the common iliac vessels
...
5 to 5 cm in length, 1
...
6 to 1
...


Fallopian Tubes
Extend 8 to 14 cm from the uterine cornua and are anatomically classified along
their length as an interstitial portion, isthmus, ampulla and infundibulum
The extrauterine fallopian tube contains a mesosalpinx, myosalpinx and
endosalpinx
Supplied richly with elastic tissue, vessels and lymphatics
Sympathetic innervations of the tubes is extensive, in contrast to their
parasympathetic innervation
...

 Sensory afferents enter T10
...

 False pelvis

Above linea terminalis

Bounded posteriorly by lumbar vertebra and laterally by iliac fossa;
anteriorly by lower portion of anterior abdominal wall
 True pelvis

Below linea terminalis

Important in childbearing

Superior border: linea terminalis

Inferior margin: pelvic outlet

Posterior boundary: anterior surface of sacrum
o
Upper anterior margin corresponds to the promontory that may
be felt during bimanual pelvic examination in women with a small
pelvis; can provide a landmark for clinical pelvimetry
o
Straight line from promontory to sacrum tip measures 10 cm
o
Distance along the concavity averages 12 cm

Lateral limits: inner surface of isichial bones and the sacrosciatic
notches and ligaments
o
Extending from the middle of the posterior margin of each
ischium are the ischial spines; of great obstetrical importance:

Distance between them usually represents the shortest
diameter of the true pelvis

Landmarks in assessing the level to which the presenting
part of the fetus has descended into the true pelvis

Aid pudendal nerve block placement

Anterior: pubic bones, and the ascending superior rami of the ischial
bones, and the obturator foramina
Shapes
Caldwell-Moloy anatomical classification
Greatest transverse diameter of the inlet and its division into anterior and posterior
segments are used to classify the pelvis as gynecoid, anthropoid, android or
platypelloid
Posterior segment determines the type of pelvis, whereas the anterior segment
determines the tendency
Configuration of the gynecoid pelvis would intuitively seem suited for delivery of
most fetuses
Planes and Diameters
4 imaginary planes
 Plane of the pelvic inlet – superior strait
 Plane of the pelvic outlet – inferior strait
 Plane of the midpelvis – least pelvic dimensions
 Plane of greatest pelvic dimension – of no obstetrical significance
Pelvic Inlet
 Superior plane of the true pelvis
 During labor, fetal head engagement is defined by the fetal head’s biparietal
diameter passing through this plane

To aid this passage, the female pelvis is more nearly round than ovoid
...
Normally, this measures 10 cm or more, but cannot be
measured directly with the examining finger
...
5 to 2 cm from the diagonal
conjugate, which is determined by measuring the distance
from the lowest margin to the symphysis pubis to the
sacral promontory
...
5 cm
...
Lateral
boundaries are the sacrotuberous ligaments and the ischial
tuberosities

Anterior triangle is formed by the descending inferior rami of the pubic
bones
...


Clinically, 3 diameters of the pelvic outlet are described:
o
AP
o
Transverse
o
Posterior sagittal

Unless there is significant pelvic bony disease, pelvic outlet seldom
obstructs vaginal delivery

====================================================================
PHYSIOLOGY OF MENSTRUATION AND PREGNANCY
Ovarian Cycle
Follicular or Preovulatory Ovarian Phase
Only 400 follicles are normally released during female reproductive life
...

Follicular development has several stages, from gonadotropin-independent
recruitment of primordial follicle to growth to the antral stage
Although not required for early follicular maturation, FSH is required for further
development of large antral follicles
...
Only the follicles that progress to the selection window
develop the capacity to produce estrogen
...

 Rise in circulating FSH levels during the late luteal phase of the previous
cycle stimulates an increase in FSH receptors and the ability of aromatase
within granulosa cells to convert androstenedione into estradiol
...

Once LH receptors have appeared, the preovulatory granulosa cells begin to
secrete small quantities of progesterone
...

Williams Obstetrics 24th Edition

In addition, in late follicular phase, LH stimulates thecal cell production of
androstenedione, which is transferred to the adjacent follicles and aromatized
to estradiol
...

As the dominant follicle begins to grow, production of estradiol and the inhibins
increases and results in a decline of FSH
...



-

Ovulation
Onset of gonadotropin surge resulting from increasing estrogen secretion by
preovulatory follicles predicts ovulation
...

LH secretion peaks 10 to 12 hours before ovulation and stimulates resumption of
meiosis in the ovum and release of the first polar body
...

 During ECM synthesis, cumulus cells lose contact with one another and
move outward from the oocyte (expansion)
 Change in volume, along with LH-induced recomedeling of the ovariam ECM,
allows release of the mature oocyte
Luteal or Postovulatory Ovarian Phase
Corpus luteum develops from the dominant follicle (luteinization)
Basement membrane separating the granulosa lutein and theca lutein cells breaks
down, and by 2 days postovulation, blood vessels and capillaries invade the
granulosa cell layer
...

Hormone secretion patterns of the corpus luteum differ from that of the follicle
...
With pregnancy, the
corpus luteum continues progesterone production in response to hCG, which binds
to the same receptor as LH
...
The accompanying drop in estradiol and progesterone are
critical for follicular development and ovulation during the next ovarian cycle
...
Here there is proliferation of glandular, stromal and vascular endothelial
cells
...
These are dependent on tissue regrowth, which is estrogen-regulated
...

 Stromal cell proliferation appears to increase through paracrine and autocrine
functions of estrogen and increased local levels of FGF-9
 Estrogens also increase local production of VEHF, which causes
angiogenesis through vessel elongation in the basalis
By the late proliferative phase, the endometrium thickens from both glandular
hyperplasia and increased stromal ground substance (edema and proteinaceous
material)
...

 By day 17, glycogen accumulates in the basal portion of glandular epithelium,
creating subnuclear vacuoles and pseudostratification
...

 On day 18, vacuoles move to apical portion of secretory cells
...
Glandular cell mitosis ceases
...

 By mid to late secretory phase (days 22 to 25), there is predecidual
transformation of the upper 2/3 of the functionalis later
...

Secretory phase is also highlighted by the continuing growth and development of
the spiral arteries
 Morphological and functional properties are unique and essential for
establishing blood flow changes to permit either menstruation or implantation
...
Such rapid angiogenesis is
regulated through estrogen- and progesterone-regulated synthesis of VEGF
...
If progesterone secretion decreases with luteolysis, events leading to
menstruation are initiated
...

Anatomical events during menstruation:
 Marked changes in endometrial blood flow

With endometrial regression, spiral artery coiling becomes sufficiently
severe that resistance to blood flow increases strikingly, producing
endometrial hypoxia
...


Vasoconstriction precedes menstruation and is the most striking and
constant event observed in the cycle
...

====================================================================
FERTILIZATION
Fertilization
With ovulation, the secondary oocyte and adhered cells of the cumulus-oocyte
complex are freed from the ovary
...

Fertilization normally occurs in the oviduct, and must take place within a few hours,
and no more than a day after ovulation
...


Almost all pregnancies result when intercourse occurs during the 2
days preceding or on the day of ovulation
...
Fusion of the two nuclei and intermingling of maternal and paternal
chromosomes creates the zygote
...

As the lacunae form, a labyrinth is formed that is partitioned by these
cytotrophoblastic columns
...

Villi initially are located over the entire blastocyst surface
...

On the 12th day after fertilization, mesenchymal cords derived from extraembryonic
mesoderm invade the solid trophoblast columns
...

Once angiogenesis begins in the mesenchymal cores, tertiary villi are formed
...
The fetal-placental circulation is completed when the blood vessels of
the embryo are connected with the chorionic vessels
...
The most striking
exaggeration of this process is seen with hydatidiform mole
...

Williams Obstetrics 24th Edition

-

The definitive chorionic plate is formed by 8 to 10 weeks as the amnionic and
primary chorionic plate mesenchyme fuse together
...


Estrogen precursors (DHEA and DHEA-S)
Produced by fetal adrenal glands
Converted by the placenta into estrone and estradiol
====================================================================

====================================================================
EMBRYONIC AND FETAL DEVELOPMENT
PLACENTAL HORMONES
Human chorionic gonadotropin (hCG)
Biologic activity similar to LH
...

Produced almost exclusively by the placenta; low levels produced by fetal kidney
Best known function is the rescue and maintenance of corpus luteum function
(continued progesterone production)
Second role is stimulation of fetal testicular testosterone secretion, which is
maximum only when hCG levels peak
 At a critical time in male sexual differentiation, hCG enters fetal plasma from
the syncytiotrophoblast, and acts as an LH surrogate to stimulate Leydig cell
replication and testosterone synthesis to promote male sexual differentiation
...

Thus, pituitary LH secretion is minimal, and hCG acts as LH before this time
...

Other functions:
 Promotion of relaxin secretion by the corpus luteum
 Regulates expansion of uterine NK cell numbers during early stages of
placentation, ensuring appropriate establishment of pregnancy
Human placental lactogen (hPL)
Promotes maternal lipolysis with increased circulating FFA levels, providing an
energy source for maternal metabolism and fetal nutrition
...
To counterbalance the increased insulin resistance and prevent
maternal hyperglycemia, maternal insulin levels are increased by hPL
signaling on the prolactin receptor to increase maternal beta cell proliferation
...

Blastomeres continue to divide to form the morula
...

Accumulation of fluid between the morula cells leads to formation of the early
blastocyst
...

Blastocyst differentiates into the embryo-producing, five-cell inner cell mass, and
the remaining 53 cells form the placental trophoblast
...

 Primitive chorionic villi form, and this coincides with the expected day of
menses
...

During the 3rd week, fetal blood vessels in the chorionic villi appear
...
True circulation is
established, both within the embryo and between the embryo and the chorionic villi
...
At the end of the 4th week, the embro is 4 to 5 mm in length
...

Fetal Period
Transition from the embryonic period to the fetal period is arbitrarily designated to
begin 8 weeks after fertilization (10 weeks from the last menses)
...

12 weeks AOG
 Uterus is just palplable above the symphysis pubis
 Fetal CRL is 6 to 7 cm
 Centers of ossification have developed in most fetal bones, and the fingers
and toes have become differentiated
...

 External genitalia are beginning to show definitive signs of male or female
gender
...

16 weeks AOG
 CRL is 12 cm
 By 14 weeks, gender can be determined
 Eye movements begin at 16 to 18 weeks, coinciding with midbrain maturation
20 weeks AOG
 Midpoint of pregnancy
 From this point onwards, fetus moves about every minute and is active 10 to
30 percent of the time
 Fetal skin less transparent; lanugo covers its entire body; some scalp hair
 Cochlear function develops between 22 and 25 weeks, and its maturation
continues for six months until delivery
...

 Fetus born at this time will attempt to breathe, but many will die because the
terminal sacs, required for gas exchange, have not yet formed
...

28 weeks AOG
 CRL is 25 cm
 Thin skin is red and covered with vernix caseosa
 Papillary membrane has just disappeared from the eyes; isolated eye
blinking peaks during this time
 The otherwise normal neonate born at this age has a 90 percent chance of
survival without physical or neurological impairment
...

40 weeks AOG
 Considered term from the onset of the LMP
 Fetus now fully developed
 Average CRL of 36 cm

====================================================================
MATERNAL PHYSIOLOGY
Reproductive Tract
Uterus
In the nonpregnant woman, the uterus weighs 70 g, and is almost solid, except for
a cavity of 10 ml or less
...

 Total volume of contents at term averages 5 L
...

 At term, the organ weighs 1100 g
...

 Accompanying the increase in myocyte size is an accumulation of fibrous
tissue, particularly in the external muscle layer, together with an increase in
elastic tissue content
...

The walls of the corpus become considerably thicker during the first few months of
pregnancy, but begin to thin gradually
...

 In these later months, it is changed into a muscular sac with thin, soft, readily
indentable walls through which the fetus can be palpated
...
After 12 weeks,
however, the increase in size is related predominantly to pressure exerted by the
expanding products of conception
...

 In the later months of pregnancy, the attachments of the fallopian tubes,
round and ovarian ligaments are already near the middle of the uterus
...


Each cell in this layer has a double curve so that the interlacing of any
two gives approximately the form of a figure eight
...

Uterine contractility
 Beginning in early pregnancy, uterus undergoes irregular contractions that
are normally painless (Braxton-Hicks contractions)
...


Until the last several weeks of pregnancy, these are infrequent, but
their number increases during the last week or two (as often as every
10 to 20 minutes)

Late in pregnancy, these may cause some discomfort and account for
false labor
Uteroplacental blood flow
 Blood flow regulation

Maternal-placental blood flow progressively increases by means of
vasodilation
...


Downstream fall in vascular resistance leads to an acceleration of flow
velocity and shear stress in upstream vessels, which in turn leads to




circumferential vessel growth
...

Normal pregnancy is also characterized by vascular refractoriness to
the pressor effects of angiotensin II and norepinephrine
...

Relaxin may also help mediate uterine artery compliance
...

Rearrangement of the collagen-rich connective tissue, which is the major
component of the cervix, is necessary to permit functions such as maintenance of a
pregnancy to term, dilatation to aid delivery, and repair following parturition
...
This tissue tends to be red and velvety and
bleeds even with minor trauma, such as with Pap smear sampling
...

 At the onset of labor, this mucus plug is expelled resulting in a bloody show
...


In most pregnant women, as a result of progesterone, when cervical
mucus is spread and dried on a glass slide, it is characterized by poor
crystallization, or beading
...

Ovaries
Ovulation ceases during pregnancy, and maturation of new follicles is suspended
...

Fallopian Tubes
Musculature undergoes little hypertrophy during pregnancy
Epithelium of the tubal mucosa somewhat flattened
Vagina and Perineum
During pregnancy, increased vascularity and hyperemia develop in the skin and
muscles of the perineum and vulva, with softening of the underlying abundant
connective tissue
...

Vaginal walls undergo striking changes in preparation for the distention that
accompanies labor and delivery
 Increase in mucosal thickness
 Loosening of connective tissue
 Smooth muscle cell hypertrophy
 Papillae of the vaginal epithelium undergo hypertrophy to create a fine,
hobnailed appearance
Increased volume of cervical secretions within the vagina during pregnancy
consists of a thick, white discharge
...

Breasts
In the early weeks of pregnancy, women often experience breast tenderness and
paresthesias
...
The nipples become considerably larger, more deeply
pigmented and more erectile
...

The areolae become broader and more deeply pigmented
...

For most normal pregnancies, prepregnancy breast size and volume of milk
production do not correlate
...
These are called striae gravidarum or stretch marks
...
5 kg
...
5 L
...

Clearly demonstrable pitting edema of the ankles is seen in most pregnant women
at the end of the day
...

 At term, the fetus and placenta together weigh about 4 kg and contain 500
mg of protein, or about half of the total pregnancy increase
...

Amino acid concentrations are higher in the fetal than in the maternal compartment
...


-

Carbohydrate metabolism
Normal pregnancy is characterized by mild fasting hypoglycemia, postprandial
hyperglycemia, and hyperinsulinemia
 This is consistent with a pregnancy-induced state of peripheral insulin
resistance, the purpose of which is likely to ensure a sustained postprandial
supply of glucose to the fetus
...

Increased lipid synthesis and food intake contribute to maternal fat accumulation
during the first two trimesters
...

 This transition to a catabolic state favors maternal use of lipids as an energy
source and spares glucose and amino acids for the fetus
...

 TAG, VLDL, LDL and HDL are increased in the third trimester
 After delivery, levels decrease
...

Electrolyte and Mineral Metabolism
Sodium and potassium
 During normal pregnancy, nearly 1000 mEq of sodium and 300 mEq of
potassium are retained
...

 Although there are increased total accumulations of sodium and potassium,
their serum concentrations are decreased slightly because of expanded
plasma volume
...


-

This reduction follows lowered plasma albumin concentrations and, in
turn, a consequent decrease in the amount of circulating protein-bound
nonionized calcium
...


This demand is largely met by a doubling of maternal intestinal calcium
absorption mediated, in part, by Vitamin D

In addition, dietary intake of sufficient calcium is necessary to prevent
excess depletion from the mother
...
Both total and ionized magnesium
concentrations are lowered
...

Iodine
 Requirements increase during normal pregnancy

Maternal T4 production increases to maintain maternal euthryoidism
and to transfer thyroid hormone to the fetus early in gestation before
the fetal thyroid is functioning

Fetal thyroid hormone production increases during the second half of
pregnancy, contributing to increased maternal iodine requirements
because iodide readily crosses the placenta

Primary route of excretion is through the kidney; and with increased
GFR, there is increased excretion
Other minerals
 Pregnancy induces little change in metabolism of other minerals other than
their retention in amounts equivalent to those needed for growth
...
Expansion is most rapid
in the second trimester
...

Expansion results from an increase in both plasma and erythrocytes (more plasma
than erythrocytes)
 Moderate erythroid hyperplasia is present in the bone marrow, and the
reticulocyte count is elevated slightly
...
As a
result, whole blood viscosity decreases
...
0 g/dL, especially in late pregnancy, should be considered
abnormal and usually due to iron deficiency rather than pregnancy
hypervolemia
...


These are obligatory losses and accrue even when the mother is iron
deficient
 The average increase in the total circulating erythrocyte volume (450 ml)
requires another 500 mg
...


In most women, this amount is not available from iron stores
...

At the same time, fetal red cell production is not impaired because the
placenta transfers iron even if the mother has severe IDA
...


These normal losses are from the placental implantation site,
episiotomy or lacerations, and lochia
 On average, the mother loses 500 to 600 ml of predelivery whole blood
during vaginal delivery of a single fetus
...


Immunological functions
Pregnancy is both a pro-inflammatory and anti-inflammatory condition, depending
on the stage of gestation
...


During implantation and placentation, the blastocyst must break
through the uterine cavity epithelial lining to invade endometrial tissue
...

 Midpregnancy is anti-inflammatory

In this period of rapid fetal growth and development, the predominant
feature is induction of an anti-inflammatory state
...
This might be related to relaxinmediated impairment of neutrophil activation
...
This might be due to reappearance of leukocytes previously shunted
out of an active circulation
...


During the third trimester, there is an increase in granulocytes and CD8
T lymphocytes, along with a concomitant reduction in the percentages
of CD4 T lymphocytes and monocytes
 Circulating leukocytes undergo phenotypic changes including upregulation of
certain adhesion molecules
...
They are even more enhanced in
multifetal gestation
...

Clotting time, however, does not differ significantly
...

Cardiovascular system
Heart
As the diaphragm becomes progressively elevated, the heart is displaced to the left
and upward, and is rotated on its long axis
...

No characteristic ECG readings other than slight left-axis deviation due to altered
heart position

-

Many of the normal cardiac sounds are modified
Structurally, the increasing plasma volume seen during normal pregnancy is
reflected by enlarging cardiac end-systolic and end-diastolic dimensions
 No associated changes in septal thickness or in ejection fraction

This is because the dimensional changes are accentuated by
substantive ventricular remodeling, which is characterized by eccentric
left-ventricular mass expansion

Cardiac output
During normal pregnancy, mean arterial pressure and vascular resistance
decrease, while blood volume and basal metabolic rate increase
...
It continues to increase and remains elevated
during the remainder of pregnancy
...
Thus,
cardiac filling may be reduced and cardiac output diminished
...

During the first stage of labor, cardiac output increases moderately
...

The pregnancy-induced increase is lost after delivery, at times dependent on blood
loss
...

 Normal pregnancy is not a continuous “high-output” state
Circulation and blood pressure
Changes in posture affect arterial blood pressure
...

Arterial pressure decreases to a nadir at 24 to 26 weeks and rises thereafter
...

Antecubital venous pressure remains unchanged during pregnancy
...

 Venous blood flow in the legs is retarded during pregnancy except when the
lateral recumbent position is assumed
...
They also
predispose to DVT
...
This also leads to lower uterine blood flow, potentially affecting fetal heart
rate patterns
...

 Renin produced by both the maternal kidney and the placenta
 Increased angiotensionogen production by maternal and fetal liver due to
increased estrogen production (important in first trimester blood pressure
maintenance)
Development of refractory vascular reactivity to angiotensin II due to progesterone
Cardiac natriuretic peptides
Secreted in response to chamber-wall stretching
Regulate blood volume by promoting natriuresis, dieresis and vascular smooth
muscle relaxation
ANP and BNP levels maintained at nonpregnant range despite increased plasma
volume
 ANP-induced physiological adaptations participate in extracellular fluid
volume expansion and in the increased plasma aldosterone concentration
characteristic of normal pregnancy
Prostaglandins
Increased prostaglandin production during pregnancy has a central role in control of
vascular tone, blood pressure and sodium balance
 Renal medullary PGE2 synthesis increased in late pregnancy; probably
natriurteic
 PGI2, the principal prostaglandin of endothelium, also increased in late
pregnancy; implicated in the development of angiotensin resistance in
pregnancy
...
Vascular sensitivity to it is not
Williams Obstetrics 24th Edition

altered during normal pregnancy
...


-

Nitric oxide
Potent vasodilator released by endothelial cells with important implications for
modifying vascular resistance during pregnancy
One of the most important mediators of placental vascular tone and development
Abnormal NO synthesis has been linked to preeclampsia development
Respiratory Tract
Diaphragm rises about 4 cm during pregnancy
Subcostal angle widens appreciably as the transverse diameter of the thoracic cage
lengthens approximately 2 cm
Thoracic circumference increases about 6 cm, but not sufficiently to prevent
reduced residual lung volumes created by the elevated diaphragm
Even so, a diaphragmatic excursion is greater in pregnant than in nonpregnant
women
...

 Increased minute ventilation is due to enhanced respiratory drive secondary
to the stimulatory action of progesterone, low expiratory reserve volume, and
compensated respiratory alkalosis
...
Consequently, maternal
arteriovenous oxygen difference is decreased
...

During labor, oxygen consumption increases even more
...


This is offset because the slight pH increase also stimulates an
increase in 2,3-DPG in maternal erythrocytes, which shifts the curve
back to the right
...

Urinary system
Kidney
Kidney size increases
Both GFR and renal plasma flow increase early in pregnancy
...

 This change may be mediated by relaxin, which increases endothelin and
nitric oxide production in the renal circulation
...
Late in pregnancy, urinary flow and
sodium excretion averages less than half the excretion rate in the supine position
compared with that in the lateral recumbent position
...
Amino acids and water-soluble vitamins are excreted in much greater
amounts
...
7 to
0
...
Values of 0
...

Creatinine clearance is higher in pregnancy
...

Hematuria is often the result of contamination during collection
...

 Also common after difficult labor and delivery because of trauma to the
bladder and urethra
Because of hyperfiltration in pregnancy, the threshold for defining proteinuria
increases to at least 300 mg/day
...
Above this level,
increased intraureteral tonus results, with resultant dilatation of the ureters
...

Bladder
Few significant anatomical changes in the bladder before 12 weeks
From that time onward, however, increased uterine size, the hyperemia that affects
all pelvic organs, and the hyperplasia of bladder muscle and connective tissue
elevate the trigone and cause thickening of its posterior intraureteric margin
...

No mucosal changes other than an increase in the size and tortuosity of its blood
vessels
...

Toward the end of pregnancy, particularly in nulliparas in whom the presenting part
often engages before labor, the entire base of the bladder is pushed forward and
upward, converting the normal convex surface into a concavity
...

Gastrointestinal tract
Gums may become hyperemic and softened, and may bleed when mildly
traumatized (pregnancy gingivitis)
...

Heartburn is common during pregnancy and is most likely caused by reflux of acidic
secretions into the lower esophagus
...

Gastric emptying time appears to be unchanged during each trimester
...

 As a result, one danger of general anesthesia for delivery is regurgitation and
aspiration of either food-laden or highly acidic gastric contents
...
They are caused in large measure by
constipation and elevated pressure in veins below the level of the enlarged uterus
...

Serum albumin concentration decreases
...
Serum
globulin levels are also slightly higher
...


Gallbladder
Contractility is reduced, and leads to increased residual volume
...



-

Endocrine system
Pituitary gland
Pituitary gland enlarges, primarily due to estrogen-stimulated hypertrophy and
hyperplasia of the lactotrophs
Gonadotrophs decline in number, and corticotrophs and thyrotrophs remain
constant
...

Maternal pituitary gland is not essential for pregnancy
...

 As early as 8 weeks AOG, GH secreted from the placenta is detectable
 By 17 weeks, the placenta is the principal source of GH secretion
 Placental GH, which differs from pituitary GH by 13 amino acid residues, is
secreted by syncytiotrophoblast in a nonpulsatile fashion
...


Maternal serum levels correlate positively with birthweight, and
negatively with fetal-growth restriction and uterine artery resistance

Fetal growth still progresses in the complete absence of this hormone
Prolactin:
 Maternal plasma levels increase markedly during normal pregnancy
 Paradoxically, plasma concentrations decrease after delivery even in women
who are breast feeding
...

 Principal function of maternal prolactin is to ensure lactation
...


Increases the number of estrogen and prolactin receptors in these cells

Promotes mammary alveolar cell RNA synthesis, galactopoiesis and
production of casein, lactalbumin, lactose and lipids
Oxytocin and ADH
 Quiescence of oxytocin systems during pregnancy
 Levels of ADH do not change during pregnancy
Thryoid gland
Increased production of thyroid hormones to meet maternal and fetal needs
Undergoes enlargement caused by glandular hyperplasia and increased vascularity
 Enlargement is not pathological, but normal pregnancy does not typically
cause significant thyromegaly
...

Early in the first trimester, levels of TBG increase (due to increased synthesis in the
liver secondary to estrogen stimulation)
...

Free serum T4 levels rise slightly and peak along with hCG levels, and then return
to normal
...

 TRH levels are not increased during normal pregnancy
...

Normal suppression of TSH during pregnancy may lead to a misdiagnosis of
subclinical hyperthyroidism
...

Iodine status
 Iodine requirements increase during normal pregnancy
...

Parathyroid glands
Regulation of calcium concentration is closely interrelated with magnesium,
phosphate and parathyroid hormone, vitamin D and calcitonin physiology
...


Increased calcium absorption during early pregnancy despite low PTH
levels (the normal stimulus for active vitamin D production)
...


Calcitonin
 Oppose the actions of PTH and vitamin D to protect maternal skeletal
calcification during times of calcium stress
...

 Calcium and magnesium increase the biosynthesis and secretion of
calcitonin, as do various gastric hormones
...

 Serum concentration of circulating cortisol is increased, but much of it is
bound by transcortin, the cortisol-binding globulin
...
But as
pregnancy progresses, ACTH and free cortisol levels paradoxically rise
equally and strikingly
...
At the same time, levels of
renin and angiotensin II substrate normally are increased, especially during
the latter half of pregnancy
...

Deoxycorticosterone
 Maternal plasma levels progressively increase during pregnancy
...

 Levels are higher in fetal blood, which suggests transfer of fetal
deoxycorticosterone into the maternal compartment
...

 Both are converted to estradiol in the placenta, increasing clearance
 Conversely, increased plasma sex hormone-binding globulin in pregnant
women retards testosterone clearance
...

Interestingly, little or no testosterone in maternal plasma enters the fetal circulation
as testosterone
...

Musculoskeletal system
Progressive lordosis to compensate for anterior position of the enlarging uterus
...

Sacroiliac, sacrococcygeal and pubic joints have increased mobility
...
It may contribute to maternal
posture alterations and in turn create low back discomfort
...

Central nervous system
Memory
Changes in the CNS are relatively few and mostly subtle
...

Studies show that mean blood flow in the middle and posterior cerebral arteries
decreases in pregnancy
...

Corneal sensitivity is decreased, and the greatest changes are late in gestation
...

Greatest disruption of sleep is encountered postpartum and may contribute to
postpartum blues or to frank depression

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