Maternal and Fetal Health
INTRODUCTION TO MATERNITY NURSING
Providing
care to childbearing families is aimed at the ideal of having every pregnancy
result in a healthy mother, baby, and family unit. The nurse today faces many
evolving and challenging issues in achieving this goal. Such advances as in
vitro fertilization and embryo freezing have afforded people opportunities once
never thought possible. An increasing number of high-risk pregnancies result
from such factors as drug abuse, acquired immunodeficiency syndrome, late or no
prenatal care, teenage pregnancies, and pregnancies in women older than age 35.
Technologic advances in high-risk obstetric units, fetal
monitoring, sonography, and neonatal intensive care
units are now providing the means to improve maternal health and save fetuses and infants who would not have survived years ago.
Today's childbearing families
have many options. The planned birth may take place in the traditional hospital
setting, a birthing center, or at home. The primary
care provider may be a physician, a certified nurse-midwife, or a lay midwife.
Birth-related choices commonly include the use of labor,
delivery, and recovery rooms or labor, delivery,
recovery, and postpartum rooms; various birthing positions and analgesic methods;
alternative pain relief strategies such as hydrotherapy; and the decision to
allow children and others to be present during labor
and delivery. Regionalization of obstetric services has provided childbearing
families with access to the technologic advances and skilled personnel capable
of managing pregnancy or neonatal complications.
Economic changes in the health
care climate have dramatically affected the practice of nursing as
cost-containment considerations have shortened the hospital length of stay.
Many
hospitals have adopted a practice of 12- to 24-hour discharge after delivery
coordinated with home health care follow-up.
This combination of advancing
technology, pregnancy risk factors, and changing economics challenges the nurse
to be a highly skilled clinician and outstanding communicator.
TERMINOLOGY USED IN MATERNITY NURSING
- Gestation—pregnancy or maternal condition
of having a developing fetus in the body.
- Embryo—human conceptus
up to the 10th week of gestation (8th week postconception).
- Fetus—human conceptus from 10th week of gestation (8th week postconception) until delivery.
- Viability—capability of living, usually
accepted as 24 weeks, although survival is rare.
- Gravida (G)—woman
who is or has been pregnant, regardless of pregnancy outcome.
- Nulligravida—woman
who is not now and never has been pregnant.
- Primigravida—woman
pregnant for the first time.
- Multigravida—woman
who has been pregnant more than once.
- Para (P)—refers to past pregnancies
that have reached viability.
- Nullipara—woman
who has never completed a pregnancy to the period of viability. The woman
may or may not have experienced an abortion.
- Primipara—woman
who has completed one pregnancy to the period of viability regardless of
the number of infants delivered and regardless of the infant being live or
stillborn.
- Multipara—woman
who has completed two or more pregnancies to the stage of viability.
- Living children—refers
to the number of living children a woman has delivered regardless of
whether they were live births or stillborn births.
A woman who is pregnant for
the first time is a primigravida and is described as Gravida 1 Para 0 (or G1P0). A woman who delivered one fetus carried to the period of viability and who ispregnant again is described as Gravida
2,
OBSTETRIC
HISTORY
TPAL
In
some obstetric services, a woman's obstetric history is summarized by a series
of four digits, such as 5-0-2-5. These digits correspond with the abbreviation TPAL.
- T—represents
full-term deliveries, 37 completed weeks or more.
- P—represents
preterm deliveries, 20 to less than 37 completed weeks.
- A—represents
abortions, elective or spontaneous loss (miscarriage) of a pregnancy
before the period of viability.
- L—epresents the number of children living. If a child
has died, further explanation is needed for clarification.
If, for example, a particular
woman's history is summarized as G 7, P 5-0-2-5, then she has been pregnant
seven times, had five term deliveries, zero preterm deliveries, two abortions,
and five living children.
GTPALM
In
some institutions, a woman's obstetric history can also be summarized as
GTPALM.
- G—represents gravida.
- T—represents
full-term deliveries, 37 completed weeks or more.
- P—represents
preterm deliveries, 20 to less than 37 completed weeks.
- A—represents
abortions, elective or spontaneous loss of a pregnancy before the period
of viability.
- L—represents
the number of children living. If a child has died, further explanation is
needed for clarification.
- M—represents
the number of multiple gestations and births (not the number of neonates
delivered).
If, for example, a particular
woman's history is summarized as G 5, P 5-0-0-6-1, then she has been pregnant
five times, had five term deliveries, zero preterm deliveries, zero abortions,
six living children, and one multiple gestation/birth.
THE EXPECTANT MOTHER
MANIFESTATIONS OF PREGNANCY
Pregnancy
may be determined by cessation of menses, enlargement of the uterus, and a
positive result on a pregnancy test. These and the many other manifestations of
pregnancy are classified into three groups: presumptive, probable, and
positive.
Presumptive
Signs and Symptoms
Physical signs and symptoms that suggest, but do not
prove, pregnancy.
- Abrupt cessation of menses—pregnancy
is suspected if more than 10 days have elapsed since the time of the
expected onset in a healthy woman who previously had predictable menstrual
periods.
- Breast
changes:
- Breasts enlarge and become tender. Veins in
breasts become increasingly visible.
- Nipples become larger and more pigmented.
Nipple tingling may also be present.
- Colostrum, a thin, milky fluid, may be expressed in the second half of
pregnancy.
- Skin
pigmentation changes:
- Chloasma/melasma gravidarum (the mask of pregnancy)—brownish
pigmentation appearing on the face in a butterfly pattern in 50% to 70%
of women. It is usually symmetric and is distributed on the forehead,
cheeks, and nose. The mask of pregnancy is more common in dark-haired,
brown-eyed women and is progressive throughout the pregnancy.
- Linea nigra—dark vertical line on the
abdomen between the sternum and the symphysis
pubis.
- Abdominal striae
(striae gravidarum)—reddish
or purplish linear marks sometimes appearing on the breasts, abdomen,
buttocks, and thighs because of the stretching, rupture, and atrophy of
the deep connective tissue of the skin.
- Nausea and vomiting (morning sickness)—occurs
mainly in the morning but may occur at any time of the day, lasting a few
hours. Begins between 2 and 6 weeks after conception and usually
disappears spontaneously near the end of the first trimester (12 weeks).
- Frequency
of urination:
- Caused by pressure of the expanding uterus
on the bladder
- Decreases when the uterus rises out of the
pelvis (around 12 weeks)
- Reappears when the fetal
head engages in the pelvis at the end of pregnancy
- Fatigue—characteristic of early
pregnancy in response to increased hormonal levels.
Probable Signs and Symptoms
Objective
findings detected by 12 to 16 weeks of gestation.
- Enlargement of abdomen—at
about 12 weeks' gestation, the uterus can be felt through the abdominal
wall, just above the symphysis pubis.
- Changes in shape, size, and consistency of
the uterus:
- Uterus enlarges, elongates, and decreases
in thickness as pregnancy progresses. The uterus changes from a pear
shape to a globe shape.
- Hegar's sign—lower uterine segment softens 6 to 8 weeks after the onset of the
last menstrual period.
- Changes
in cervix:
- Chadwick's sign—bluish
or purplish discoloration of cervix and vaginal wall
- Goodell's sign—softening of the cervix; may occur as early as 4 weeks.
- With inflammation and carcinoma during
pregnancy, the cervix may remain firm.
- Intermittent contractions of the uterus
(Braxton Hicks contractions)—painless, palpable
contractions occurring at irregular intervals, more frequently felt after
28 weeks. They
usually disappear with walking or exercise.
- Ballottement—sinking and rebounding of the fetus in its surrounding amniotic fluid in response to
a sudden tap on the uterus (occurs near midpregnancy).
- Changes in levels of human chorionic gonadotropin (hCG) in maternal plasma and
urine.
- Leukorrhea—increase
in vaginal discharge.
- Quickening (sensations of fetal movement in the abdomen)—occurs between the
16th and 20th week after the onset of the last menses.
- Positive hCG—laboratory
(urine or serum) test for pregnancy.
Positive Signs and Symptoms
Diagnostic of
pregnancy.
- Fetal heart tones (FHTs)—usually heard
between 16th and 20th week of gestation with a fetoscope
or the 10th and 12th week of gestation with a Doppler stethoscope.
- Fetal movements felt by the examiner (after about 20 weeks' gestation).
- Outlining of the fetal
body through the maternal abdomen in the second half of pregnancy.
- Sonographic evidence (after 4 weeks' gestation) using vaginal ultrasound. Fetal cardiac motion can be
detected by 6 weeks' gestation.
MATERNAL PHYSIOLOGY DURING PREGNANCY
Duration of Pregnancy
- Averages 280 days or 40 weeks (10 lunar
months; 9 calendar months) from the 1st day of the last normal menstrual
period.
- Duration may also be divided into three
equal parts, or trimesters, of slightly more than 13 weeks or 3 calendar
months each.
- Estimated date of confinement is calculated
by adding 7 days to the date of the 1st day of the last menstrual period
and counting back 3 months (Nägele's
rule).
- For example, if a woman's last menstrual
period (LMP) began on September 10, 1999, her estimated date of
confinement (EDC) would be September 10, 1999, plus 7 days = September
17, 1999, minus 3 months = June 17, 1999. If the date of the woman's LMP
begins after March 31, an additional year must be added to give a correct
EDC. Thus, an additional year would be added to the above date making the
correct EDC = June 17, 2000.
- Another method of calculating the EDC is
McDonald's rule: after 24 weeks' gestation, the fundal
height measurement will correspond to the week of gestation plus 2 to 4
weeks.
Changes in the Reproductive Tract
Uterus
- Enlargement during pregnancy involves
stretching and marked hypertrophy of existing muscle cells secondary to
increased estrogen and progesterone levels.
- In addition to an increase in the size of
the uterine muscle cells, there is an increase in fibrous tissue and
elastic tissue. The size and number of blood vessels and lymphatics increase.
- Enlargement and thickening of the uterine
wall are most marked in the fundus.
- By the end of the third month (12 weeks),
the uterus is too large to be contained wholly within the pelvic cavity—it can
now be palpated suprapubically.
- As the uterus rises out of the pelvis, it
rotates somewhat to the right because of the presence of the rectosigmoid colon on the left side of the pelvis.
- By 20 weeks' gestation, the fundus has reached the level of the umbilicus.
- By 36 weeks, the fundus
has reached the xiphoid process.
- By the end of the fifth month, the myometrium hypertrophy ends and the walls of uterus
become thinner, allowing palpation of the fetus.
- During the last 3 weeks, the uterus descends
slightly because of fetal descent into the
pelvis.
- Changes in contractility occur—from
the first trimester, irregular painless contractions occur (Braxton Hicks
contractions). In latter weeks of pregnancy, these contractions become
stronger and more regular.
- There is a progressive increase in uteroplacental blood flow during pregnancy.
Cervix
- Pronounced softening and cyanosis—due to
increased vascularity, edema,
hypertrophy, and hyperplasia of the cervical glands.
- Endocervical glands secrete thick mucus that forms a cervical plug and
obstructs the cervical canal. This plug prevents bacteria and other
substances from entering and ascending into the uterus.
- Erosions of cervix, common during pregnancy,
represent an extension of proliferating endocervical
glands and columnar endocervical epithelium.
- Evidence of Chadwick's sign,
the bluish, purplish coloring of the cervix.
This sign is due to the increased vascularity
and hyperemia caused by increased estrogen levels.
Ovaries
- Ovulation ceases during pregnancy;
maturation of new follicles is suspended.
- One corpus luteum
functions during early pregnancy (first 10 to 12 weeks), producing mainly
progesterone. However, small levels of estrogen
and relaxin are also produced by the corpus luteum.
- After 8 weeks' gestation, the corpus luteum remains the source for the hormone relaxin. However, relaxin is
not required for a successful pregnancy outcome and normal delivery.
Vagina and Outlet
- Increased vascularity,
hyperemia, and softening of connective tissue in
skin and muscles of the perineum and vulva.
- Vaginal walls prepare for labor: mucosa increases in thickness, connective
tissue loosens, and small-muscle cells hypertrophy. Secretions are thick,
white, and acidic in nature and play a major role in the prevention of
infections.
- Vaginal secretions increase; pH is 3.5 to 6—because
of increased production of lactic acid from glycogen in the vaginal
epithelium by Lactobacillus acidophilus. (Acid pH
probably aids in keeping vagina relatively free of pathogenic bacteria.)
- Hypertrophy of the structures, along with
fat deposits, causes the labia majora to close
and cover the vaginal introitus (vaginal
opening).
Changes in the Abdominal Wall
- Striae gravidarum (stretch marks) may develop—reddish,
slightly depressed streaks in the skin of abdomen, breast, and thighs
(become glistening silvery lines after pregnancy).
- Linea nigra may form—line of
dark pigment extending from the umbilicus down the midline to the symphysis. Commonly during the first pregnancy, the linea nigra occurs at the
height of the uterus. During subsequent pregnancies, the entire line may
be present early in gestation.
- Diastasis recti may occur as muscles (rectus) separate. If severe, a part of the anterior
uterine wall may be covered by only a layer of skin, fascia, and
peritoneum.
Breast Changes
- Tenderness and tingling occur in early weeks
of pregnancy.
- Increase in size by second month—hypertrophy
of mammary alveoli. Veins become more prominent, and striae
may develop as the breasts enlarge.
- Nipples become larger, more deeply
pigmented, and more erectile early in pregnancy.
- Colostrum, a yellow secretion rich in antibodies, may be expressed by second
trimester.
- Areolae become broader and more deeply pigmented. The depth of
pigmentation varies with the person's complexion.
- Scattered through the areola are a number of
small elevations (glands of
Metabolic
Changes
Numerous
and intensive changes occur in response to rapidly growing fetus
and placenta.
Weight gain
average
25
to 35 lb (11.5 to 16 kg)
|
TABLE 36-1 Components of
Weight Gain |
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Water metabolism
- The average woman retains 6 to 8 L of extra
water during the pregnancy due to hormonal influence.
- Approximately 4 to 6 L of fluid cross into the extracellular
spaces. This
creates a physiologic increase in blood volume (hypervolemia).
- Many pregnant women experience a normal
accumulation of fluid in their legs and ankles at the end of the day. This
is most common in the third trimester and is referred to as physiologic edema.
- Sodium excretion in the normal pregnant
woman is similar to the nonpregnant woman.
- Sodium retention is usually directly
proportional to the amount of water accumulated during the pregnancy.
However, pregnancy lends itself toward sodium depletion, making sodium
regulation more difficult.
- Additional sodium is required during
pregnancy to meet the need for increased intravascular and extracellular fluid volumes and to maintain a
normal isotonic state.
NURSING ALERT
The limitation of sodium is discouraged in pregnancy
because it can result in decreased kidney function, resulting in decreased
urine output. As a result, the pregnancy outcome could also be adversely
affected.
Protein Metabolism
- The fetus, uterus,
and maternal blood are rich in protein rather than in fat or
carbohydrates.
- At term, fetus and
placenta contain 500 g of protein or approximately half of the total
protein increase of pregnancy.
- Approximately 500 g more of protein is added
to the uterus, breasts, and maternal blood in the form of hemoglobin and plasma proteins.
Carbohydrate Metabolism
- Carbohydrate metabolism during pregnancy is
controlled by glucose levels in the plasma and the metabolism of glucose
in the cells.
- The liver controls the plasma glucose level.
Not only does it store glucose as glycogen, but it also converts it into
glucose when the woman's blood glucose levels are low.
- Early in pregnancy, the effects of estrogen and progesterone can induce a state of hyperinsulinemia. As pregnancy advances, there is
increased tissue resistance coupled with increased hyperinsulinemia.
- Approximately 2% to 3% of all women will
develop gestational diabetes mellitus during pregnancy regardless if they
have a history of carbohydrate intolerance.
- Pregnant women with preexisting
diabetes mellitus (type 1 or 2) may experience a worsening of the disease
attributed to hormonal changes occurring with pregnancy.
- During pregnancy, there is a “sparing” of
glucose used by maternal tissues and a shunting of glucose to the placenta
for use by the fetus.
- Human placental lactogen
(placental hormone) promotes lipolysis,
increases plasma free fatty acids, and thereby provides alternative fuel
sources for the mother.
- Human placental lactogen,
estrogen, progesterone, and cortisol
oppose the action of insulin during pregnancy and promote maternal lipolysis as well.
Fat Metabolism
- Lipid metabolism during pregnancy causes an
accumulation of fat stores, mostly cholesterol, phospholipids, and
triglycerides.
- This accumulation of fat stores has no
negligible effect on the fetus.
- Fat storage occurs before the 30th week of
gestation. After 30 weeks' gestation, there is no further fat storage,
only fat mobilization that correlates with the increased utilization of
glucose and amino acids by the fetus.
- The ratio of low-density proteins to
high-density proteins is increased during pregnancy.
Nutrient Requirements
Caloric Requirements
- Additional calories are usually not required
during the first trimester due to the limited metabolic demands.
- An additional 300 kcal/dL
are required during the second and third trimester over the nonpregnant woman. However, due to the variety of
women and their individualized needs, the exact caloric requirements need
to be established on an individual basis.
- Caloric expenditure varies throughout
pregnancy. There is a slight increase in early pregnancy and a sharp
increase near the end of the first trimester, continuing throughout pregnancy.
Protein Requirements
- Protein is required for adequate amino acids
to accommodate the normal development of the fetus,
blood volume expansion, and growth of maternal breast and uterine tissue.
- An additional requirement of 10 g of protein
per day is recommended over the nonpregnant
intake.
Carbohydrate and Fat Requirements
- As in the nonpregnant
woman, carbohydrates should supply 55% to 60% of calories in the diet and
should be in the form of complex carbohydrates, such as whole-grain cereal
products, starchy vegetables, and legumes.
- Fat intake should not exceed 30% of the
diet. Saturated fats should not exceed 10% of the total calories.
Iron Requirements
- Total circulating red blood cells (RBCs) increase about 40% to 50% during pregnancy;
therefore, iron requirements are increased to 20 to 40 mg daily. This usually exceeds dietary
intake.
- Supplemental iron is valuable and necessary
during pregnancy and for several weeks after pregnancy or lactation.
- During the last half of pregnancy, iron is
transferred to the fetus and stored in the fetal liver. This store lasts 3 to 6 months.
Changes in the
Cardiovascular System
Heart
- Diaphragm is progressively elevated during pregnancy; heart is
displaced to the left and upward, with the apex moved laterally.
- Heart sounds—exaggerated splitting of the first heart sound; a loud, easily
heard third sound.
- Heart murmurs—systolic murmurs are common and usually disappear after delivery.
Blood Volume Changes
- Cardiac volume increases by 40% to 50% (1,450 to 1,750 mL) by 32 weeks' gestation, causing slight hypertrophy
of the heart and increased cardiac output.
- Cardiac output increases by 30% to 50% above normal within the
first 13 weeks of pregnancy and reaches a volume of 6 to 7 L/minute by
term.
- In the supine position, the large uterus compresses the venous
return from the lower half of the body to the heart. This may cause
arterial hypotension, referred to as the supine hypotensive syndrome. Cardiac output increases
by 25% to 30% with an increase in uterine and renal blood flow when the
woman turns from her back to lateral position (either left or right side).
- Femoral venous pressure increases—because of slowing of blood
flow from lower extremities as a result of pressure of enlarged uterus on
pelvic veins and inferior vena cava.
- Increased cutaneous blood flow dissipates
excess heat caused by increased metabolism of pregnancy.
- Plasma volume increases 20% to 30% (250 to 450 mL),
resulting in hemodilution, more commonly
referred to as physiologic anemia
of pregnancy or physiologic dilutional
anemia. This “anemic” state is not a true pathologic state and does decrease the risk of
thrombosis.
Blood Pressure Changes
- Blood pressure—during the first half of pregnancy, there is a
slight (5 to 10 mm Hg) decrease in systolic and diastolic blood pressure,
with the lowest point occurring in the second trimester. By the third
trimester, the blood pressure gradually returns to prepregnancy
levels.
- Maternal position influences blood pressure: the highest reading is
obtained in the sitting position, the lowest reading is obtained in the
left lateral position, and an intermediate reading is obtained in the
supine position.
- Maternal blood pressure will also rise with uterine contractions
and returns to the baseline level after the uterine
contraction is over.
Hematologic Changes
- Total volume of circulating RBCs
increases 18% to 30%; hemoglobin concentration
at term averages 12 to 16 g/dL; hematocrit concentration at term averages 37% to 47%.
- Average leukocyte (WBC) count in the third trimester is 5 to
12,000/ml. WBC count can be elevated as high as 25,000 or more during labor—cause unknown; probably represents the
reappearance in the circulation of leukocytes previously shunted out of
active circulation.
- Pregnancy is a hypercoagulable state due
to the increased levels of a number of essential coagulation factors.
These factors include factor I (fibrinogen by 50%), factor V (proaccelerin or labile factor), factor VII (proconvertin or serum prothrombin
conversion accelerator), factor VIII (antihemophilic
factor or antihemophilic globulin), factor IX
(plasma thromboplastin component or Christmas
factor), factor X (Stuart or Prower factor), and
factor XII (Hageman or glass or contact factor). Factor II (prothrombin) increases slightly, whereas factors XI
(plasma thromboplastin antecedent) and XIII
(fibrin-stabilizing factor) decrease during pregnancy.
- There is no significant change in the number, appearance, or
function of platelets. Average platelet count is 140,000 to 400,000/mm3,
which increases the risk to the pregnant woman for venous thrombosis.
Changes in the Respiratory Tract
- Diaphragm is elevated during pregnancy—chiefly
by the enlarging uterus that decreases the length of the lungs.
- Thoracic cage expands its anteroposterior
diameter causing flaring of the ribs—result of increased mobility of
rib attachments.
- Breathing is more diaphragmatic than costal.
- Hyperventilation occurs—increase in respiratory rate,
tidal volume (amount of air inspired and expired with normal breath)
increases 30% to 40%, and minute ventilation (amount of air inspired in 1
minute) increases 40%.
- Increased total volume lowers blood partial pressure of carbon
dioxide (Pco2), causing mild respiratory alkalosis that is
compensated for by lowering of the bicarbonate concentration.
- Increased respiratory rate and reduced Pco2 are probably
induced by progesterone and estrogen to a lesser
degree on the respiratory center.
- Oxygen consumption increases 15% to 20% and as much as 300% in labor. This increase leads to increased maternal
alveolar and arterial oxygen partial pressure levels.
- Approximately 60% to 70% of pregnant women experience shortness of
breath; the cause is unknown.
- Nasal stuffiness and epistaxis
(nosebleeds) are also common during pregnancy, secondary to vascular
congestion caused from the increased estrogen
levels.
Changes in Renal System
- Ureters become
dilated and elongated during pregnancy because of mechanical pressure and
perhaps due to the effects of progesterone. When the uterus rises out of
the uterine cavity, it rests on the ureters,
compressing them at the pelvic brim. Dilation is greater on the right side—the
left side is cushioned by the sigmoid colon.
- Glomerular
filtration rate (GFR) increases 50% by the second trimester, and the
increase persists almost to term. Renal plasma flow increases early in
pregnancy and decreases to nonpregnant levels in
the third trimester. These changes may be due to placental lactogen.
- Glucosuria may be
evident because of the increase in glomerular
filtration without an increase in tubular resorptive
capacity for filtered glucose.
- Excreted protein may be increased due to the increased GFR, but is
not considered abnormal until the level exceeds 250 mg/dL.
Slight amounts of protein may be excreted during or just after vigorous labor.
- Toward the end of pregnancy, pressure of the presenting part
impedes drainage of blood and lymph from the bladder base, typically
leaving the area edematous, easily traumatized,
and more susceptible to infection.
Changes in GI Tract
- Gums may become hyperemic and softened
and may bleed easily.
- A localized vascular swelling of the gums may appear—called epulis of
pregnancy.
- Stomach and intestines are displaced upward and laterally by the
enlarging uterus. Heartburn (pyrosis) is common,
caused by reflux of acid secretions in the lower esophagus.
- Tone and motility of GI tract decrease, leading to prolongation of
gastric emptying due to the large amount of progesterone produced by the
placenta. Decreased motility, mechanical obstruction by the fetus, and decreased water absorption from the colon
leads to constipation.
- Hemorrhoids are
common because of elevated pressure in veins below the level of the large
uterus and constipation.
- Distention and hypotonia of the gallbladder are
common, which can cause stasis of bile. Additionally, there is a decrease
in emptying time and thickening of bile, resulting in hypercholesterolemia
and gallstone formation.
- Liver function tests are altered. With pregnancy, bilirubin, aspartate aminotransferase, and alanine
aminotransferase values are unchanged; prothrombin time may show a slight increase or be
unchanged. Liver
size and morphology are unchanged.
- Peptic ulcer formation or exacerbation is uncommon during pregnancy
due to decreased hydrochloric acid (caused by increased estrogen levels).
- The appendix is pushed superiorly.
Changes in the Endocrine System
- Anterior pituitary gland enlarges slightly; posterior pituitary
gland remains unchanged.
- Thyroid is moderately enlarged because of hyperplasia of glandular
tissue and increased vascularity.
- Basal metabolic rate increases progressively during normal
pregnancy (as much as 25%) because of metabolic activity of fetus.
- Level of protein-bound iodine and thyroxine
rises sharply and is maintained until after delivery because of increased
circulatory estrogen and hCG.
- Hyperthyroidism during pregnancy is rare.
- Parathyroid gland size and concentration of parathyroid hormone
increase and peak between 15 and 35 weeks' gestation.
- Adrenal secretions considerably increased—amounts
of aldosterone increase as early as the 15th
week to accommodate for the increased sodium excretion.
- Pancreas—because of the fetal glucose needs for
growth, there are alterations in maternal insulin production and usage.
- Estrogen,
progesterone, cortisol, and human placental lactogen (hPL) decrease the
maternal utilization of glucose.
- Cortisol also
increases maternal insulin production.
- Insulinase, an
enzyme produced by the placenta, deactivates maternal insulin.
- These changes result in an increased need for insulin, and the
islets of Langerhans increase their production
of insulin.
Changes in Integumentary System
- Pigment changes occur because of melanocyte-stimulating
hormone, the level of which is elevated from the 2nd month of pregnancy
until term.
- Striae gravidarum appear in later months of pregnancy as
reddish, slightly depressed streaks in the skin of the abdomen and
occasionally over the breasts and thighs.
- A brownish-black line of pigment is usually formed in the midline
of the abdominal skin—known as linea nigra.
- Brownish patches of pigment may form on the face—known
as chloasma/melasma or “mask of
pregnancy.”
- Angiomas
(vascular spider nevis),
minute red elevations commonly on the skin of the face, neck, upper chest,
legs, and arms, may develop.
- Reddening of the palms (palmar erythema) may also occur.
- There is also an increased warmth to the
skin and increased nail growth.
Changes in the Musculoskeletal System
- The increasing mobility of sacroiliac, sacrococcygeal,
and pelvic joints during pregnancy is a result of hormonal changes,
specifically the hormone relaxin.
- The center of gravity shifts secondary to
increased weight gain, fluid retention, lordosis,
and mobile ligaments. This mobility and the change in the center of gravity contribute to alteration of maternal
posture and to back pain.
- Late in pregnancy, aching, numbness, and weakness in the upper
extremities may occur because of lordosis and paresthesia, which ultimately produces traction on the
ulnar and median nerves.
- Separation of the rectus muscles due to
pressure of the growing uterus creates a diastasis recti. If
this is severe, a portion of the anterior uterine wall is covered by only
a layer of skin, fascia, and peritoneum.
Changes in the Neurologic System
- Usually no system changes.
- Mild frontal headaches are common in the first and second trimester
and are usually related to tension or hormonal changes.
- Dizziness is common and is related to vasomotor instability,
postural hypotension, or hypoglycemia following
long periods of standing or sitting.
- Tingling sensations in the hands are common and are due to
excessive hyperventilation, which decreases maternal Pco2
levels.
- Severe headaches that occur after 20 weeks' gestation and are
accompanied by visual changes, elevated blood pressure, proteinuria, and facial edema
should be evaluated immediately.
Steroid Hormones
- Estrogen:
- Is secreted by the ovaries in early
pregnancy, but by 7 weeks' gestation over half of the estrogen
is secreted by the placenta.
- The three classic estrogens during
pregnancy are estrone, estradiol,
and estriol. More than 90% of the estrogen secreted during pregnancy is estriol.
- Estrogens also ensure uterine growth and
development, maintenance of uterine elasticity and contractility,
·
- maintenance of breast growth and its ductal
structures, and enlargement of the external genitalia.
- Progesterone:
- Is initially secreted by the corpus luteum and later by the placenta.
- Plays a critical role in the maintenance of
the pregnancy by suppressing the maternal immunologic response to the fetus and the rejection of the trophoblasts.
- Progesterone also helps to maintain the endometrium, inhibits uterine contractility, helps in
the development of breast lobules for lactation, stimulates the maternal
respiratory center, and relaxes smooth muscle.
Placental Protein Hormones
- hCG:
- Secreted by the syncytiotrophoblasts
and stimulates the production by the corpus luteum
of progesterone and estrogen until the fully
developed placenta takes over.
- In multiple gestations, hCG can be twice as high as in a single
pregnancy.
- hCG levels peak around 10 weeks'
gestation (50,000 to 100,000 mIU/mL) then
decrease to 10,000 to 20,000 mIU/mL by 20
weeks' gestation.
- hPL:
- Also referred to as human
chorionic somatomammotropin.
Produced by the syncytiotrophoblasts of the
placenta; detected in maternal serum as early as 6 weeks' gestation.
- Serum hPL levels
rise concomitantly with placental growth.
- hPL is an antagonist of insulin.
It increases the amount of free fatty acids available to the fetus for metabolic needs and decreases the maternal
metabolism of glucose allowing for protein synthesis. This action allows
the fetus to have the needed nutrients when the
woman has not or is not eating.
Other Hormones
- Prostaglandins:
- Exact function is still unknown.
- Affect smooth muscle contractility and some
potent vasodilators.
- Essential for the cardiovascular adaptation
to pregnancy, cervical ripening, and initiation of labor.
- Increased levels of prostaglandins may lead
to vasodilatation.
- Relaxin:
- Secreted primarily by the corpus luteum. Can be secreted in small amounts by the decidua and the placenta.
- Inhibits uterine activity, decreases the
strength of uterine contractions, softens the cervix, and remodels
collagen.
- Prolactin:
- Released from the anterior pituitary gland.
- Responsible for sustaining milk protein,
casein, fatty acids, lactose, and the volume of milk secretion during
lactation.
Structure
of the Pelvis
Bones
of the Pelvis
The
pelvis is composed of four bones:
- Two innominate
bones (hip bones) form the sides and front.
- Sacrum and coccyx form the back. Pelvic
bones are held together by fibrocartilage of the
symphysis pubis and several ligaments.
Divisions of the Pelvis
- False pelvis—lies above an imaginary line
called the linea terminalis or pelvic brim (see Figure 36-1).
Function of the false pelvis is to support the enlarged uterus.
- True pelvis lies below the pelvic brim or linea terminalis; it is the
bony canal through which the fetus must pass. It
is divided into three planes: the inlet, the midpelvis,
and the outlet.
- Inlet:
§
Upper boundary of the true pelvis—bounded by
upper margin of symphysis pubis in front, linea terminalis on sides, and
sacral promontory (first sacral vertebra) in back.
§
Largest diameter of inlet is
transverse
§
Smallest diameter of inlet is anteroposterior.
§
Anteroposterior
diameter is most important diameter of inlet: measured clinically by diagonal
conjugate—distance
from lower margin of symphysis to the sacral
promontory (usually 5½
inches [14 cm])
§
Obstetric (true) conjugate—distance
between inner surface of symphysis and sacral
promontory measured by subtracting ½ to ¾ inch (1.5 to 2 cm) (thickness of symphysis) from the diagonal conjugate. Adequate diameter
is usually 11.5 cm. This is the shortest anteroposterior
diameter through which the fetus must pass.
- Midpelvis:
§
Bounded by inlet above and outlet
below—true
bony cavity. Contains the narrowest portion of the pelvis.
§
Diameters cannot be measured
clinically.
§
Clinical evaluation of adequacy is
made by noting the ischial spines. Prominent spines
that protrude into the cavity indicate a contracted midpelvic
space. The interspinous
diameter is 4 inches (10 cm).
- Outlet:
§
Lowest boundary of the true pelvis.
§
Bounded by lower margin of symphysis in front, ischial tuberosities on sides, tip of sacrum posteriorly.
§
Most important diameter clinically is
distance between the tuberosities (> 4 inches).
Shapes of the
Pelvis
There
are four main types of pelvic shapes
- Gynecoid (normal female pelvis); optimal diameters in all three planes; 50%
of all women.
- Android (normal male pelvis); posterior
segments are decreased in all three planes; deep transverse arrest of
descent of the fetus and failure of rotation of
the fetus are common; 20% of all women.
- Anthropoid (apelike pelvis with long anteroposterior diameter); may allow for easy delivery
of an occiput-posterior presentation of the fetus; 25% of all women.
- Platypelloid (flat female pelvis with wide transverse diameter); arrest of fetal descent at the pelvic inlet is common; labor progress can be poor; 5% of all women.
Structure of the Uterus
- Located behind the symphysis
pubis between the bladder and the rectum.
- Uterine size increases after childbirth.
- Consists
of four parts:
- Fundus—upper
rounded segment that extends above the insertion of the fallopian tubes; fetal growth is measured by fundal
height.
- Body (corpus)—main portion
between cervix and fundus.
- Isthmus (neck)—lower uterine
segment.
- Cervix—divided into two sections:
- Supravaginal—portion
that extends inside the uterus; contains internal os
that opens into the uterine cavity.
- Vaginal—portion that extends outside
the uterus into the vagina; contains the external os
that is the visible opening of the cervix; portion that is felt during
vaginal examination in assessing cervical dilatation.
- Consists
of three layers:
- Parietal peritoneum—serous
coat; covers most of uterus except cervix and anterior portion of body.
- Myometrium—three
layers:
- Outer layer rovides power
to expel the fetus.
- Middle layer—provides contractions
after childbirth to control blood loss.
- Inner layer—provides sphincter
action to help keep cervix closed during pregnancy.
- Endometrium—highly
vascular mucous membrane; responds to hormonal stimulation with
hypertrophy and secretion; sloughs if pregnancy does not occur.