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PATHOPHYSIOLOGY OF THE PLACENTA
153
10. What is relaxin, and where is it produced?
Relaxin is produced in several sites including the corpus luteum, the decidua, the atria of the
heart, and the placenta. It appears to have a broad range of activities and to play a role in
collagen remodeling, although it does not seem to be necessary for pregnancy maintenance or
normal delivery.
11. What are the physical measurements of a normal placenta?
A human placenta weighs between 450 and 550 g, with an average diameter of 20 cm and an aver-
age thickness of 2.5 cm.
12. Can placental thickness be measured antenatally?
Yes. Placental thickness can be easily measured by ultrasound examination. Conditions such as
intrauterine fetal infections, diabetes mellitus, and immune and nonimmune hydrops are associated
with abnormally thick placentas (>4 cm).
13. What is a battledore placenta?
Insertion of the umbilical cord at the margin of the placenta—also referred to as a marginal cord
insertion. It is found in 7% of pregnant women, and its incidence is higher in multifetal gestations. It
has no known clinical significance.
14. What is a velamentous cord insertion?
When the umbilical cord does not insert directly into the placenta; instead, it separates into vessels
that run through the fetal membranes immediately adjacent to the placenta. This occurs in 1% of
singleton pregnancies. Vasa previa is a rare but serious condition in which fetal blood vessels are
positioned over the internal os. Because the blood vessels are not protected by Wharton jelly, they can
tear during labor and result in fetal exsanguination.
15. What is placenta previa?
A condition in which the placenta covers the internal os. For more information on this topic, see
Chapter 66.
16. What are placenta accreta, increta, and percreta?
Placenta accreta is the term used when the placental villi are attached to the myometrium as
a result of partial or complete absence of the decidua basalis and the Nitabuch layer. Placental
increta occurs when placental villi invade the myometrium. When villi invade through the myome-
trium, the condition is known as placenta percreta. For more information on these topics, see
Chapter 66.
17. What is placental abruption?
Separation of a normally implanted placenta before the birth of the fetus. For more information on this
topic, see Chapter 66.
18. What is a succenturiate placenta?
A succenturiate placenta, or succenturiate placental lobe, is a condition in which an extra lobe of the
placenta separated from it by space and connected to it by vessels. If unrecognized, this lobe may be
retained at the time of delivery and cause postpartum bleeding and infection.
19. What are the different types of placentation in twin pregnancy?
The three different types are dichorionic-diamniotic, monochorionic-diamniotic, and
monochorionic-monoamniotic.
20. Why is it important to know the chorionicity in twin gestations?
Perinatal mortality is highest for monochorionic-monoamniotic twins, and monochorionic-diamniotic
twins are at increased risk for selective growth restriction and twin-to-twin transfusion syndrome
(TTTS). For more information on this topic, see Chapter 60.
21. What is the significance of a single umbilical artery?
Normally, three umbilical vessels are present: two arteries and one vein. The incidence of single
umbilical artery (SUA) is approximately 1% of all singleton births. SUA has been associated with an
increased rate of additional fetal malformations, most commonly in the renal, cardiovascular, gastro-
intestinal, and central nervous systems. If an additional abnormality is found, the risk of chromosomal
abnormalities is increased.
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B
iBliography
1. Benirschke K. Twinning. In: Knobil E, Neill JD, eds. Encyclopedia of Reproduction. vol. 4. San Diego: Academic Press;
1998:887–891.
2. Benirschke K. Normal development. In: Creasy R, Resnik R, Iams JD, Lockwood CJ, Moore TR, eds. Creasy and Resnik’s
Maternal-Fetal Medicine: Principles and Practice. 7th ed. Philadelphia: Saunders; 2014.
3. Heifetz SA. The umbilical cord: obstetrically important lesions. Clin Obstet Gynecol. 1996;39:571–587.
4. Hull AD. Placenta previa, placenta accreta, abruptio placentae, and vasa previa. In: Creasy R, Resnik R, Iams
JD, Lockwood CJ, Moore TR, eds. Creasy and Resnik’s Maternal-Fetal Medicine: Principles and Practice. 7th ed.
Philadelphia: Saunders; 2014.
5. Liu JH, Rebar RW. Endocrinology of pregnancy. In: Creasy R, Resnik R, Iams JD, Lockwood CJ, Moore TR, eds. Creasy
and Resnik’s Maternal-Fetal Medicine: Principles and Practice. 7th ed. Philadelphia: Saunders; 2014.
KEY POINTS: PATHOPHYSIOLOGY OF THE PLACENTA
1. Implantation occurs 6 days after fertilization, after which trophoblastic cells differentiate into inner
cytotrophoblasts and outer syncytiotrophoblasts.
2. The placenta functions as both a transport organ and an endocrine organ.
3. hCG is a glycoprotein made by the syncytiotrophoblast that serves to maintain progesterone
production by the corpus luteum in early pregnancy. Peak concentration occurs at 8 to 10 weeks of
gestation.
4. A velamentous cord insertion is when the umbilical cord inserts into the fetal membranes instead of
the placental disk; vasa previa is when the exposed vessels lie over the internal os.
5. Normally the umbilical cord contains three vessels: two arteries and one vein. SUA is associated
with an increased risk of additional malformations.
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1. Why is preconception counseling important?
Preconception counseling offers the opportunity to:
• Screen for and treat medical issues that place the mother and fetus at risk
• Optimize chronic medical and psychological diseases before conception
• Screen for substance or medication use that may be teratogenic
• Screen for genetic disorders in high-risk populations
• Educate patients on the importance of folic acid before and throughout pregnancy
• Review the patient’s obstetric history and discuss the risk of subsequent pregnancies
• Assess immunization status and administer appropriate vaccines before conception
• Evaluate for domestic violence, environmental exposures, and nutritional status
• Refer the patient to subspecialists for further counseling when appropriate
2. What relatively common medical conditions should be identified and addressed
during preconception counseling?
• Diabetes mellitus: This is associated with an increased risk of birth defects that is further
increased with poor glycemic control. Optimal blood glucose control, assessed by glycosylated
hemoglobin (HbA1c), should be achieved before conception. The presence of end-organ damage
should prompt referral to a subspecialist.
• Seizures: Effort should be made to achieve good control with monotherapy. Many antiepileptics are
teratogenic and should be avoided if at all possible (e.g., valproic acid, phenytoin). Adjustment of
antiepileptic medication should be done in conjunction with a neurologist.
• Hypertension: Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers
(ARBs) are teratogenic and should be discontinued. Hypertension in pregnancy is associated with
several pregnancy complications; for more information, see Chapter 49.
3. What congenital defect can be potentially averted by preconception counseling?
Neural tube defects (NTDs). Supplementation with 0.4 mg folic acid on a daily basis reduces the risk
of NTDs by 50%. Ideally, this regimen should be started a minimum of 1 month before conception.
For women with a history of an earlier child with an NTD, 4 mg folic acid per day can reduce the
recurrence rate by 72%. Women taking valproic acid or carbamazepine should also increase the daily
dose of folic acid to 4 mg.
4. What should women with phenylketonuria (PKU) be told before conception to
minimize risk to their unborn children?
Women with PKU must follow a phenylalanine-restricted diet before conception. Otherwise,
elevated phenylalanine levels can cause mental retardation, microcephaly, and cardiac defects
(see Chapter 36).
5. What laboratory tests may be indicated in preconception counseling?
• Complete blood count (CBC): can screen for hemoglobinopathies and anemia
• Hepatitis B antigen, rubella, and varicella titers: nonimmune women should be vaccinated before
pregnancy
• Screening for human immunodeficiency virus (HIV) and other sexually transmitted diseases
• Screening for specific genetic disorders, guided by family history and ethnic background
• Papanicolaou smear
• Diabetes screening in high-risk women
6. What conditions should prompt cardiac testing (e.g., electrocardiogram,
echocardiogram) before pregnancy?
• Pregestational diabetes
• Chronic hypertension (>10 years, or >40 years of age)
• Congenital heart disease
CHAPTER 35
PRECONCEPTION COUNSELING
Anna Karina Celaya, MD
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GENERAL OBSTETRICS
7. How should the family history be assessed?
Women should be asked whether they or their partners have any relatives with recognized genetic
disorders, congenital defects (e.g., NTD, cardiac anomaly, cleft lip or palate), or chromosomal
abnormalities. A first-degree family member with mental retardation of unknown cause should initiate
screening for fragile X syndrome.
8. What are the risks associated with advanced maternal age (≥35 years)
in pregnancy?
Approximately 10% of pregnancies occur among women of advanced maternal age. These pregnancies
have higher rates of fetal growth restriction, aneuploidy, spontaneous abortion, preeclampsia, gestational
diabetes, and medically indicated preterm delivery.
9. Do any absolute contraindications to pregnancy exist?
Yes. Because of extremely high mortality rates, women with Eisenmenger syndrome, pulmonary
hypertension, or a history of peripartum cardiomyopathy without recovery of cardiac function are
advised not to become pregnant. Women with Marfan syndrome who have aortic root dilation larger
than 4 cm also fall into this category.
B
iBliography
1. American College of Obstetricians and Gynecologists. The importance of preconception care in the continuum of
women’s health care. ACOG committee opinion no. 313. Obstet Gynecol. 2005;106:665–666.
2. American College of Obstetricians and Gynecologists. Moderate caffeine consumption during pregnancy. ACOG committee
opinion no. 462. Obstet Gynecol. 2010;116:467–468.
3. American College of Obstetricians and Gynecologists. Smoking cessation during pregnancy. ACOG committee opinion
no. 471. Obstet Gynecol. 2010;116:1241–1244.
4. American College of Obstetricians and Gynecologists. At-risk drinking and alcohol dependence: obstetric and
gynecologic implications. ACOG committee opinion no. 496. Obstet Gynecol. 2011;118:383–388.
5. Cunningham FG, Leveno KJ, Bloom SL, Spong CY, Dashe JS, Hoffman BL, Casey BM, Sheffield JS. Williams Obstetrics.
24th ed. New York: McGraw-Hill Medical; 2014.
6. Institute of Medicine. National Academy of Sciences. Fetal Alcohol Syndrome: Diagnosis, Epidemiology, Prevention and
Treatment. Washington, DC: National Academies Press; 1996.
KEY POINTS: PRECONCEPTION COUNSELING
1. Preconception counseling provides an important opportunity to identify and address any health
problems that may adversely affect a woman or her unborn child, or both.
2. Taken at least a month before conception, 0.4 mg folic acid on a daily basis reduces the risk of
NTDs by as much as 50%. Women at high risk or who have already had a pregnancy with this
complication are recommended to take 4 mg daily.
3. Pregnancy is not recommended for women with certain cardiac and pulmonary conditions.
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1. What does prenatal care encompass?
Prenatal care is the careful, systematic assessment and follow-up of a pregnant patient to ensure
the best possible health of the mother and her fetus. It is a preventive service and has been shown
to be beneficial and cost effective; women receiving no or inadequate prenatal care have far more
complications and poorer outcomes of pregnancy. Goals are threefold:
1. To prevent, identify, or ameliorate maternal or fetal abnormalities that adversely affect pregnancy
outcome, including socioeconomic and emotional factors, as well as medical and obstetric factors.
2. To educate the patient about pregnancy, labor and delivery, and parenting in addition to ways she
can improve her overall health.
3. To promote adequate psychological support from her partner, family, and caregivers so she can
successfully adapt to the pregnancy and the challenges of raising a family.
Prenatal care commences with an extensive initial history and physical examination. Estimated
gestational age and estimated date of delivery (EDD) are determined, and routine laboratory tests
are drawn. In subsequent visits the physician explores any problems, documents fetal growth, and
identifies potential complications. Assessment for risk factors is done at the initial visit and on each
subsequent appointment. Weight gain and nutritional well-being are frequently evaluated, and patient
education is provided on a timely basis.
2. How often should patients be seen?
The American College of Obstetricians and Gynecologists (ACOG) recommends that pregnant women
be seen for an extensive initial visit in early pregnancy and then every 4 weeks until 28 weeks, every
2 to 3 weeks to 36 weeks, and then weekly until delivery. For low-risk pregnancies, a national panel
has suggested seven visits total for parous women (at 6 to 8, 14 to 16, 24 to 28, 32, 36, 39, and
41 weeks) and nine visits for nulliparous (two additional visits at 10 to 12 and 40 weeks). For high-risk
patients, the schedule should be individualized and usually requires more visits.
3. What historical information should be recorded at the initial prenatal visit?
• Medical: Many chronic medical conditions have an effect, often adverse, on pregnancy outcome;
conversely, pregnancy usually has a distinct effect on the course of the condition itself.
• Surgical: Be sure to note any earlier surgical or anesthetic complications and need for blood
transfusion.
• Obstetric or gynecologic: Some events in the patient’s obstetric history often recur in subsequent
pregnancies (e.g., fetal or neonatal death, low birth weight, preterm delivery, preeclampsia or hyperten-
sion, and postpartum hemorrhage). A history of recent infertility treatment, pelvic inflammatory disease,
or ectopic pregnancy is also important for identifying early pregnancy complications such as tubal
pregnancy or multiple gestations. A history of past sexually transmitted diseases should also be taken.
• Family history: The history should focus on family members and relatives with cerebral palsy,
mental retardation, neural tube defects, and other congenital malformations, as well as specific
conditions such as cystic fibrosis, muscular dystrophy, and hemophilia. Inherited diseases are
important to ask about because increasing numbers are amenable to prenatal diagnosis.
• Social: Psychosocial background and lifestyle are also important because they frequently affect
pregnancy and neonatal outcome. Be sure to ask about smoking, use of alcohol and illicit drugs,
use of prescription and over-the-counter medications, employment and type of occupation, and the
existence of problems at home such as domestic violence.
4. What history elements should be obtained at subsequent prenatal visits?
A brief interval history should always be obtained, as well as a review of systems. Every patient
should be asked about pain, contractions or cramping, pelvic pressure, bleeding, discharge, dysuria,
CHAPTER 36
COMPREHENSIVE
PRENATAL CARE
Hai-Lang Duong, MD
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gastrointestinal problems, presence and adequacy of fetal movements, and whether any other prob-
lems have arisen since the last visit. Smokers should be asked about their progress in smoking cessa-
tion. Patients with medical conditions or known complications should be asked specific questions
regarding those problems.
5. What physical examination components should be performed at an initial
prenatal visit?
A general physical examination should always be performed at the first visit; this examination may be
the only one for many women over a several-year period. Principal examination components include
measurement of blood pressure and weight, heart and lung auscultation, palpation of the abdomen,
and a breast examination.
A routine pelvic examination can detect abnormalities of the vulva, vagina, cervix, uterus, and
adnexa. It is important to estimate the size of the early gravid uterus in weeks and assess the cervix.
A Papanicolaou (Pap) smear and cultures for sexually transmitted infections should be obtained, as well
as evaluation of any abnormal vaginal discharge. Traditionally, clinical pelvimetry has been performed to
determine pelvic adequacy in first pregnancies and for multiparous women who have experienced previ-
ous abnormal labor or difficult delivery. The only true test for pelvic adequacy, however, is a trial of labor.
6. Which laboratory tests should be ordered at an initial prenatal visit?
The number of laboratory tested considered “routine” has increased with time, and these tests are
listed in Table 36-1. Additional tests can be ordered as appropriate for women with health conditions.
7. How is gestational age determined?
An accurate last menstrual period (LMP) should be recorded at the first prenatal visit, along with the
woman’s normal menstrual cycle length and recent use of oral contraceptives. Careful determina-
tion of the EDD is needed so that therapeutic decisions at each stage of pregnancy are appropriately
made. The EDD is initially calculated using the Naegele rule: take the first day of the LMP, add 7 days
and 1 year, then subtract 3 months. This assumes that a term gestation is 280 days or 40 weeks from
the start of the LMP, however, and that menstruation occurs every 28 days. Variations in cycle length
and the timing of ovulation, use of oral contraception in the month preceding the LMP, and the appear-
ance of menstrual-like bleeding during early pregnancy can render estimated dates of conception
calculated with the method inaccurate.
Ultrasound measurement of the embryo or fetus in the first trimester (<14 and 0/7 weeks of
gestation) is the most accurate method of confirming the EDD based on LMP or giving a new EDD.
A crown-rump length (CRL) is used to assess the gestational age in the first trimester; in the second
and third trimesters, a collection of measurements known as biometrics (head circumference, bipari-
etal diameter, abdominal circumference, and femur length) is used. If a significant discrepancy exists
Table 36-1. Prenatal Laboratory Tests
INITIAL VISIT LATER IN PREGNANCY
Complete blood count
Urinalysis and culture
Blood type
Antibody screen
Serologic test for syphilis
Rubella immunity
Hepatitis B surface antigen
HIV testing
Papanicolaou smear
Gonorrhea and Chlamydia testing*
Tuberculosis screening*
Hemoglobin electrophoresis
†
Wet prep
†
Aneuploidy screening
Dipstick urine analysis (every visit)
Complete blood count (third trimester)
Gestational diabetes screening (24-28 weeks)
Group B streptococcus culture (36-37 weeks)
Antibody screening test (28 weeks; Rh-negative
patients)
HIV, Human immunodeficiency virus.
*In at-risk patients.
†
As needed.
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between an EDD based on ultrasound measurements and the EDD based on an LMP, the ultrasound
results should be used. Ultrasound dating is also used when the LMP is unknown. For more informa-
tion on ultrasound in pregnancy, see Chapter 38.
8. What physical examination components are important on subsequent prenatal visits?
Weight and blood pressure should always be recorded, and fetal heart rate should be assessed. The
fundal height is measured in centimeters from the symphysis pubis to the top of the uterus. In a
patient with a normal body habitus, serial measurements over the course of pregnancy provide an
excellent assessment of fetal growth. Between 18 and 34 weeks, the height in centimeters roughly
approximates the gestational week. Abnormal measurements should prompt a fetal ultrasound exami-
nation. Other examinations, including vaginal, are done as indicated by the patient’s interval history.
In the third trimester, Leopold maneuvers should be used to assess fetal position and estimate
fetal size. These maneuvers involve palpation of the uterus to determine the following:
• What fetal part lies in the fundus?
• On which side is the fetal back?
• What fetal part is oriented toward the pelvis, and is it engaged?
• How far has the fetal presenting part descended into the pelvis?
9. Why are a patient’s prepregnancy weight and weight gain during pregnancy
important?
Women who are underweight or who have poor weight gain during pregnancy are at increased risk for
fetal growth restriction, and a statistically significant relationship exists between poor maternal weight
gain and preterm delivery. Excessive weight gain during pregnancy can lead to a large for gestational
age (LGA) fetus, and prepregnancy obesity is associated with increased rates of spontaneous abortion,
congenital anomalies, gestational diabetes mellitus, intrauterine fetal death, hypertensive disorders of
pregnancy, cesarean delivery, thromboembolism, and postoperative wound infections.
For more information on nutrition in pregnancy and recommended weight gain based on mater-
nal body mass index, see Chapter 37.
10. How is a complete blood count useful during pregnancy?
Delivery is associated with a blood loss of 500 to 1000 mL; to avoid requiring a blood transfusion,
patients who are anemic need to be identified well ahead of delivery. Most cases of anemia in preg-
nancy result from iron deficiency and improve with 60 to 100 mg/day of oral elemental iron supple-
mentation. Microcytic anemia in the absence of iron deficiency should prompt testing for hereditary
anemias (see later). A platelet count can identify women with thrombocytopenia and, in severe cases,
prompt referrals to subspecialists.
11. How are urinalysis and urine culture useful during pregnancy?
All patients should have a urine sample collected on the first visit for urinalysis and urine culture.
Detection of the approximately 5% of patients with asymptomatic bacteriuria can prevent progression
to pyelonephritis, and women with group B streptococcus (GBS) bacteriuria can be identified (see later).
12. What is the importance of the blood type and antibody screening tests?
Rh-negative women must be identified so that they can be given Rh immune globulin (RhoGAM) at 28
to 30 weeks and within 72 hours of delivery to prevent Rh sensitization. The antibody screening test
is done to detect any antibodies (e.g., Rh, Kell, Duffy, Lewis) that have the potential to cause hemolytic
disease in the fetus and newborn infant. For more information on this topic, see Chapter 46.
13. Are Pap smears interpreted any differently in pregnant women?
No. Abnormal results should be managed according to guidelines published by the American Society
for Colposcopy and Cervical Pathology (ASCCP). If colposcopy is indicated, endocervical curettage is
not performed during pregnancy. For more information on this topic, see Chapter 27.
14. How is hemoglobin electrophoresis useful during pregnancy?
Sickle cell trait is estimated to be present in 8.5% of African Americans, and screening with hemoglo-
bin electrophoresis should be performed. Women who carry the trait are more susceptible to urinary
tract infections, and they should receive genetic counseling to understand their risk of having a child
with sickle cell disease and obtain prenatal diagnosis if desired. Hemoglobin electrophoresis can also
identify carriers of β-thalassemia, hemoglobin C, or rarer hemoglobinopathies. In patients with micro-
cytic anemia, normal iron studies, and normal hemoglobin electrophoresis results, genetic testing for
α-thalassemia should be performed.
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15. What is the purpose of the rubella antibody titer?
Congenital rubella syndrome is now rare because of widespread vaccination; however, many adults
(10% to 15%) exhibit susceptibility on serologic testing. Because the rubella vaccine is live attenuated
virus given as part of the MMR (measles, mumps, rubella) vaccine, women who are seronegative
should be immunized post partum.
16. Is serologic testing for syphilis still important?
Yes. Women who test positive should receive the fluorescent treponemal antibody (FTA) test; if the FTA
test result is also positive, syphilis is diagnosed. For more information on this topic, see Chapter 55.
17. Why test for hepatitis B?
Women who are chronic carriers of the hepatitis B virus have a high risk of vertical transmission to
their infants during or after delivery. Many of these infants also become chronic carriers, and this in
turn places them at risk for cirrhosis and hepatocellular carcinoma. The Centers for Disease Control
and Prevention (CDC) recommend that all pregnant women be screened for the hepatitis B surface
antigen and that all newborn infants receive vaccination against hepatitis B. Infants of antigen-positive
mothers should be given hepatitis B immune globulin as well as the vaccine within the first 12 hours
of life.
18. Should pregnant women be screened for human immunodeficiency virus (HIV)
infection?
Absolutely. The ACOG and the American Academy of Pediatrics now recommend screening all
prenatal patients. Positive results from an initial enzyme-linked immunoassay (ELISA) test should
be confirmed by Western blot analysis. Diagnosed women should then be assessed for viral load
(by polymerase chain reaction [PCR]) and referred to appropriate subspecialists. At the time of
delivery, women with a viral load of less than 1000 copies/mL are candidates for vaginal delivery.
Women with higher viral loads should be delivered by cesarean section to reduce the risk of vertical
transmission. All patients with a viral load greater than 400 copies/mL should be given intravenous
zidovudine (formerly azidothymidine [AZT]) during labor or before a scheduled cesarean delivery.
After birth, infants born to HIV-positive mothers should also be followed and treated by infectious
disease specialists.
19. Of what benefit are tests for other sexually transmitted diseases?
Testing for gonorrhea and Chlamydia should be done in at-risk patients (i.e., those <25 years old,
unmarried, or with multiple sexual partners), and many authorities recommend routine testing for all
pregnant women. Neonatal chlamydial infection occurs in 60% to 70% of infants passing through an
infected birth canal. Conjunctivitis develops in 25% to 50% of exposed infants, and chronic pneumo-
nia occurs in 10% to 20%. Before mandatory use of ophthalmic antibiotic prophylaxis after delivery,
gonorrheal transmission at birth caused blindness in many newborn infants (gonococcal ophthalmia
neonatorum). Gonococci can also cause chorioamnionitis after preterm premature rupture of mem-
branes (PPROM), resulting in a high rate of prematurity and infant morbidity.
Women who test positive for gonorrhea or Chlamydia infection should be treated and a test of
cure obtained. Repeat testing should also be performed at 36 weeks of gestation. For more informa-
tion on this topic, see Chapter 55.
20. Which laboratory tests are repeated during the prenatal course?
• A complete blood count is generally repeated in the third trimester to identify women with anemia.
It can be repeated more frequently in at-risk women.
• Dipstick urine analysis for protein, glucose, leukocyte esterase, and nitrites is done at each prenatal
visit. The presence of significant proteinuria (1+ or greater) should prompt further testing for pre-
eclampsia, urinary tract infection, or renal disease. The presence of nitrites or leukocyte esterase
should prompt further testing for urinary tract infection. Although glucose testing is performed,
glucosuria has poor specificity and can be present in healthy pregnancy women.
• Antibody screening test is repeated at 28 weeks of gestation in Rh-negative women.
• Sexually transmitted disease testing is frequently repeated in the third trimester for at-risk
women.
21. Should pregnant women be screened for tuberculosis?
The incidence of tuberculosis nationwide has declined since 1992. However, this infection remains
a problem for women born in foreign countries with high infection rates. Screening is therefore
encouraged for women who have immigrated from Asia, Africa, or Latin America or for women who
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have other risk factors. Newborn infants are especially susceptible to tuberculosis, and active disease
should be ruled out in women who screen positive. Treatment is acceptable in pregnancy if indicated;
in the absence of active disease, it can be deferred until after delivery.
22. Why is GBS screening done during pregnancy?
GBS infection is a cause of neonatal sepsis and carries high rates of neonatal mortality and morbid-
ity, especially in premature neonates. Eradicating the organism with an antibiotic (usually penicillin)
at the time of delivery is the best means of preventing early-onset neonatal GBS sepsis. The CDC
currently recommends routine screening of all mothers for GBS at 35 to 37 weeks; for women
with unknown screening results or unknown GBS status, treatment is determined by risk factors
(e.g., <37 weeks of gestation, membrane rupture >18 hours, maternal fever in labor). Intrapartum
prophylaxis should be given to all patients with GBS bacteriuria or a history of a previous infant
with GBS disease.
23. Who should be screened for gestational diabetes (GDM), and how should this be
done?
The ACOG recommends that all pregnant women be screened for GDM, whether by clinical risk factors
(Table 36-2), medical history, or laboratory screening tests. The most commonly used laboratory test is
the 1-hour, 50-g oral glucose challenge test. It is performed at 24 to 28 weeks of gestation. Additional
testing can be done at the initial prenatal visit for patients at high risk for gestational diabetes (e.g.,
history of GDM in a previous pregnancy, morbid obesity, strong family history). The literature does not
clearly support using one cutoff value compared with another; screening thresholds of 130 to 140 mg/dL
have been used, with varying sensitivity and specificity.
Patients with abnormal 1-hour test results should have a 3-hour, 100-g oral glucose challenge
test; the test result is considered positive if the fasting level is higher than 125 mg/dL or if any two of
the following are present:
• >95 mg/dL fasting
• >180 mg/dL at 1 hour
• >155 mg/dL at 2 hours
• >140 mg/dL at 3 hours
24. What is the purpose of nuchal translucency (NT) measurement and serum
biochemical marker screening?
The ACOG recommends that all pregnant women—regardless of age—should be offered aneu-
ploidy screening before 20 weeks of gestation. The NT measurement is offered between 11 and
14 weeks of gestation; abnormally large (>3.5 mm) measurements indicate an increased risk
for aneuploidy and congenital heart defects. Aneuploidy detection is improved when the NT is
combined with biochemical serum markers in the first or second trimester. Various biochemical
screening protocols are available, including the triple screen, the quad or quadruple screen, the first
trimester combined screen, the sequential screen, and the integrated screen. Patients who screen
Table 36-2. Risk Factors for Gestational Diabetes*
HIGH RISK
(ANY REQUIRED)
LOW RISK
(ALL REQUIRED)
Previous macrosomic infant <25 years of age
Previous stillbirth Negative family history
Previous gestational diabetes Normal body habitus
Family history of diabetes Ethnic background with low prevalence
Obesity No earlier poor obstetric outcomes associated
with gestational diabetes
Ethnicity: Hispanic, African American, Native American,
East or Southeast Asian, Pacific Islander
*The presence of any high-risk factor should prompt further screening. For no additional screening to be
considered necessary, all low-risk factors must be present.
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positive should be referred for genetic counseling and offered diagnostic testing with chorionic
villus sampling or amniocentesis, depending on gestational age. For more information on this topic,
see Chapter 39.
25. Should a routine prenatal ultrasound scan be done?
Yes. Ultrasound examination can show many major fetal anomalies. Ninety percent of infants with
congenital abnormalities are born to women who do not have any risk factors, and pregnant women
should have at least one ultrasound examination during pregnancy to assess fetal anatomy. This
examination is generally done at 18 to 20 weeks of gestation. Ultrasound has not been shown to be
harmful to a developing fetus.
26. Should any routine medications be prescribed during pregnancy?
Most authorities recommend supplemental iron because it is often difficult to meet the iron require-
ments of pregnancy by diet alone. Most prenatal vitamins contain 40 to 65 mg of elemental iron.
Adequate intake of folic acid, a key component in neural tube development, should be started before
pregnancy. For more information on this topic, see Chapter 37.
27. Can pregnant women exercise during pregnancy?
Yes. Most women can continue some form of exercise during pregnancy. For these women, aerobic
exercise is recommended for at least 15 minutes three times per week. Women should continue
activities they were familiar with before pregnancy, but avoid contact sports or activities with an
increased risk of falling (e.g., skiing, horseback riding, gymnastics). For more information on this topic,
see Chapter 37.
28. Should pregnant women be screened for intimate partner violence (IPV) or
domestic violence?
Yes. The rate of IPV in pregnancy is estimated to be from 1% to 20%. As a group, victims of domestic
violence are at high risk for poor pregnancy outcome and are likely to commence prenatal care late in
pregnancy. The leading cause of maternal mortality is homicide, and most cases are associated with a
history of IPV. For more information on this topic, see Chapter 20.
29. What advice should be given to pregnant women regarding work outside the
house?
In general, women with low-risk pregnancies can continue working at their regular jobs as long as the
job is not dangerous (physically or environmentally) or overly strenuous. Job requirements often can
be modified to reduce the physical workload, or the patient can be transferred to a role that requires
less strenuous work. Frequent breaks, elevation of legs, and changes in position are all helpful.
By federal law, employers offering medical disability compensation must treat pregnancy-related
disabilities in the same manner as temporary disabilities (illness or injury) suffered by nonpregnant
employees. Such temporary disability can result from pregnancy per se (e.g., musculoskeletal symp-
toms), complications of pregnancy, or hazardous occupational exposure during pregnancy. If employee
disability coverage is not available, the patient may be eligible for state unemployment benefits, or
she must use sick leave or vacation time or take an unpaid leave of absence. The Family and Medical
Leave Act of 1993 provides that any pregnant woman working for a government or a company of
more than 50 employees is allowed up to 12 weeks of nonpaid maternal leave, during which time the
employer must continue her benefits and seniority and retain her job position or equivalent for when
she returns.
30. Which common complications of pregnancy can be prevented or minimized by
good prenatal care?
• Anemia from iron or folic acid deficiency
• Urinary tract infections and pyelonephritis
• Pregnancy-induced hypertension (preeclampsia)
• Preterm delivery
• Intrauterine growth retardation
• Sexually transmitted diseases and their effect on the newborn infant
• Rh isoimmunization
• Fetal macrosomia
• Breech presentation at term
• Hypoxia or fetal death from postterm birth
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