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Commercial kits are available for the diagnosis of pregnancy, all of which depend on detection of human chorionic gonadotropin (hCG) by an antibody. Some tests can detect hCG at levels as low as 25 mlU/mL or as early as 1 week after implantation.
Home tests have relatively high positive predictive values. Some of these tests, however, may have high rates of false-negative results.
History and Physical Examination
It is important to identify patients at significant risk of having an abnormal fetus or child. This identification may be accomplished by compiling a complete history. The patient should be asked about past pregnancies associated with malformations; family history (eg, mental retardation, Down syndrome, NTDs, or other genetic diseases); ethnicity (eg, Eastern European Jewish origin, Mediterranean origin, African origin); and any testing that has been performed (eg, for Tay-Sachs disease, sickle cell disease, or cystic fibrosis).
The pelvic examination to ascertain uterine size and gestational age and estimate the expected date of delivery. If there is a discrepancy between uterine size and the last menstrual period.
Nutrition and Weight Gain
All pregnant women should be encouraged to eat a well-balanced diet. Supplemental folic acid is recommended in the preconceptional and early prenatal period to prevent NTDs.
Recommendations are based on the prepregnancy body mass index, defined as weight (in kilograms) divided by height (in meters) squared. Underweight women (body mass index <19.8) should have a weight gain
Work During Pregnancy
A woman who has an uncomplicated pregnancy and a normal fetus and who is employed where there are no greater potential hazards than those encountered in routine daily life in the community may continue to work without interruption until the onset of labor. In addition, she may resume working 4-6 weeks after an
Exercise During Pregnancy
In the absence of obstetric or medical complications, a pregnant woman may engage in a moderate level of physical activity. Exercise will help a pregnant woman maintain cardiorespiratory and muscular fitness throughout pregnancy. Contraindications to exercise during pregnancy include
Follow-Up Visits
Examination at each subsequent visit should generally consist of measurement of the uterine fundus, determination of fetal heart tones, measurement of blood pressure, and determination of fetal presentation. The urine should be screened for glucose and protein at each visit.
The interval for subsequent prenatal visits should be based on patient needs; in general, women with uncomplicated pregnancies should be seen every 4-5 weeks until 28 weeks of gestation, then every 2 weeks until 36 weeks, and then at least weekly until delivery. More frequent visits may be of benefit in monitoring women with diabetes, hypertension, threatened preterm birth, postterm pregnancies, and other complications.
MULTIFACTORIAL ABNORMALITIES
Multifactorial disorders are caused by a combination of factors, some genetic and some nongenetic (ie, environmental). Multifactorial disorders recur in families, but are not transmitted in any distinctive pattern. Many single-organ system congenital anatomic abnormalities are multifactorial, with an incidence in the general population of 1 per 1,000. Examples of multifactorial traits include the following:
• Cleft lip, with or without cleft palate
• Congenital cardiac defects
• Diaphragmatic hernia
• Hydrocephalus
• Müllerian fusion defects
• NTDs
• Omphalocele
Techniques
MATERNAL SERUM TESTING
Genetic amniocentesis to identify fetal aneuploidy in women age 35 years and older (as of the estimated delivery date) has been available for 25 years. Age 35 roughly corresponds to the time when the incidence of maternal age-related trisomies starts to
AMNIOCENTESIS
Amniocentesis for prenatal diagnostic testing is usually offered between 15 and 20 weeks of gestation. Under ultrasound guidance, a 20-22-gauge spinal needle is passed into the amniotic fluid. The initial aspirate
CHORIONIC VILLUS SAMPLING
Indications for CVS are essentially the same as those for amniocentesis, except for analyses that require amniotic fluid rather than amniotic fluid cells. The primary advantage of CVS is that results are available much earlier in pregnancy, which decreases parental anxiety when results are normal and, when they are abnormal, allows earlier and safer methods of pregnancy termination. Earlier diagnosis may also be required
PERCUTANEOUS UMBILICAL CORD BLOOD SAMPLING
Percutaneous umbilical cord blood sampling is also known as cordocentesis. During cordocentesis, the umbilical vein is punctured and blood is withdrawn under ultrasound guidance. Cordocentesis has also been
FETOSCOPIC TISSUE SAMPLING
Some conditions not diagnosable by conventional means of invasive prenatal diagnostic testing may be detected by fetal tissue sampling. Fetal tissue sampling can be performed either by fetoscopy, with its rather