History: A complete medical history should be obtained, including medical conditions; medication use (prescription, over-the-counter, supplements); diet; use of alcohol, tobacco, and illicit drugs; both family and menstrual history (age of menarche, usual menstrual pattern, date of onset of last menses, contraceptive use, history of irregular menses); and history of previous pregnancies. Many women miss a menstrual period before they suspect pregnancy. Early symptoms may include tender, swollen breasts, nausea, vomiting, frequent urination, and fatigue. Physical exam: The exam may reveal enlargement of the uterus on bimanual examination, softening of the uterus and cervix (Hegar’s sign) at 6 weeks, bluish color of the vagina (Chadwick’s sign) at 8 to 10 weeks, and enlargement of the breasts. At 10 to 12 weeks, fetal heart tones can be heard through a special stethoscope. The uterus may be palpable low in the abdomen by 12 weeks. Tests: Pregnancy can be confirmed through laboratory tests or home test kits that check for hCG in serum or urine. Over-the-counter or home pregnancy test kits can detect hCG in urine and become positive 9 to 12 days after conception. hCG can be detected in the serum in 5% of pregnant women 5 days after conception and in over 98% of pregnant women by 11 days after conception. Serum hCG tests have a low false positive rate of 0.01% to 2%. A false positive test is caused by substances in the woman’s body such as antibodies, rheumatoid factor, or proteins that interfere with the test. False negative tests usually occur with urine samples and usually are due to interference from medications, dilute urine samples, or errors in following testing directions.
Other initial testing may be done to screen for conditions that may affect the health of the mother and fetus. Urinalysis screens for urinary tract infections and kidney problems. Complete blood count (CBC) tests for anemia, infection, and other blood problems. Antibody testing looks for syphilis and rubella (German measles) antibodies and blood group and Rh typing identifies blood group antigens. Individuals at risk for diabetes receive a glucose tolerance test. Additional tests may be done to screen for hepatitis B, toxoplasmosis, and HIV. Cervical cultures may be done to rule out infection.
Ultrasound reveals the age of the fetus, presence of multiple fetuses, abnormal physical development of the fetus, and location of the placenta. Ultrasound carries no known risk to the woman or her fetus. Few studies have been able to prove that ultrasound is absolutely necessary, but it has produced two positive results: fewer pregnancies go past their due dates, and women carrying fetuses with anomalies can make decisions about termination earlier in the pregnancy. Ultrasound can be done at any time, but it is most useful during the second trimester between weeks 18 and 20; a second ultrasound can be done at 23 to 28 weeks.
Prenatal diagnosis of congenital malformations and genetic disorders has increased with the development of accurate testing methods. Testing is often recommended for women who: (1) are age 35 or older; (2) have a history of parental consanguinity; (3) have a personal or parental history of a child with a chromosomal abnormality (e.g., Down syndrome, male relatives with Duchenne muscular dystrophy, severe hemophilia); (4) have experienced recurrent miscarriages; (5) has type 1 diabetes mellitus, epilepsy, or myotonic dystrophy; (6) has been exposed to certain medications, environmental hazards, or viral infections (e.g., rubella, cytomegalovirus).
Measurement of alpha-fetoprotein (AFP) levels in maternal blood serum screens for neural tube defects such as absence of all or part of the brain (anencephaly) and protrusion of part of the spinal cord through a gap in the spinal column which usually results in loss of voluntary movement in the lower body (spina bifida). AFP is a protein made by the fetus’s liver. If the fetus's spinal cord has not developed correctly, increased amounts of AFP may leak into the mother's bloodstream. Elevated levels of AFP in the maternal bloodstream can also occur with gestational diabetes, twins, intrauterine growth retardation, increased gestational age, and in pregnancies complicated by bleeding. Low levels of AFP in the mother’s bloodstream may suggest the presence of chromosomal abnormalities such as Down syndrome. Testing is most sensitive at a gestational age of 16 to18 weeks but can be performed anywhere between 15 and 22 weeks of gestation. At 15 to 20 weeks, maternal serum levels of AFP, hCG, and estriol can be measured. Each of these substances is a marker for potential fetal abnormalities. Checking the levels of these markers simultaneously increases screening sensitivity.
Analysis of the amniotic fluid (amniocentesis) that surrounds the developing fetus, is used to detect fetal genetic abnormalities in pregnant women over age 35 or in those whose family history puts them at high risk for certain genetic defects. It is usually performed between weeks 14 and 20 of the pregnancy. Under ultrasound guidance, a long needle is passed through the mother’s lower abdomen into the uterus, and a small amount of fluid is withdrawn. The fetal cells that have been shed into the fluid are analyzed for chromosomal problems (e.g., Down syndrome), and the fluid is analyzed for abnormally high level of AFP. Later in the pregnancy the test can determine the maturity of the fetus's lungs or if there is Rh incompatibility between fetus and mother. The procedure carries an increased risk of miscarriage and maternal Rh sensitization.
Chorionic villus sampling is another form of invasive testing for chromosomal abnormalities and genetic defects. Small pieces of the placenta are removed through a catheter inserted into the uterus under ultrasound guidance. The primary advantage of chorionic villus sampling is that the procedure can be performed at 10 to 12 weeks gestation, whereas amniocentesis is performed at 14 to 20 weeks gestation. The risk of miscarriage with chorionic villus sampling is 2% to 3% higher than for amniocentesis. There is also a small risk of injury to the developing fetus’ limbs.
Percutaneous umbilical cord sampling is used after 16 weeks gestation for rapid chromosome analysis as well as evaluation of fetal metabolism and fetal blood abnormalities. Guided by images on ultrasound, a doctor inserts a needle into the mother’s abdomen and withdraws a sample of the baby’s blood from the umbilical cord. Because this is an invasive procedure, percutaneous umbilical cord sampling carries risks for both mother and fetus.
If the mother is of African origin, a test for sickle cell anemia may be ordered. Jewish mothers of eastern European ancestry (Ashkenazi Jews) and French Canadians should be tested for the Tay-Sachs gene. |