The First Trimester

ROUTINE TESTS

* Initial Blood Tests: A blood sample will be screened for a number of conditions. A complete blood count (CBC) will determine whether you have enough hemoglobin in your red blood cells; too little can be a sign of anemia, which can make you tired and weak. Another test will determine your blood type and whether your Rh factor, a protein found on red blood cells, is positive or negative. In addition, you'll be screened for hepatitis B, which can put your baby at risk of future liver disease if it's not treated. Finally, you'll be screened for antibodies to rubella (German measles) and chicken pox; if you aren't immune, exposure during pregnancy can cause birth defects.

When performed: At your first prenatal visit (usually six to eight weeks into your pregnancy)

Results and follow-up: If you're low on iron, your doctor will likely have you take a daily supplement along with your prenatal vitamin. If you're part of the 10 to 15 percent of the population who lack the Rh protein (you're Rh-negative) and your baby is Rh-positive, injections of Rh immune globulin (Rhlg) can prevent your body from producing antibodies that may attack the fetus. If you're infected with hepatitis B, doctors will give your newborn medication and the hepatitis B vaccine soon after birth. It's 95 percent effective in preventing the disease in infants. Finally, many women in this country are immune to rubella and chicken pox from childhood immunizations, but if you don't think you've been vaccinated, speak with your doctor.

* Sexually Transmitted Disease (STD) Tests: A blood test can check for HIV, the virus that causes AIDS, which can cross the placenta before or during delivery and infect the fetus. The cervix is also swabbed and tested for gonorrhea and chlamydia (untreated, both can cause preterm delivery or eye infections in the baby), while a blood test screens for syphilis (unchecked, it can cause miscarriage or stillbirth). If you have symptoms of herpes, a culture can confirm the condition.

When performed: At your first prenatal visit

Results and follow-up: If you're a carrier of HIV, you'll be given medication during pregnancy and delivery that decreases the risk of mother-infant transmission from 25 percent to about 7. If you have gonorrhea, chlamydia, or syphilis, you'll be treated with antibiotics that are safe for your fetus. If you have herpes, an antiviral medication can control breakouts. If a herpes infection is active at the time of delivery, your doctor may recommend a c-section.

* Pap Smear: Cells are swabbed from your cervix to detect cervical cancer.

When performed: At your first prenatal visit

Results and follow-up: If the test reveals precancerous or cancerous growth, which affects less than 1 percent of women, treatment will begin during or after pregnancy, depending on how advanced the cancer is.

* Blood Pressure: The standard armband test reveals any sudden changes.

When performed: At each prenatal visit

Results and follow-up: A spike, along with protein in your urine, may indicate preeclampsia (high blood pressure during pregnancy). The condition, which affects between 5 and 8 percent of pregnant women, can keep your baby from gaining weight properly, cause the placenta to separate from the wall of the uterus, and put you at risk for a stroke, liver dysfunction, and other problems. Mild cases can be treated with bed rest; severe ones may require antihypertensive drugs or an early delivery.

* Urine Tests: These check for protein (a possible sign of preeclampsia; see above), sugar (too much may signal gestational diabetes), and, in some cases, for blood and bacteria (which could indicate a urinary-tract infection).

When performed: At each prenatal visit

Results and follow-up: Gestational diabetes, which can make your baby grow too quickly, rarely develops until the second or third trimester. Milder cases may be controlled with diet, and in more severe cases, insulin. A urinary-tract infection can be cured with baby-safe antibiotics (untreated, it can lead to a kidney infection and preterm labor).

* Ultrasound: A handheld instrument is moved across your belly or placed inside your vagina, and the sound waves it emits produce images of your fetus. An early ultrasound, at around nine weeks, is used to determine the age, rate of growth, position, and heart rate of your baby, and whether you're carrying multiples. It's standard to have a second one at 18 to 20 weeks, when you can learn the baby's gender. An ultrasound also looks at the placement of the placenta and the amount of amniotic fluid in the uterus. It can reveal some birth defects, such as a heart defect, cleft palate, or spina bifida (an opening in the spine). Most doctors use two-dimensional technology, though 3-D may be available in some larger cities.

When performed: Most women will be given two, the first at 9 weeks, and then at 18 to 20 weeks.

Results and follow-up: Follow-up depends on the reason for the ultrasound. If your ob was trying to determine the fetus's age, your due date may be adjusted. If she suspects a condition such as spina bifida, you have the option of more tests (see "Additional Tests," below) to verify the diagnosis.

ADDITIONAL TESTS

* Cystic Fibrosis (CF): This blood or saliva test determines whether one or both parents are carriers of CF, a genetic disorder that causes lifelong problems with digestion and breathing. If both parents are carriers, there is a one in four chance that their baby will have CF.

When performed: During the first or second trimester, ideally before 20 weeks

Results and follow-up: CVS (see below) or amniocentesis can confirm a diagnosis.

* Chorionic Villus Sampling (CVS): This procedure tests for such genetic disorders as Down syndrome, sickle-cell anemia, and cystic fibrosis. A small cluster of cells is withdrawn from the chorionic villi, which are tiny parts of the placenta, either through a vaginal catheter or through a needle inserted into the abdomen. CVS cannot detect an open neural tube defect (when the spinal cord is exposed). It's an option for women over age 35 (the risk of chromosomal abnormalities increases with age) or those with a family history of chromosome disorders. There are risks involved: Up to 1 in 100 women will have a miscarriage as a result of the procedure.

When performed: At 10 to 13 weeks

Results and follow-up: The results, which are more than 99 percent accurate, are generally available within ten days. A faster test, known as "FISH" (fluorescent in situ hybridization), can quickly check for five major chromosomal abnormalities, one of which points to Down syndrome; this test gives results in a day or two. The main advantage of CVS is that it can be done early in the pregnancy.

* Nuchal Translucency Screening: This relatively new test, which is a combination of two tests, screens for Down syndrome earlier than standard second-trimester testing, and may be helpful in detecting other disorders in the first trimester as well. A specialized ultrasound measures the fluid accumulated in the nape of the fetus's neck (the nuchal measurement); too much can be a sign of Down syndrome. A blood test measures hormone levels associated with increased Down syndrome risk. The test doesn't incur the miscarriage risks of CVS or amniocentesis, but it isn't widely available yet, so check with your doctor about finding a hospital that offers it.

When performed: At 11 to 13 weeks

Results and follow-up: Researchers believe that the accuracy of nuchal translucency screening may be as high as 90 percent. If your results show a risk of an abnormality, you'll be offered CVS or amniocentesis to confirm the diagnosis.

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