Pregnancy (Cont.)

2nd Trimester Tests and Procedures

During the second trimester, you should continue to see your doctor for prenatal care. Most pregnant women have monthly office visits with their doctor or midwife until the end of this trimester.

During the second trimester your doctor can use an ultrasound to see if your baby is developing in a healthy way and to find out your baby's sex. You will also be offered screening tests to look for genetic birth defects.

Birth defects result from problems with a baby's genes, inherited factors that are passed down from the mother and the father at conception. Genetic birth defects sometimes occur in people with no family history of that disorder. Women over the age of 35 have the greatest chances of having a baby with birth defects.

Some of the diagnostic and screening tests your doctor might suggest in the second trimester include:

Amniocentesis

This test is performed in pregnancies of at least 16 weeks. It involves your doctor inserting a thin needle through your abdomen, into your uterus, and into the amniotic sac to take out a small amount of amniotic fluid for testing. The cells from the fluid are grown in a lab to look for problems with chromosomes. The fluid also can be tested for AFP. About 1 in 200 women have a miscarriage as a result of this test.

Chorionic Villus Sampling (CVS)

This test is performed between 10 and 12 weeks of pregnancy. The doctor inserts a needle through your abdomen or inserts a catheter through your cervix in order to reach the placenta. Your doctor then takes a sample of cells from the placenta. These cells are used in a lab to look for problems with chromosomes. This test cannot find out whether your baby has open neural tube defects. About 1 in 200 women have a miscarriage as a result of this test.

Maternal Serum Screening Test

This blood test can be called by many different names including multiple marker screening test, triple test, quad screen, and others. This test is usually given between 15 and 20 weeks of pregnancy. It checks for birth defects such as Down syndrome, trisomy 18, or open neural tube defects. Doctors take a sample of your blood. They check the blood for 3 chemicals: alpha-fetoprotein (AFP) (made by the liver of the fetus), and two pregnancy hormones: estriol and human chorionic gonadotropin (hCG). Sometimes, doctors test for a fourth substance in the blood called inhibin-A. Testing for inhibin-A may improve the ability to detect fetuses with a high risk of Down syndrome.

Higher levels of AFP are linked with open neural tube defects. In women age 35 and over, this test finds about 80% of fetuses with Down syndrome, trisomy 18, or an open neural tube defect. In this age group, there is a false positive rate (having a positive result without actually having a fetus with one of these health problems) of 22%. In women under age 35, this test finds about 65% of fetuses with Down syndrome, and there is a false positive rate of about 5%.

Targeted Ultrasound

The best time to get a targeted ultrasound is between 18 and 20 weeks of pregnancy. Most major problems with the way your baby is formed can be seen at this time. Some physical defects such as clubbed feet and heart defects may not be seen.

Your doctor can also use ultrasound to see if your baby has any neural tube defects, such as spina bifida. In most cases, if you want to find out the sex of your baby, you can ask your doctor during this test. This is not the most accurate test for Down syndrome. Only 1 in 3 babies with Down syndrome have an abnormal second trimester ultrasound.

Next: The 3rd Trimester Stage of Pregnancy »