Testing During Pregnancy

Learn about the tests you will take during your pregnancy.

Prenatal Labs

The routine prenatal lab panel consists of a routine blood count, a test for rubella antibodies, the pap smear, genital cultures, a test for syphilis, hepatitis B, HIV, blood type and antibody screen. Other testing if necessary might include a sickle cell screen. The American College of Obstetrics and Gynecology and The American Academy of Pediatrics recommends routine HIV testing in pregnancy.

Cystic Fibrosis

Cystic fibrosis is one of the most common inherited diseases in American Caucasians. This disease causes respiratory problems, digestive problems, and infertility. Severity of illness can vary. People with Cystic fibrosis can now live into their 30’s due to advances in the treatment. Cystic fibrosis is an inherited chromosomal disorder. Its inheritance is recessive. As a result, both parents must be carriers to have an affected child. Carriers of cystic fibrosis are asymptomatic. If both parents are carriers of cystic-fibrosis, there is a 25% chance of having an affected child. Approximately 1in 25 Caucasian people will be a carrier of a cystic fibrosis gene. The incidence of carrier status varies based on ethnicity. For example, only 1 in 46 Hispanics and only 1 in 65 African Americans will be carriers of a cystic fibrosis gene. There are many mutations in the cystic fibrosis gene. We are currently able to test for the 32 most common mutations of the cystic fibrosis gene. So, if you carry a gene mutation which isn’t included in this panel, carrier states may be missed. If you do test positive as a carrier of the gene, the next step is to test the baby’s father. If the baby’s father tests negative, the chance of having an affected child is less than 1%.

AFP Tetra

This is a test that is offered between 15 and 21 weeks gestation. It is a screening test for spina bifida and chrosomal abnormalities such as Down’s syndrome. Approximately 1 in 1000 babies has open spina bifida. This test can help to identify 80% of cases of spina bifida. Down’s syndrome occurs in about 1 in 800 births. It is characterized by an extra chromosome 21. Babies with Down’s have some degree of mental retardation, infertility, and physical abnormalities such as heart defects. This test can detect 75 – 80% of pregnancies affected by Down’s syndrome.  Trisomy 18 occurs in 1 out of 8000 births. This disorder is characterized by an extra chromosome 18. Babies with trisomy 18 are typically severely mentally retarded and have severe birth defects. Few live beyond the age of 1 year. This test can detect more than 60% of pregnancies affected by trisomy 18. Being that this is a screening test, it can only tell us if you might be at high risk for one of these conditions. Alone it cannot make the diagnosis. If you do have a positive result, further testing may have to be done. A negative test greatly reduces the likelihood that your baby has one of these problems. It, unfortunately, cannot eliminate the possibility of having a child affected by one of these conditions. If you do have a positive result, you will be offered the following options for further confirmatory testing:

  1. Ultrasound – Ultrasound looks for certain physical features that may be characteristic of any of these conditions. Unfortunately, ultrasound has its limitations. In the hands of a specially trained doctor, 80 – 90% of abnormalities can be detected. None of these conditions can be completely excluded by ultrasound alone.
  2. Amniocentesis – Amniocentesis is the gold standard in the diagnosis of these conditions. During this procedure, a thin needle is inserted into the uterus through your belly. A small amount of fluid is removed and analyzed. 99% of chromosomal abnormalities and 98% of spina bifida can be diagnosed with this test.

Ultrasound

We typically offer an ultrasound for all patients between 18 and 22 weeks. This gives us the opportunity to look for any abnormalities and allows you to get good look at your new baby.

Glucose Challenge Test

The likelihood of developing diabetes increases during pregnancy. This is because of the hormones produced by the placenta. The good thing is that diabetes in pregnancy is short lived and almost always resolves after the delivery. The screening test is called the one hour glucose challenge test. It is usually done between 24 and 28 weeks. Upon arrival for that visit, you are given a drink called glucola (has 50g of sugar). We check your blood sugar one hour later. A passing value is less than 140. Being that this is a screening test, it does have false positives. The confirmatory test is the three hour glucose challenge test. This is only done for people who have an abnormal one hour value.

Group B Strep

This is a test done between 35 and 36 weeks. This culture is looking for bacteria called beta strep. It is normal bacteria. Approximately 10- 30% of people are carriers of beta strep. Carrier status can vary, so even if you were negative with a previous pregnancy, you could test positive for this current pregnancy. Once you have tested positive, we always consider you a carrier of beta strep