Tests During Pregnancy

AFP Testing

AFP testing is a simple blood test performed at about 15 weeks of pregnancy. This is a test that identifies those women who are more likely to have a baby with an open neural tube defect. It cannot diagnose problems with your baby or pregnancy.

Spina bifida occurs when the baby's neural tube, or spine, does not close completely during development, leaving the spinal cord exposed. Approximately 1 in 1000 babies has open spina bifida.

Amniocentesis

Amniocentesis is a procedure in which amniotic fluid surrounding the baby inside the womb is obtained for testing. These include tests for chromosomal abnormalities, such as Downs Syndrome, and tests for the presence of open neural tube defects such as spina bifida and anencephaly. In later pregnancy, amniotic fluid obtained by amniocentesis can help your doctor know whether your baby's lungs are mature.

Amniocentesis is performed in our office by giving a local anesthetic and then inserting a sterile needle through the abdominal wall into the womb. Ultrasound imaging is used to help locate a safe and available pocket of fluid. The fluid is withdrawn and sent to a laboratory for testing.

Cystic Fibrosis Screening

What is cystic fibrosis?

Cystic fibrosis is a life-long illness that is usually diagnosed in the first few years of life. The disorder causes problems with breathing and digestion, because of altered mucus production in affected individuals. Cystic fibrosis (CF) does not affect intelligence. The average life expectancy of affected individuals approaches forty years.

How is cystic fibrosis inherited?

Cystic fibrosis is a genetic disorder. All genes come in pairs, one from the mother and one from the father. Some genes do not function properly because there is a mistake in them. Everyone has two copies of each gene.

For CF to occur, a person has to inherit an altered gene from each parent. If a person inherits one copy of a CF gene with a mistake, that person is a "carrier" for CF, and does not have CF. There are no known health problems associated with being a carrier. To have CF, an individual must inherit a defective CF gene from both carrier parents. If both parents are carriers, there is a one in four chance that any one of their children will have CF. There is a one in two chance that any of their children will be carriers, and a one in four likelihood that a child will be neither a carrier nor affected.

How common is cystic fibrosis?

The rate of defective CF genes varies in different groups of people. In Caucasians, one in every 29 individuals is a carrier of a CF mutation, and roughly one in every 3,300 newborns will have cystic fibrosis. In Hispanic populations, the carrier rate is lower, at one in 46, with about one in 8,000 to 9,000 children being affected. In African-Americans, one in 62 are carriers, with a newborn rate of roughly one in 15,000. Among Asian-Americans, one person in 90 is a carrier, and among their newborns, only one in 32,000 will have CF.

How can I find out if I carry the gene for cystic fibrosis?

A DNA test on white cells from a blood sample can tell a patient whether they are likely to be a carrier of a defective CF gene. Because there are so many different mutations in the CF gene that can make it function incorrectly, this DNA test cannot practically check for all of them and, instead, screens for the most common mistakes. Because the likelihood of finding a patient with a defective CF gene among Caucasians is so much higher, and because of clustering of certain defective genes in some populations, the detection rate for the problem is about 97%, while among other groups it can be as low as 57%. This means that among some ethnic groups with very low rates of being CF carriers, the blood test is only likely to detect this a little more than half the time.

What if the test is positive?

If the initial blood testing returns positive for a defective CF gene, the other partner is then tested. If this test returns negative, the likelihood of having an affected child is very low. If the testing should be positive for both the patient and her partner, the likelihood that any child born to them will have cystic fibrosis is one in four. Additional testing during the pregnancy can show whether or not the fetus will have cystic fibrosis.

Should I have the test for cystic fibrosis?

It is suggested by the American College of Obstetrics and Gynecology that screening for CF be offered to those patients with the highest risk for the disease, including Caucasians and Ashkenazic Jews. For others, we provide this written information for their consideration. If they desire further information or counseling, this is also given.

The test is also offered to patients with a family history of cystic fibrosis or whose partners have CF themselves.

The decision to proceed with testing is an individual one, and we will support your decision in either direction. Payment for carrier testing is quite variable at the moment among insurance companies. Because testing is not inexpensive, you should check with your insurance company.

Where can I obtain further information?

We will be happy to discuss cystic fibrosis screening further with you during your visits to our office. Other resources for additional information include:

• Cystic Fibrosis Foundation
• Boomer Esiason Foundation

Gestational Diabetes Testing

Gestational Diabetes Testing is routinely performed on all patients at twenty-eight weeks of pregnancy. The test involves not eating for at least three hours prior to the visit, then drinking a known amount of a glucose-containing "beverage". One hour after consuming this solution, a blood sugar measurement is obtained.

If you pass this initial screen for diabetes, as most do, no further testing is usually necessary. If your screening value is too high, a confirmatory three-hour glucose tolerance test is arranged. . Although most patients subsequently pass this test, it serves to identify those with gestational diabetes who need more intensive follow up.

Group B Strep

Group B Strep is a bacteria that inhabits the genital tract of up to 40% of female patients. Although this is not a "bad" bacteria, it will cause infections in 2 to 3 pregnancies per 1,000. Since such an infection can be devastating for a newborn, we give Group B Strep positive mothers prophylactic antibiotics when they are in labor in order to lessen the infection risk. If you have been identified as being Group B Strep colonized in the past, we do not perform a culture on you. We routinely culture the vagina of all other obstetrical patients at 35-36 weeks.

This culture involves swabbing the lower portion of the vagina with a Q-tip and then sweeping the Q-tip past the opening of the rectum. If your culture is positive now or has ever been positive you will be treated with antibiotics during labor.

In summary, Group B Strep is a normal bacteria inhabiting the lower genital tract of many patients. Although the bacteria rarely causes infection in the newborn, we treat any Group B Strep positive mothers with antibiotics during labor.