of the presence of an abnormality, just that there might be a problem. Most turn out perfectly fine, but if your partner does get a positive result, she’ll be asked to take additional tests, such as an ultrasound and amniocentesis, which should clear up any doubts you have. Since these screens are really designed to let your partner know whether she needs additional testing, she may not want to bother if she’s planning to have an amnio or an in-depth ultrasound test.
TESTS YOU MAY HAVE TO TAKE
No, you’re not pregnant, but there are still a few times when you may need to give a little blood to make sure all is well with your baby. A variety of genetically transmitted birth defects, for example, affect some ethnic groups more than others. So, based on your family histories, your partner’s doctor may order one or both of you to get additional blood tests. OB Saul Weinreb told me that “every person in the world is estimated to carry thousands of potentially harmful genetic mutations, which means that every couple has an approximately equal chance of having a baby with a random genetic disease they had no idea they carried.” The good news is that science has been able to identify certain diseases that occur more commonly in certain ethnic groups. So rather than think of these groups as somehow genetically worse off than others, think of them as being lucky that there are tests for conditions that may affect them. New tests are being developed every day. Among the most commonly identifiable conditions are:
• Sickle-cell anemia. If you’re African American or if your family came from the Caribbean, Italy, Sardinia, or India, you may want to be tested whether your practitioner suggests it or not. If your partner knows she’s negative, though, ask the doctor whether you should bother.
• Tay-Sachs and Canavan Disease. If either you or your partner is of Ashkenazi (Eastern European) descent, get tested. Tay-Sachs is also found in some non-Jewish French Canadians. Interestingly, once your partner is pregnant, it is more accurate to test you for these conditions than to test her. If your results come back positive, she’ll need to be tested, though.
• Cystic fibrosis. The American College of Obstetricians and Gynecologists now recommends that OBs offer cystic fibrosis testing routinely.
• Thalassemia. Affects mainly families of Asian, Southeast Asian, African, Middle Eastern, Greek, or Italian origins.
You may also have to be tested if your partner has a negative Rh (for rhesus, like the monkey) factor in her blood. If you’re positive (and most of us are), your baby might be positive as well. If this is the case, your partner’s immune system might think the Rh-positive baby is some kind of intruder and try to fight it. This can lead to fetal brain damage or even death. Fortunately, this problem is preventable: your partner will have to get some anti-Rh injections, starting around the 28th week of the pregnancy.
INVASIVE PROCEDURES
AMNIOCENTESIS
This extremely accurate test is usually performed at 15–18 weeks, and can identify nearly every possible chromosomal disorder, including Down syndrome. It can’t, however, detect deformities such as cleft palate. If your baby is at risk of any other genetic conditions, your partner’s doctor can order additional testing (but these tests are not done routinely). Amnio is also sometimes used in the third trimester of pregnancy to help doctors determine whether the fetus’s lungs are mature enough to survive an emergency premature delivery, if they’re worried about that. The test involves inserting a needle through the abdominal wall into the amniotic sac, where about an ounce of fluid is collected and analyzed. Results are usually available in one to three weeks. Unless your partner is considered at high risk (see page 61), or either of you needs to be reassured that your baby is healthy, there’s no real reason to have this test. The chances that a twenty-five-year-old woman will give birth to a baby with a defect that an amnio can detect are about 1 in 500. The chances that the procedure will cause a miscarriage, however, are 1 in 200. For women over thirty-five, though, amnio begins to make statistical sense: the chances she’ll have a baby with chromosomal abnormalities are roughly 1 in 190 and rise steadily as she ages. At forty, they’re about 1 in 65; at forty-five, 1 in 20.
Reasons Your Partner (or You) Might Consider Genetic Testing
• One of you has a family history of birth defects, or you know you’re a carrier for a genetic disorder such as cystic fibrosis, muscular dystrophy, or hemophilia.
• One of you is a member of a high-risk ethnic group, such as African Americans, Native Americans, Jews of Eastern European descent, Greeks, Italians, and others (see “Tests You May Have to Take,” pages 59–60).
• Your partner is thirty-five or older.
• Your partner has had several miscarriages.
• Your partner had a positive Triple (or Quad or Penta) Screen (see page 59).
• One of you might be a carrier of specific genes that have been linked with birth defects.
Other Reasons for Prenatal Testing
Prenatal testing is also available to people who, while not considered at risk, have other reasons for wanting it done. Some of the most common reasons include:
• Peace of mind. Having an amniocentesis or a Chorionic Villi Sampling (CVS) test can remove most doubts about the chromosomal health of your child. For some people, this reassurance can make the pregnancy a much more enjoyable—and less stressful—experience. If the tests do reveal problems, you and your partner will have more time to prepare yourselves for the tough decisions ahead (for more on this, see pages 71–72).
• To find out the sex of the baby (or, in some cases, to determine who the biological father is).
CHORIONIC VILLI SAMPLING (CVS)
Generally this test is performed at 9–12 weeks to detect chromosomal abnormalities and genetically inherited diseases. The test can be done by inserting a needle through the abdominal wall or by threading a catheter through the vagina and cervix into the uterus. Either way, small pieces of the chorion—a membrane with genetic makeup identical to that of the fetus—are snipped off or suctioned into a syringe and analyzed. The risks are about the same as for amnio, and the two tests can identify pretty much the same potential abnormalities. The main advantage to CVS is that it can be done a lot earlier in the pregnancy, giving you and your partner more time to consider the alternatives. That’s why the number of amnios is falling, while CVSs are rising.
Cell-Free Fetal DNA
One of the most exciting developments in prenatal testing is Cell-Free Fetal DNA (also called cfDNA or cffDNA) testing, which has the potential to eliminate the need for the vast majority of invasive diagnostics. Cell-Free Fetal DNA testing, which can be done as early as 10 weeks, analyzes tiny bits of the fetus’s DNA that are running around in the mom-to-be’s blood. According to Diana Bianchi, a pediatric geneticist at Tufts Medical Center, the results are ten times more accurate in predicting Down syndrome, and five times more accurate in predicting several other genetic conditions. The CffDNA test is nearly 100 percent accurate in ruling out problems, meaning that a negative result should relieve your anxieties. But it does produce some false positives, so a positive diagnosis would still need to be confirmed by amnio, CVS, or PUBS. Still, according to Bianchi, “Nine out of 10 women who are currently being referred for further
