Читать книгу You: Having a Baby: The Owner’s Manual to a Happy and Healthy Pregnancy - Michael Roizen F. - Страница 42

No, it’s not an exposé on the drugstore chain; we’re talking about the diagnostic test called chorionic villus sampling (CVS). Here’s how it works: Because the placenta is made up of cells that derive from the same fertilized egg as the fetus, it’s an ideal resource for DNA that can reveal any genetic abnormalities in your developing baby (or for a paternity test). Chorionic villus sampling, performed between the tenth and twelfth weeks of pregnancy, entails removing a tiny sample of cells from the placenta. The specimen is then cultured in a laboratory, and the DNA is examined for genetic content.

Because CVS is an invasive test and carries a very small (less than 1 percent) chance of miscarriage, it’s generally performed when there’s an indication of risk: if you’ve had a prior pregnancy that involved a genetic problem, if there’s a history of genetic disease in either your family or the baby’s father’s, if you had an abnormal first-trimester screen or nuchal translucency test (see page 303), or if you will be thirty-five or older (although some do not follow the age indication) at the time of delivery and therefore at higher risk of having a baby with Down syndrome. While CVS can detect up to two hundred different genetic defects with 98 percent to 99 percent accuracy (including Tay-Sachs disease, cystic fibrosis, and hemophilia), it cannot detect neural tube defects such as spina bifida (more on page 112), which can be picked up by amniocentesis. The advantage of CVS over amniocentesis is that you can have the test done much earlier, as amnio is usually performed between sixteen and twenty weeks.

To prepare for your CVS, drink heavily beforehand (water, please), because you’ll need a full bladder. Your doctor will first perform an ultrasound to assess the baby’s position and the orientation of your uterus to determine whether she’ll do the CVS vaginally, threading a catheter through your cervix, or abdominally, via needle biopsy. In either case, you might experience slight cramping during and after the procedure, as well as light spotting if you had it done vaginally. You should plan to have someone drive you home and you’ll need to take it easy for the rest of the day. By the following day, you should feel fine; if you experience increased bleeding, vaginal discharge, or fever, call your doctor immediately. Some docs will have you come in a few days after the procedure for a follow-up ultrasound just to make sure everything is okay. Results will be ready in one to two weeks.