About This Early-Term Prenatal Test
Between 10 and 12 weeks, some women opt to have a prenatal test called CVS (Chorionic Villus Sampling). CVS may be offered if you are over age 35, have a child or a previous pregnancy affected by a birth defect, or if there is other family history of certain birth defects.
CVS is considered to be 98% accurate in the diagnosis of chromosomal defects, such as Down Syndrome.
However, it's important to be aware that CVS carries with it a small risk of miscarriage -- from 0.5% to 1.0%, according to the Centers for Disease Control (CDC). Futher, the American Academy of Family Physicians reports that some studies suggest that in a small number of cases, CVS may cause defects in the baby's fingers or toes if the test is done before nine weeks of gestation (11 weeks of pregnancy, based on menstrual age).
There are two ways to complete this procedure: via the vagina and cervix (transcervical CVS) or through the abdomen (transabdominal CVS). The transcervical method is preferred unless you have a retroverted uterus, in which case, transabdominal is safest. Local anesthesia may be used in some cases.
You should have a full bladder before going for the test. With the help of an ultrasound to visualize the uterus and placenta, a thin needle (through the abdomen) or narrow tube (though the cervix) takes a small tissue sample from the chorionic villi, tiny pieces of placental tissue that attach the pregnancy to the uterine wall. The cells are then tested for chromosomal problems (processed directly or cultured for chromosomal, DNA or biochemical analysis), and results are usually back in about 10 days.
The March of Dimes has noted that that in a national study, 1 in 5 women experience cramping following CVS, and 1 in 3 women have some bleeding or spotting, which usually stops within a few days.