Despite concerns raised from some earlier research, a new study suggests that a prenatal test done to screen for genetic abnormalities does not raise a woman’s risk of developing pregnancy-related high blood pressure.
The test, known as chorionic villus sampling (CVS), is an invasive procedure done to detect Down syndrome and other genetic disorders in some women considered to be at elevated risk - such as those age 35 and older, and women with a family history of a specific genetic disorder.
CVS involves taking a tiny tissue sample from the placenta, and is typically performed between the 10th and 12th week of pregnancy. Doctors consider it an advantage to perform such tests earlier, instead of performing a test such as amniocentesis later in the pregnancy for the same purpose.
Some past studies have found that women who underwent CVS were more likely than other pregnant women to eventually develop pregnancy-related high blood pressure or preeclampsia - a syndrome marked by a sudden increase in blood pressure after the 20th week of pregnancy and a buildup of protein in the urine due to stress on the kidneys.
Preeclampsia can develop into a life-threatening condition called eclampsia, which can cause seizures or coma. It can also slow the growth of the fetus and increase the risks of certain complications, such as preterm birth.
However, a number of studies have failed to find a connection between CVS and pregnancy-related blood pressure problems. One of the larger ones, which included 9,000 pregnant women, found that those who underwent CVS went on to have a lower rate of preeclampsia than women who did not have the prenatal test.
In this latest study, published in the journal Obstetrics & Gynecology, UK researchers followed more than 31,000 pregnant women, of whom 2,278 underwent CVS.
Of the entire group, 3 percent developed pregnancy-related high blood pressure and 2 percent developed preeclampsia. There was no difference in the rates of either condition between women who underwent CVS and those who did not, according to Dr. Kypros Nicolaides and colleagues at King’s College Hospital in London.
According to the researchers, earlier studies suggesting a connection between CVS and blood pressure problems suffered from a number of limitations - including small study populations and an inability to account for other factors that could explain the link.
In one study, for example, women undergoing CVS tended to be heavier than those who did not have the test - and women who are overweight before pregnancy are more likely than normal-weight women to develop preeclampsia. However, the researchers on that study did not account for weight when they calculated the risk of preeclampsia associated with CVS, according to Nicolaides’ team.
In their study, the researchers accounted for factors like weight, smoking and women’s family history of preeclampsia.
It’s thought that abnormalities in the placenta underlie the development of preeclampsia, and researchers have speculated that CVS might contribute to the syndrome by disrupting the placenta. However, the researchers found no evidence of that.
CVS does have certain risks, including a small chance of miscarriage; recent studies suggest the risk is about one in 200. There is also a small risk of infection of the uterus.
The current study was funded by the Fetal Medicine Foundation, a UK charity.
SOURCE: Obstetrics & Gynecology, August 2010.