Most birth defects don't rise with age.

Most birth defects don't rise with age

Many women who postpone childbearing until their late 30s wonder whether their age increases the odds of having a child with a birth deect. For certain chromosomal disorders such as Down's syndrome, the unfortunate answer is yes. But a study of birth defects that result from unknown causes -- representing more than three-quarters of all congenital defects -- offers good news for thirty-something women.

Researchers at the University of British Columbia in Vancouver have completed what they call the first rigorous analysis of whether nonchromosomal birth defects increase with maternal age. The team, led by Patricia A. Baird, obtained records for the more than 500,000 live births occurring in British Columbia between 1966 and 1981. These records, they say, provide reliable data on maternal age and defects observed at birth. In order to include congenital defects not diagnosed at birth, the researchers tracked each child for up to seven years. In all, they identified roughly 27,000 children with birth defects of unknown cause.

In analyzing data on women who gave birth between their early teens and late 40s, Baird and her colleagues found no association between birth defect rates and advancing maternal age. Of the 43 types of birth defects studied, only three showed a significant correlation between incidence and maternal age, and two of those -- a heart defect called patent ductus arteriosus and a stomach defect called hypertrophic phyloric stenosis -- actually decreased with increasing maternal age, the researchers report in the March 2 LANCET. The third, a congenital hip dislocation, showed increased incidence until age 30, but then decreased again in women over 30.

The results should be "very reasuring" to pregnant women over 35 who have undergone fetal testing that showed no detectable chromosomal disorders, Baird says. These women, especially if they have no other fetal risk factors such as diabetes or alcoholism, "are not at any greater risk [for birth defects] than if they were in their 20s," she told SCIENCE NEWS.

Robert J. Clayton, a birth defects specialist at the University of Texas Health Science Center at San Antonio, says the study is extremely valuable because the researchers were able to eliminate the "random drifts" in birth defect rates that confound smaller-scale population studies focusing on a single type of defect. The results, says geneticist Maureen E. Bocian of the University of California, Irvine, should extend to the general population, with the exception of isolated, inbred communities.