Women over the age of 35 are more prone to having children with chromosomal abnormalities such as Down syndrome but, according to the findings of a study presented in February, they are less likely to have a child with anatomical abnormalities than younger women. The study revealed a decreased risk of anatomical defects by as much as 40% when the mother is older.

Dr. Katherine R. Goetzinger, an assistant professor of maternal-fetal medicine at the School of Medicine at Washington University in St. Louis (WUSTL), Missouri, led the retrospective study of medical and ultrasound records of 76,156 expectant mothers. Each woman was in the second trimester of pregnancy with no evidence of chromosomal abnormalities.

After undergoing the standard second-trimester ultrasound scan as part of the routine maternity care she was receiving from the WUSTL hospital, 1,804 of the women exhibited evidence of major fetal anomaly. Fetal anomalies were categorized according to body system affected: bones, central nervous system, heart, intestinal tract, and kidney.

The women of advanced maternal age (35 or older) were found to be at 40% less risk of fetal defects than those younger than 35. The rate of heart defects was about the same for women of both age groups but the rate of abdominal wall, brain, and kidney defects were lower in the group of older women.

Goetzinger presented the findings of her study at the 2014 annual meeting — The Pregnancy Meeting™ — of the Society for Maternal-Fetal Medicine in New Orleans, Louisiana. She suggests her findings "may provide some reassurance for these (older) women regarding the likelihood of having an anatomically normal child."

The risk of many pregnancy complications are increased after the age of 35 but a growing number of women in recent years have chosen to delay motherhood well into their thirties. Goetzinger hypothesizes the reduced risk of fetal anatomical defects in older women could be an example of the "survival of the fittest" effect. If so, there's the possibility that the maternal body allows only anatomically healthy fetuses to survive as the chance for reproduction declines with age.

The Society for Maternal-Fetal Medicine, established in 1977, is a professional association of gynecologists and obstetricians who specialize in maternal-fetal medicine. There are approximately 2,000 active society members. In addition to offering opportunities for continuing education to its members, the society advocates for improved public policy and funding that allow for expanded research and other opportunities within the maternal-fetal medical specialty.

Source: "Study Suggests Women 35 and Older are at Decreased Risk of Having Anatomically Abnormal Child."smfm newsroom. SMFM Newsroom. Jan 28, 2014. Web. Apr 9, 2014.