Women in their 40s who spontaneously conceive may be changing the future of fertility, according to a new British study, by making it genetically easier for future generations of "late age" women to become pregnant. Published in the August 2010 issue of the American Naturalist, the study takes the position that when a woman is able to conceive spontaneously past the age of 40, she passes on certain genetic characteristics to her offspring that may, in turn, make it easier for her daughters and grand-daughters to also achieve late-age pregnancies. With more women than ever waiting until their 40s to start having babies, researchers speculate that one day "peak fertility" may extend long past a woman's 30s.
To reach these conclusions, researchers looked at the marriage and birth patterns of Finnish women in the 18th and 19th centuries. Women in this time period tended to reproduce early because they often had no opportunities to do so at an older age (due to marriage patterns and life expectancies). Researchers speculate that early childbearing was genetically reinforced by traits passed on by these women.
"[But] now family-building appears to be increasingly postponed to older ages, when relatively few women in our evolutionary past would have had the opportunity to reproduce. As a result, this could lead to future evolutionary improvements in old-age female fertility," explains study author Duncan Gillespie, from the Department of Animal and Plant Sciences at the University of Sheffield.
Considering waiting until later in life to have a baby? Becoming pregnant in your 40s does carry with the reward of being a wiser—and often more financially secure—mother. But late age pregnancies also carry risk. Other studies have found that women in their 40s are more likely to encounter such health problems as gestational diabetes and gestational hypertension (high blood pressure). For babies, late age pregnancy carries with it an increased risk for Down syndrome.