Re-evaluating the medical risks of late childbearing.

A critical review of the scientific literature linking advanced maternal age to eight adverse pregnancy outcomes commonly believed to increase with advancing age revealed little support for the pessimistic medical view that late childbearing is necessarily riskier. Most studies (61% of the 104 studies reviewed) were seriously flawed methodologically, primarily by confounding age with other factors; many reached conclusions without statistical verification (29% of the studies reviewed). Results concerning the advantages or disadvantages of late childbearing were inconsistent as well. Evidence from the sound research studies strongly suggests that many of the adverse outcomes found by some researchers to increase at an older maternal age may be reflecting the particular circumstances surrounding late childbearing (altered medical management, pre-existing diseases, subfertility, unplanned pregnancy, high parity birth) rather than a biological condition of aging. Further research must move away from looking at maternal age as an isolated variable because of the temptation to impute causality to the factor when other associated factors are not controlled. A better understanding of the reproductive aging process is urgently needed.