Fertility peaks around age 30 for both males and females, Boston University study finds

Lauren Wise
Lauren Wise

A new study co-authored by researchers from the BU Schools of Public Health and Medicine found that declines in fertility occurred slightly later than previous studies have suggested. Most previous studies have been conducted in fertility clinic populations or populations using natural family planning, whereas this study was conducted in a population of Danish women with no known fertility problems. The study found that among females, fertility declines were not marked until after age 35; women aged 35-40 had a 23% lower chance of conceiving in each menstrual cycle than women aged 20-24. Males had a later and smaller decline in fertility than females, with only a 5% reduction among men aged 35-39. Some of the decline in fertility at older ages was offset by volitional factors affecting conception, such as frequency and timing of intercourse. Despite the somewhat more optimistic view of age-related fertility than in prior studies, the study says that “couples will experience a compounded effect of their separate age-related declines….For example, if both partners are the same age…., then their fecundability at age 40 years is nearly half of what it is at age 30 years.” The study, called Snart Gravid, or ‘Soon Pregnant,’ is a collaboration between researchers at BUSPH and the Univeristy of Aarhus in Denmark. Data for the study, based in Denmark, are collected via the internet and include questions on socio-demographic background, reproductive and medical history, as well as follow-up questions on pregnancy status, frequency and timing of intercourse, and other lifestyle factors. More than 3,700 women, aged 18 to 40, were enrolled.

Dr. Kenneth J. Rothman, Professor of Epidemiology, was the lead author on the study. Other authors of the study included: Elizabeth E. Hatch, Lauren A. Wise, and Henrik Toft Sørensen of the BUSPH Epidemiology Department, and Ellen M. Mikkelsen and Anders H. Riis of the Department of Clinical Epidemiology at Aarhus University Hospital in Denmark.

The study was supported by the National Institute of Child Health and Human Development and the Danish Medical Research Council.

Of additional interest: The research team recently launched a new Internet-based fertility study here in the United States, called PRESTO. For more information about the study, please visit the website.