May 8, 2019

Editor’s Note: This is a review of research[i] published in 2014 in Human Reproduction titled, “Too old to have children? Lessons from natural fertility populations.” It was written by a medical student as part of a two-week online elective taught by FACTS Executive Director, Dr. Marguerite Duane, at Georgetown University College of Medicine. It provides insight into a subject of increasing interest and concern for women who delay childbearing while highlighting the need for more research and education in this area. With Mother’s Day just around the corner, we remind women and couples hoping to conceive that fertility awareness can play a crucial role in achieving pregnancy.

Today, the question of how long one can safely wait before having children is at the forefront of many women and couples’ minds. More than ever before, women are now empowered to postpone pregnancy through a wide variety of birth control methods. Postponing having children has become increasingly common, as women and couples spend time ensuring career success, achieving financial stability, and finding suitable partners before trying to have children.

This is the case for many of my peers and for me, and a topic we discuss frequently. Inherent in these discussions is anxiety about “how long is too long” to wait to have children before we need to worry about age-related difficulties conceiving as well as potential health risks for our future children and for us. Even as someone trained in medicine, I still feel I do not have clear or adequate information on this topic, and was very interested to read the 2014 study published in Human Reproduction addressing this topic.



The study examined multiple large data sets containing records of nearly 60,000 women (58,051 eligible women) and their age at last birth (ALB). Researchers reviewed high-quality data of natural fertility populations using a retrospective cohort design. The relatively recent wide adoption of electronic records made it possible to conduct this study with a much larger data set representing wider geographies than previous research on this topic. The study population included women from a variety of western geographies and from a broad historical time period (the oldest data was from 200 years ago!).

Data analysis showed the median age at last birth was consistently around 40-41 years across all geographies and time periods included in the study. This finding suggests this is a biologically-determined age at which women’s fertility declines. To break this down further, the researchers constructed a biological age at last birth curve which documented a likelihood of “involuntary childlessness” of 12% at age 35, 20% at age 38, 50% at age 41, and nearly 90% at age 45. By age 50, the likelihood of involuntary childlessness approached 100%.

The median age of last birth identified by the study, 40-41 years of age, is notably higher than 35 which, according to the article, is the age around which there is “unsubstantiated pessimism regarding the possibility of natural conception.” It is also noteworthy that this study included only natural fertility populations, meaning the individuals included in the study made no conscious effort to limit, regulate, or control their fertility. Further investigation is needed to better understand the effects of modern birth control methods on fertility.

The biological age at last birth curve created by the researchers can be a useful tool for individuals seeking to plan their families and for health care professionals who need to counsel patients. The study concludes with the following advice to women thinking about having children: “the curve contradicts the occasionally exaggerated pessimism about women who intend (or by circumstances are forced) to have children in their late thirties (Twenge, 2013).[ii] For them the lesson is: you still have a good chance to succeed if you don’t wait any longer. For women in their early forties the lesson is: just try, your chances are still far from hopeless.”


Editor’s Note: Readers interested in further reading on this subject are referred to the extensive list of references included in the research article. The biological ALB curve referenced above can be found here.


[i] Eijkemans MJ, van Poppel F, Habbema DF, Smith KR, Leridon H, te Velde ER. “Too old to have children? Lessons from natural fertility populations.” Hum Reprod. 2014 Jun;29(6):1304-12. PubMed PMID: 24676403.
[ii] Twenge, Jean M. “How Long Can You Wait to Have a Baby?” The Atlantic, July 2013.



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