Fertility Rates, Delayed Marriage, and Infertility

American women—and women around the world—are having fewer babies than they did a generation or two ago. No one who has looked at the data questions that.

Why this is happening—and what the consequences are likely to be—is in greater dispute. Social, biological, and other factors may all play a role and even interact with each other. 

In the social realm, some people celebrate the change as reflecting the empowerment of women. Broader educational and career opportunities, it is argued, have given women more choices and allowed many to postpone motherhood—or forgo it altogether—in pursuit of other life goals. Jill Filipovic, in a guest column for the New York Times in June, praised the end of “compulsory childbearing” and celebrated the fact that “fewer women use motherhood as a conduit to respect and adulthood.”

However, changes in the role of women would not have had such a dramatic effect on birth rates without increases in the availability of contraception and abortion. Another social factor in declining birth rates is a delay in the age at which people first marry. That’s not to say that people always wait for marriage before having babies; on the contrary, the percentage of all births that occur outside of wedlock has dramatically grown (to a total of about 40% of U.S. births). Nevertheless, marriage and childbearing have not been completely decoupled from one another; for example, as the median age of first marriage for women rose in the last decades of the twentieth century (from 20.8 in 1970 to 25.1 in 2000), so did the median age for first childbirth (from 21.4 to 24.9), and these rates have continued to rise since. IFS research fellow Lyman Stone reported in the New York Times in 2018 that among couples who are already married, total fertility rates “have not changed very much over the last 15 years.” But later marriage means fewer married couples at any given time—and that also means fewer babies.

All of this may suggest that declining birth rates are entirely a matter of choice—specifically, of young women choosing career over marriage or motherhood. But that is not necessarily the case. As Stone pointed out in the Times—and explained at greater length on the IFS Blog—survey data have shown that on average, women have fewer children than they say they would like to have. At least to some extent, women have aspirations in favor of childbearing that are unfulfilled. Why?

Again, different answers have been offered. In The Guardian, Moira Donegan wrote in February  that “women are not given enough material support by the state to be able to raise children while still leading prosperous, economically productive lives.” Donegan followed with a litany of complaints regarding the pay gap, pregnancy discrimination, high maternal mortality, the cost of childcare, unpaid child support, the lack of paid maternity leave, and not enough help with housework.

While both expanded opportunities and economic pressures may play a role in reducing the number of births, something more fundamental is also at work—human biology. Demographers use the term “fertility rates” to describe broad population trends. But problems of medical infertility experienced by individuals and couples, like those I (Dr. McIlhaney) saw as patients, should also be considered when examining larger trends in fertility.

I (Dr. McIlhaney) wrote in a 1998 book, “Gonorrhea and chlamydia are spreading like wildfire among young people in the United States. They are the most rapidly increasing cause of infertility in the United States.” I also noted, “Of women who are infertile, one-third have that problem because of damage to their fallopian tubes from one of these two sexually transmitted diseases.” (Damage to the fallopian tubes may prevent sperm from reaching and fertilizing the egg, or it may prevent a fertilized egg from traveling to the uterus and being implanted there.) Back then, statistics clearly showed that if the woman was experiencing infertility, such damage, caused by STDs, was the most likely reason. 

The CDC confirms that the risk of STD-caused fallopian tube damage remains today—but now, it is only the second most common cause for a woman’s fertility problems. Problems of ovulation have taken over the top spot among reasons women struggle to become pregnant. Such problems can be caused by a fairly common disease called Polycystic Ovarian Disease (or Polycystic Ovary Syndrome).  

However, the social trends already noted also have biological implications. Today the median age of first marriage for women is over 28 years of age. The “median” age of first marriage means that half of all women marry for the first time when even older—with many not attempting pregnancy until well after age 30.  Though we were concerned 20 years ago about delayed attempts at conception, those delays generally were not as long as they are today.  

Delays in marriage until later in life do not simply reduce the number of years available for (marital) childbearing. They may make it more difficult to conceive in the first place.

Studies show that fertility begins dropping from age 30 on. More significant decline sets in later in the 30s. Many women’s ovarian responsiveness moves into the zone of what is now called POI (primary ovarian insufficiency), or “premature ovarian failure.”  As POI develops, women have less chance of becoming pregnant without new reproductive technologies (which may be expensive, if they are even available for her). If her ovaries have become even more unresponsive, she will often not have an ovum (egg) that is fertile, or at times, she may have no ovum at all—and therefore, no chance of becoming pregnant without assistance.

So, STD-damaged fallopian tubes are no longer the number one cause of female infertility today. Among women, the number one issue preventing pregnancy is ovulation related. These problems of ovulation are overwhelmingly due to the delayed age at which women are attempting to become pregnant. 

Social trends since the end of World War II have dramatically changed America, expanding the choices available to many people, especially women. Feminism has allowed women to have broader choices in life, without being limited to early marriage and motherhood. Contraception and abortion have made it easier avoid unwanted pregnancy or childbearing. 

But there have been unintended consequences as well. An increase in the number of lifetime sexual partners led to an epidemic of sexually transmitted diseases for men and women. And a delay in marriage has delayed childbearing even for those who aspire to it. Both of these factors have contributed to biological problems of infertility that, for many women, have made the choice to have children more difficult to fulfill. 

Joe S. McIlhaney, Jr., M.D. is a retired ObGyn and the founder of Medical Institute for Sexual Health. Peter Sprigg is Research and Advocacy Director at Medical Institute for Sexual Health.