The Myth of the Biological Clock

Parsing the literature on fertility and age.

Posted Jun 14, 2019

Women in many times and places have felt pressure to bear children.   But the idea of the “biological clock” is a particularly malevolent invention aimed to pressure women to have a child.  In her article titled “The Foul Reign of the Biological Clock,” Moira Weigel instructs us that the so-called women’s “biological clock” is a metaphor not an actual biological thing, and that it was invented in the late 1970’s by Richard Cohen in his article, “The Clock is Ticking for the Career Woman."   Within months the “clock” was stalking career women everywhere.  One psychiatrist jokingly diagnosed women who have careers but not children with the “withering womb syndrome.”

We are used to thinking about metaphors like “the biological clock” as if they were not metaphors at all, but simply neutral descriptions of facts about the human body. As a metaphor the biological clock has as much to do with culture as with nature. And its cultural role was to counteract the effects of women’s liberation.  Look at what was happening in the 70’s:       

  • The feminist movement happened.
  • Oral contraceptives and intrauterine devices were developed.
  • The birth rate dropped precipitously.
  • Legalization of abortion occurred.
  • Women were delaying marriage to pursue education and careers.

The existence of a “biological clock” is seen as proof that women should not venture too far from their traditional roles.  Women could dress up in trouser suits but, in the end, their bodies would yearn for children.

The Story

The story of the biological clock is the story about science and sexism—about how assumptions about gender can shape scientific research, and how scientific discoveries can be used to serve sexist goals. Let’s a look at how this metaphor came to shape how we think about women:     

  • Conversations about the “biological clock” pushed women toward motherhood.
  • The metaphor suggested that women who competed with men professionally and were also mothers would do so at a disadvantage.
  • Being female has its limitations, its weaknesses, dictated by female fertility.
  • Reproduction becomes an exclusively female concern.

Unfortunately, the idea of the “biological clock” has not abated.  Here is a recent article about a women worrying about hers—“My Biological Clock is Ticking—But Having Children Seems an Unaffordable Luxury.”[2] 

Dr. Jean Twenge is a psychology professor at San Diego State University who wrote a great article titled “How Long Can You Wait to Have a Baby?” in which she talks about being 30 and in a new marriage in 2002.[3]  She and her husband wanted to have children.  The popular literature at the time included a Time article, which began “Listen to a successful woman discuss her failure to bear a child…” on the cover was the baby; “Baby Panic” the New York Magazine lamented; and a UK’s Observer ran the article, “When It’s Too Late To Have a Baby.”  Then came the headline-grabbing book, Creating Life, which admonished women to have their kids while young or risk having none at all.  

Here are the results of Dr. Twenge’s search for the “facts” about female fertility: 

The Science

Scientific findings often differ significantly from what the public hears about them.  For example, one widely cited stat that one in three women ages 35 to 39 will not get pregnant after trying for a year that was reported in a 2004 article in the journal Human Reproduction is based on birth records from the years 1670 to 1830.  The fact that the data behind these figures is so outdated is rarely mentioned.

Studies of natural conception are surprisingly difficult to conduct.  Three modern, reliably conducted female fertility studies included only about 400 women 35 or older who might not be representative of all women trying to conceive. One study published in Obstetrics & Gynecology in 2004 examined the chances of pregnancy among 770 European women.  This study found that with sex at least twice a week, 82% of 35-39-year-old women conceived within a year, compared to 86% of 27-34-year-olds, which was almost identical to the fertility of women in their late 20s and early 30s. A 2013 study reported in Fertility and Sterility followed 2820 Danish women as they tried to get pregnant.  When these women had sex during their fertile times, 78% of the 35-40-year-olds got pregnant within a year, compared with 84% of 20-34-year-olds. The scientific data indicates that the ability to get pregnant doesn’t drop off until age 40.  Here’s how Twenge summarizes the data on female fertility:

"In short,  the "baby panic"...is based largely on questionable data.  We've rearranged our lives, worried endlessly, and forgone countless career opportunities based on a few statistics about women who resided in thatched-roof huts and never saw a light-bulb.  In Dunson's study of modern women, the difference in pregnancy rates at age 28 and 37 is only about 4 percentage points. Fertility does decrease with age, bu the decline is not steep enough to keep the vast majority of women in their late 30s from having a child.  And that, after all, is the whole point."

By the way, Dr. Twenge had 3 kids by 40 after deciding at 30 to have a child.

You Can Take Your Time

How long can you safely wait to have a child?  Twenge tells us that the question can’t be answered absolutely for two reasons:  natural fertility data is pretty thin, and statistics only tell you about probabilities and averages—not much use to individuals.  So, what are you to do?

The imperfect data suggests two things: fertility declines with age and most women in their late 30’s will be able to get pregnant on their own.   Twenge says her bottom line is to plan to have your last child by the time you turn 40.  And, she would advise women older than 35 to see a fertility specialist if they haven’t conceived after six months, particularly if the couple has been having sex during fertile times.

There is no perfect time to have a child.  Don’t let alarmist talk about your “biological clock” push you into being a parent before you are ready. Having children when you are young slightly lowers the risks of infertility, but it also carries costs for relationships and careers.

Takeaways

  • Be cautious about metaphors like the “biological clock”—don’t take them literally.
  • The popularity of this metaphor is still strong, and it still supports a traditional view of women.
  • The science does not support the idea that women cannot have children after age 30.
    • The data sets supporting this claim are old or have limited samples.
    • Newer and better science does not support this claim.
    • There is support for having a child until 40.
  • You cannot make individual decisions about having a child on group data.
  • The data sets supporting this claim are old or have limited samples.
  • Newer and better science does not support this claim.
  • There is support for having a child until 40.

References

1.  Weigel, Moira. “The Foul Rein of the Biological Clock.”  The Guardian.  May, 2016. https://www.theguardian.com/society/2016/may/10/foul-reign-of-the-biological-clock

2. Mahdawi, Arwa.  “My Biological Clock is Ticking—But Having Children Seems an Unaffordable Luxury.”  The Guardian.  June 12, 2019.  https://www.theguardian.com/commentisfree/2019/jun/12/biological-clock-ticking-but-having-children-unaffordable-luxury-arwa-mahdawi

3.  Twenge, Jean M.  “How Long Can You Wait to Have a Baby?” The Atlantic.  July/August 2013. https://www.theatlantic.com/magazine/archive/2013/07/how-long-can-you-wait-to-have-a-baby/309374/