How Long Can You Wait To Have a Baby?

In an article entitled “How Long Can You Wait to Have a Baby?” published in The Atlantic in the summer of 2013, Jean Twenge describes her fear of waiting to have children till her later 30s based on the widely heralded message in the media that 1 in 3 women over the age of 35 will not be able to conceive after a year of trying.

She goes on to suggest that such statistics derive from populations of women studied prior to the 20th century and that current studies are much more optimistic about a woman’s fertility in her later 30s, thus encouraging women not to worry so much about the purported age-related decline in fertility.

As a Reproductive Endocrinologist and as a woman in my mid-30s, I read this article with mixed emotions. Certainly, I don’t think that women should be pressured into trying to get pregnant before they are ready. On the other hand, I think the notion that there is no need to worry as long as you try to have children before age 40 is somewhat dangerous.

Certainly, the percentage of women we see in our infertility practice who are younger than 40 with age-related fertility issues is high (and Twenge is correct on her assumption that fertility specialists are biased with respect to infertility risks—pretty much all of the women we see are infertile!). So what’s the truth with respect to age-related fertility decline?

Statistics show a natural fertility decline with age

The often quoted statistic that 1 in 3 women over age 35 will have trouble getting pregnant derives, at least in part, from studies published in the 1950s done on the Hutterite population, a Protestant sect in the Dakotas, Montana and Canada where the practice of contraception was condemned by religion (1).

Studying fertility rates in the general population is quite difficult, due to varying use of contraception, decline in sexual activity with age, etc. So studying a population where contraception is not used and having a large family is highly valued (women in this sect are pregnant, on average, 10 times during their reproductive years) gives us an idea of when natural fertility starts to decline.

In this population, 33 percent of women had their last pregnancy between the ages of 35 and 39, suggesting that it is in this window when they reached the end of their natural fertility. Furthermore, in a study published in 1991 in the British Medical Journal, the pregnancy rate of women who were undergoing insemination with donor sperm because their husbands were completely infertile (effectively eliminating any confusion surrounding use of contraception, male factor infertility and timing/frequency of intercourse) demonstrated that after age 31, the chance of conception falls by about 12 percent each year (2).

Finally, in the very study by Dunson and colleagues published in 2004 that is quoted by Twenge herself, 18 percent of women age 35-39 fail to conceive after one year (compared to 8 percent of women age 19-26) (3). And for women ages 35-39 who are married to a male partner who is 40 (not an uncommon scenario), the risk of infertility after one year of trying increases to 28 percent.

This statistic is surprisingly similar to the 1 in 3 statistic we see with the Hutterite population, suggesting that although our culture has progressed by leaps and bounds since the 1950s, with women climbing the corporate ladder—and delaying motherhood to do so, our ovarian biology has sadly not kept up.

Not waiting to have a baby is not always a realistic option

Don’t get me wrong; I do agree with the overall message that Twenge puts forth, which is that the majority of women who try to get pregnant in their later 30s probably will. What I don’t agree with is having the attitude that age-related fertility decline is not something to worry about. At the end of the day, it doesn’t matter what study you choose to believe and whether 1 in 3 women or 1 in 5 women between the ages of 35-39 will have trouble conceiving. If you are that 5th woman, dealing with infertility will be a 100 percent reality for you.

In her article, Twenge references the book Creating a Life, by Sylvia Ann Hewlett, that advises women to have children in their younger reproductive years or risk not being able to have them at all and the media publicity sparked by the book in magazines such as Time and The New Yorker. At the end of her article (my favorite part), Twenge describes a particularly amusing SNL skit that arose from this media attention, where Tina Fey discusses the book on a “Weekend Update,” saying that “according to author Sylvia Hewlett, career women shouldn’t wait to have babies, because our fertility takes a steep drop-off after age 27. . .and Sylvia’s right; I definitely should have had a baby when I was 27, living in Chicago over a biker bar, pulling down a cool $12,000 a year.

That would have worked out great.” To which Rachel Dratch, also in the skit, responded, “Yeah. Sylvia, um, thanks for reminding me that I have to hurry up and have a baby. Uh, me and my four cats will get right on that.” And finally, from Amy Poehler’s character, “My neighbor has this adorable, cute little Chinese baby that speaks Italian. So, you know, I’ll just buy one of those.”

Although I find the dialogue in this skit to be hilarious, the point being made is that it is frustrating for women to hear about fertility decline when it is not a realistic option for most women to stop whatever they are doing in their lives and have a baby, whether it be career-related, finance-related, or due to not having an appropriate partner. However, a lot has changed since Tina Fey and colleagues poked fun at this issue on SNL in 2002.

As of about 18 months ago, egg freezing is no longer considered an experimental technique, and more and more women are considering this as a means to help protect against age-related fertility decline. At the end of the day, I agree that the message we want to send to women about their fertility should not be one shrouded in fear and warnings, but one that empowers women to understand their reproductive biology and fertility window, and to make proactive decisions at appropriate time points about when and how they may choose to have a family.


References:
1) Tietze C. Reproductive span and rate of reproduction among hutterite women. Fertil Steril, 1957; 8(1): 89-97.
2) Van Noord-Zaadstra BM, Looman CWN, Alsbach H, Habbema JKF, te Velde ER, Karbaat J. Delaying childbearing: effect of age on fecundity and outcome of pregnancy. BMJ, 1991; 302: 1361-5.
3) Dunson DB, Baird DD, and Colombo B. Increased infertility with age in men and women. Obstet Gynecol, 2004; 103 (1): 51-56.