Fertility: What Historical Data Can’t Tell You

This story came across my Twitter feed today:

How Long Can You Wait to Have a Baby? – Atlantic Mobile http://t.co/SLgYCPaJ5P

— Jamie Gravell (@Dontworryteach) August 10, 2013

In the linked article at The Atlantic, How Long Can You Wait to Have a Baby?, which is mostly about modern women’s anxieties and experiences regarding getting pregnant in their thirties, I came across a singular, an astonishing factoid that illustrated how history is horribly misused by other researchers:

The widely cited statistic that one in three women ages 35 to 39 will not be pregnant after a year of trying, for instance, is based on an article published in 2004 in the journal Human Reproduction. Rarely mentioned is the source of the data: French birth records from 1670 to 1830. The chance of remaining childless—30 percent—was also calculated based on historical populations.

In other words, millions of women are being told when to get pregnant based on statistics from a time before electricity, antibiotics, or fertility treatment. Most people assume these numbers are based on large, well-conducted studies of modern women, but they are not. When I mention this to friends and associates, by far the most common reaction is: “No … No way. Really?”

Now, I’m going to set aside the whole broad swipe that statistics about childbearing before electricity must be inherently problematic to say that my concern, as a historian, takes a different tangent. I followed up on that lead, found and read the article in question by Henri Leridon, “Can assisted reproduction technology compensate for natural decline in fertility with age? A model assessment” Human Reproduction 19:7 (2004), 1548-1553. Leridon explains that he relies upon a 1961 study for the historical data and reveals some interesting assumptions imbedded into that analysis:

It can be assumed that fertility control did not exist in these populations, or that if it existed it was fairly ineffective (except in a small proportion of the population, such as prostitutes or highly educated women). This situation was called ‘natural fertility’

You know what we say about assumptions, don’t you? They make an ass out of “u” and me, only, in this case, I’m reserving the scorn for the medical researchers hijacking historical material in pursuit of a biologically “natural fertility”. Other historical scholars have long been showing that premodern societies were not artless, especially when it came to childbearing. To the contrary, reproduction was a fraught and tightly managed part of human society, going back millennia. Take a look at Angus McLaren’s magisterial overview from 1992 A History of Contraception: From Antiquity to the Present Day (Oxford: Blackwell, 1992) or any one of a dozen or more works in demography, gender studies and other related fields which demonstrate that early modern Europeans practiced family planning and regularly procured early-term abortions.

This historical data set from early modern France cannot and should not be used to document the “natural fertility” level of women at various ages. Pregnancy and reported childbirths were already being shaped by the traditions of marriage, concepts of legitimacy and socio-economic factors. Even if early modern contraceptives and abortifacents were much less effective than modern medications, we still haven’t tackled the question of agency.

How many of these women in the records desired children? How many had other, underlying conditions that might have interfered with pregnancy? How many were living apart from partners? How many breastfed and how many didn’t? How many struggled with starvation and malnutrition which compromised their ability to reproduce? These are all factors that can greatly alter the outcomes from what one might expect would be a basic biological record and they’re just a few of the elements at play in the complex realities of early modern France.

Colour me appalled that this old and wrong-headed historical conflation of early modern birth records with “natural fertility” data is still powering twenty-first century fertility science. I sure as heck hope some medical researcher is pursuing a much better baseline for “natural fertility” than digging through our historical databases in hopes that olden-days people are just the same as laboratory control groups!