Pregnancy Doesn’t Actually Make Women Dumber

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Oh my gosh, I think my brain is permanently shrunk after having three kids,” CBS Early Show host Hannah Storm once said. In a diary for New Statesman, Sarah Montague, who co-hosts the BBC’s flagship Today news program, said: “My biggest worry has been what you might call ‘preg-head.’” 

Storm and Montague believe they were suffering from a kind of mental impairment brought on by the biological changes associated with pregnancy — an idea that’s been called preghead, pregnesia, momnesia and baby-brain. Anecdotal evidence for the condition is everywhere and frequently shared by writers and broadcasters. The idea has even been endorsed by respected health authorities in the UK. An NHS pamphlet published in 2005 on “50 things would-be fathers should know,” put it this way: “Pregnant women are a bit vague … it’s their hormones.”

Surveys suggest that belief in pregnesia is widespread among the public. In 2008, Ros Crawley at the University of Sunderland quizzed dozens of pregnant and non-pregnant women and their partners, and found that they all agreed that pregnancy is typically associated with cognitive decline.

Given these views, perhaps it’s no wonder that researchers have uncovered disconcerting evidence about the prejudice shown toward pregnant women, especially in work contexts. Although such prejudice is driven by multiple factors, widespread belief in baby-brain likely plays an important part. Consider a study published in 1990, in which Sarah Corse at the University of Pennsylvania invited male and female MBA students to interact with a female manager they’d never met before, and then rate her afterward. In fact, the “manager” was a research assistant acting the part, and the key finding was that students given the additional information that the woman was pregnant reported finding their interaction with her less satisfying than students not fed this lie.

The myth of the baby-brain hasn’t come out of thin air. Countless surveys of pregnant women, using questionnaires and diary reports, have found that many of them — usually about two-thirds — — feel that being pregnant has affected their mental faculties, especially their memories. Of course, that doesn’t mean that it has. Neither does it prove that the cause is some biological consequence of the state of pregnancy as opposed to lifestyle factors, like fatigue and stress.

The most dramatic claim about the biological effect of pregnancy on the brain is that it causes shrinkage (as mentioned by the CBS host Hannah Storm). Given how drastic this sounds, you’d think it would be backed up by plenty of evidence. In fact, the idea is based almost entirely on a small study published in 2002 by researchers at Imperial College School of Medicine in London. Angela Oatridge and her colleagues scanned the brains of nine healthy pregnant women and five pregnant women with preeclampsia (a condition associated with high blood pressure), finding evidence of brain shrinkage of between 2 to 6.6 percent volume during pregnancy that was reversed six months after giving birth. But without replication and a larger sample, it’s difficult to take this single study too seriously.

Returning to the issue of cognitive impairment, whereas subjective reports of this from pregnant women are widespread, objective laboratory studies are far less consistent. For many years, for every study that turned up an apparent impairment in memory, another was published that drew a blank. Some experts believed this was a sign that the effect is unreliable and small; others said it was simply due to different labs using different methods.

An attempt to weigh all the evidence and get to the truth was published in 2007 by Julie Henrey of the University of New South Wales in Sydney and Peter Rendell at the Australian Catholic University in Melbourne. They conducted a meta-analysis that gathered all the evidence from 14 studies published over 17 years. Their conclusion? There is a real effect of pregnancy on women’s cognition, but it’s a “relatively subtle” one, “relatively small in magnitude,” and it manifests most noticeably during tasks that require executive functioning — that is, juggling lots of information at once.

Unfortunately, Henry and Rendell’s abstract (the summary) of their paper was worded in a way that proved ripe for misinterpretation. They wrote, “The results indicate that pregnant women are significantly impaired on some, but not all, measures of memory.” By “significant” they meant statistically significant: that is, unlikely to be due to chance. But journalists worldwide misunderstood the research summary and the public message became sensationalized: “many [pregnant] women … suffer considerable memory loss” (The Observer; emphasis added) and “pregnant women were considerably impaired (Hindustan Times; emphasis added).” These are just two examples of many.

Since that meta-analysis, the literature has taken a number of further twists and turns. An Australian study published in 2010 was superior to many of its predecessors in following a large group of women over time and testing their cognitive abilities, including working memory and processing speed, prior to pregnancy, during, and after. And a handful of other studies found associations between memory and pregnancy. But then again, Helen Christensen and her colleagues found no evidence of pregnancy being associated with cognitive decline.

Still, taken altogether, it looks as though pregnancy really is associated with cognitive changes in some women, including memory problems. The inconsistent results could be a consequence of different methods used and how relevant the tests are to real life. But this prompts an obvious question — if baby-brain is a genuine phenomenon, why should female humans have evolved to be mentally impaired just when you’d think they’d need to be at their most alert?

Because the cognitive problems associated with human pregnancy are all the more mysterious in light of research with rats and other mammals that suggests pregnant females undergo cognitive enhancements, not impairments, that stay with them into motherhood. A pioneer in this field is Craig Kinsley at the University in Richmond. He told me in 2010: “Our [maternal] rats get better at virtually everything they need to, to successfully care for their expensive genetic and metabolic investments. Foraging, predation, spatial memory all improve; stress and anxiety responsiveness decreases.”

When I asked Kinsley why the human literature was full of findings about cognitive impairments while the animal research points to improvements, he said the disparity may have to do with the kinds of tasks and behaviors that were being studied in humans. “Much of the data from human mothers has been derived from asking females to demonstrate cognitive enhancements to skills, behaviors, occupations that are largely irrelevant to the care and protection of young,” he said. Another suggestion is that the baby-brain in humans is a side effect of the dramatic changes underway in mothers’ brains that are gearing them up for the demands that lie ahead. Framed this way, it’s the price that’s paid for what is ultimately a maternal neuro-upgrade.

Recently, a spate of human studies has been published that may be hinting at these maternal advantages. For instance, James Swain’s lab at the University of Michigan has shown how several areas in the brains of new mothers are especially responsive to the sound of their own baby crying, compared with the sound of other babies’ cries. Regarding physical brain changes, a team led by Pilyoung Kim at Cornell University and Yale University School of Medicine scanned the brains of 19 new mothers in the weeks immediately after giving birth, and then again several months later. The later scan showed increased volume in a raft of brain areas that are likely to be involved in mothering activities — the prefrontal cortex, parietal lobes, hypothalamus, substantia nigra, and amygdala.

And in 2009 and 2012, labs at the University of Bristol and Stellenbosch University, respectively, reported evidence that pregnant women have a superior ability to determine whether a face is angry or fearful, and they show heightened attention to fearful faces. The Stellenbosch team wrote: “Heightened sensitivity to danger cues during pregnancy is consistent with a perspective that emphasizes the importance of parental precaution and the adaptive significance of responding to potentially hazardous stimuli during this period.”

More findings like these are bound to appear as researchers begin to test pregnant and recently pregnant women on behaviors that are directly relevant to raising a child. That pregnancy has a profound effect on the brain and mental function of women seems increasingly certain. But the idea that it’s a purely negative effect is a myth that’s in the process of being debunked. Any pregnancy-related impairments are likely a side effect of what ultimately is a maternal neuro-upgrade that boosts women’s ability to care for their vulnerable offspring. Many will welcome the demise of the baby-brain myth, because it’s a simplistic, one-sided concept that almost certainly encourages prejudice against women. 

This article is adapted by permission of the publisher John Wiley & Sons Ltd., from Great Myths of the Brain, by Christian Jarrett. Copyright 2014, 2015, by Christian Jarrett.