Pregnancy really does cause "baby brain" according to new Australian research

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So-called “baby brain” refers to increased forgetfulness, inattention, and mental “fogginess” reported by four out of five pregnant women. These changes in brain function during pregnancy have long been recognised in midwifery folklore, but a new study, Cognitive impairment during pregnancy: a meta-analysis, has confirmed “baby brain” is a very real phenomenon, and also affects several cognitive areas.

The researchers combined data from 20 studies reporting the relationship between pregnancy and brain changes. They then pooled these differences together to assess the cognitive functioning of 709 pregnant women and 521 non-pregnant women. The study, published in The Medical Journal of Australia (available on CKN), is the first to explore how pregnancy may affect other cognitive areas beyond memory and to look specifically at how these changes might vary according to pregnancy trimesters.

What the researchers found

The results of the study showed that when pregnant women are compared to non-pregnant women, they perform much worse on tasks measuring memory and executive functioning (which includes attention, inhibition, decision-making and planning), and this difference is most pronounced during the third trimester. Women were tested with tasks such as the digit span test, which involves remembering digits in a line. When the same women were tested at multiple points during their pregnancies, the decline appeared to start during the first trimester, then stabilise from the middle to the end of the pregnancy.

The researchers warned that their results should be interpreted with caution, given that the cognitive function of pregnant women remained within the normal range.

“Given the small to moderate effect sizes of the differences and the limited number of longitudinal studies available, our findings need to be interpreted with caution, particularly as the declines were statistically significant, but performance remained within normal ranges of general cognitive functioning and memory,” they wrote.

Lead author Sasha Davies, a PhD candidate at Deakin University, said that the degree of cognitive impairment found in the study was not extreme and usually only noticeable to the woman herself, and perhaps her partner.

“So as much as you might see a small cognitive decline, it’s not going to be anything that is very drastic,” Ms Davies said. “We don’t think it’s going to affect their professional lives or their personal lives.”

"It’s important to note that while we found differences, the pregnant women were still broadly performing in the normal range, albeit at the lower end, particularly for memory tasks. So while some pregnant women may notice they don’t feel as “sharp” as usual, these effects are realistically not likely to have any dramatic impact on everyday life. Instead, some women will simply find it seems to take more mental effort to do tasks that were previously routine. These changes might be noticeable to people very close to them such as family or friends, but this is highly dependent on each woman’s personal experience of pregnancy," she said.

Ms Davies said that researchers were yet to identify the mechanisms responsible for the change. She said factors such as hormone levels, stress, anxiety and mood changes had been suggested in other studies.

“We know that all those factors have an impact on cognition in other groups, but we don’t know that that’s the key reason for this change that we see in pregnancy,” Ms Davies said.

What causes baby brain?

There’s still a lot of speculation about what might cause “baby brain” and there is a long way to go before finding definitive answers.

An intriguing study published last year in Nature Neuroscience showed there were reductions in grey matter in the brains of pregnant women in regions known to be closely tied to processing social information, such as decoding infant facial expressions and establishing healthy bonding between mum and baby.

This presents a compelling idea that “baby brain” is actually an important adaptive phenomenon that might help women prepare for raising their children by allowing the their brains to adapt to their new role as mothers. Importantly, this same study showed losses of grey matter in the hippocampus, an area of the brain responsible for memory function, are restored two years after the birth of a child. This supports the idea cognitive declines are not permanent.

There are still several questions that will need to be answered vefore we understand more about this phenomenon. First, postpartum measures of cognitive functioning are frequently not included when exploring cognition and pregnancy. This means it’s unclear whether the changes seen during pregnancy extend into early parenthood and, if so, how long they might last.

Second, the underlying mechanisms of this relationship are still open to speculation. Given women experience huge hormonal shifts during pregnancy, it’s likely increases in hormones oestrogen, progesterone and oxytocin play an important role in facilitating these cognitive changes.

Other factors may also contribute, such as disrupted sleep patterns, mood changes, increased stress levels, and morning sickness – all of which are natural experiences of pregnancy. After all, pregnancy is a time of massive physical, psychological, and social change, so it isn’t surprising this is distracting.

What can pregnant women do about it?

Co-author Associate Professor Linda Byrne, Deputy Head of the School of Psychology at Deakin University, said that there were several steps that women could take to minimise the impact of these cognitive changes in pregnancy.

“Fatigue often plays a big part in our cognitive functioning, so sleep hygiene is really important, particularly in the first and last trimesters. In the first trimester when you have the massive surge of hormones and you’re feeling unwell, and in the last trimester when you’re large and uncomfortable, those are the two periods when people tend to report more fatigue. So, making sure that you’re well rested, that’s going to improve your cognitive abilities,” she said.

Maintaining good nutrition and exercise habits were also important, Professor Byrne said. She also advised women to make use of memory aids, such as phone apps and reminders.

“Even for people who once relied upon their memory quite easily, making lists and writing reminders is a good way of just making sure that if there are important things, then we are not going to miss those.”

Adapted from MJA Insight and The Conversation.
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