Pregnant women can be given all sorts of strange advice when friends and family find out they are expecting a child.

While it is often well-meaning, however, in many cases, these tips have little scientific basis. Here we look at three of the most persistent myths.

Eating for two

Disappointingly, it doesn’t take many extra calories to feed a growing foetus. Even in the third trimester, on top of the usual daily recommendation of 2,000 calories, women only need an extra 200 calories a day. That’s the equivalent of a bagel or a heaped tablespoon of mayonnaise, so hardly a feast. 

Women can even follow a diet plan without harming their babies. In fact, healthy diets not aimed at weight loss have been found to bring benefits for the mother and the baby. A meta-analysis of 44 randomised controlled trials, where the data from more than 7,000 women was taken, combined and re-analysed, found that those who were given a diet plan to follow gained on average 3.84kg (8.4lbs) less by the end of their pregnancy than women in control groups.

In these studies, some women were given a conventional balanced diet, others a low glycaemic diet. This made no difference to the weight of their babies at birth, but crucially, reduced the risk of pre-eclampsia, a blood pressure disorder that is one of the most common complications of pregnancy.

Period pains disappear

Spending a day a month clutching a water bottle to your abdomen will be a thing of the past once you’ve had a baby – or that’s what we’re told. The amount of pain, if any, that women get during their period varies a lot between individuals, with a lucky half of the female population rarely or never experiencing period pain. For those that do, it’s reassuring to think that once they’ve had a baby there will be no more pain, but it might not be as simple as that.

A study of women over the age of the 40 found that as they got older their pain decreased, even though none of them had had children

The severity of period pain does change over the years, often lessening with age. This is frequently assumed to be because many women have children. But in 2006, a team in Taiwan conducted a study of women over the age of the 40, finding that as they got older their pain decreased, even though none of them had had children. This raises the question of whether it’s age or giving birth that makes the difference.

To try to establish what’s happening, the same team of researchers followed more than 3,500 women for eight years. During that time, some had children and many did find their period pains lessened after they had given birth, but it didn’t work for everyone. Of those who had a caesarean section, 51% were still dissatisfied with the level of period pain afterwards and even in those who had vaginal births, 35% found they still got period pain. Length of pregnancy also made a difference, with 77% of mothers of premature babies still experiencing pain.

So, childbirth does help some women with period pains, but unfortunately not all of them. The researchers speculate that vaginal births might be more effective at reducing later pain because pelvic floor injuries might damage the nerves linking the uterus to the brainstem, meaning the pain can’t be felt. They also wonder whether vaginal births might lead to the lining of the womb releasing lower levels of potentially pain-inducing prostaglandins compared to a caesarean or premature birth.  

The authors suggest that those who still experience period pains, even after a vaginal birth, might have an underlying condition causing the pain, such as endometriosis. But the first genome-wide association study, conducted in 2016 suggests yet another factor contributing to the severity of period pain. If your period pain is bad, it’s partly down to your genes.

Avoid flying

Airlines stop women from flying towards the end of their pregnancy, not because it is dangerous for the developing foetus or the mother, but in case they go into labour on board, which isn’t good for anyone involved.

When it comes to early pregnancy, most of the research comes from studies of flight attendants, rather than passengers. A Finnish study conducted in 1999 caused alarm bells to ring. It looked back over many years of data and found attendants flying between 1978 and 1994 did have a slightly increased risk of miscarriage, but curiously those flying between 1973 and 1977 had a slightly decreased risk.

Even in the years where an increased risk was found, it wasn’t clear whether this was due to an aspect of flying or to the demands of the job

Even in the years where an increased risk was found, it wasn’t clear whether this was due to an aspect of flying or to the demands of the job. Indeed, when a large group of flight attendants were compared with a group of teachers in 2015, their risk of miscarriage was no higher.

When the researchers examined the records of two million flights flown by 673 flight attendants and looked at the shift patterns in detail, they found that those who experienced the greatest sleep disruption had a higher miscarriage risk than flight attendants with easier shift patterns.

So once again it doesn’t seem to be flying itself that’s a problem, but the disruption to the natural circadian rhythms that control when we sleep.

Of course, most women don’t fly nearly as often as flight attendants, so the consensus is that flying in pregnancy is safe for most people. In 2002 the American College of Obstetricians and Gynecologists published guidance saying just this, but concluded that women with pregnancy-induced high blood pressure, an increased risk of premature labour, or poorly controlled diabetes, should get advice from their doctor before flying. Any women with medical problems exacerbated by low oxygen levels should consider taking oxygen with them.

In the UK, the Royal College of Obstetricians and Gynaecologists advises taking regular walks around the plane and keeping hydrated to lower the risk of deep vein thrombosis, but again stresses that there is no evidence that flying causes miscarriage or early labour.

So, it seems that some of the advice commonly given to women when they fall pregnant may not be as sound as it could be. It’s probably best not to overeat, feel free to go on planes if you want to, but don’t assume that after it’s all over and your baby is born, that period pains will be a thing of the past. They might disappear, but then again, they might not.

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