Most health advice for pregnant women is uncontroversial: to stop smoking, eat a healthy diet and take folic acid.
However, recommendations for exercise vary. Some women are advised to refrain from exercise due to the possibility of risk; these include women with abnormally located placenta, ruptured membranes, twins, women with a short cervix or those at high risk of preterm labour.
Healthy pregnant women (those lacking risk factors) are often told that exercise is ‘good for them’ and advised to exercise to tolerance, and to avoid activities that are too strenuous or those that could result in reduced blood flow to the baby in later pregnancy, like lying on one’s back.
But what activities are too strenuous? Fitness enthusiasts weight-lifting while 32 weeks pregnant provoke criticism for risking harm to their baby. (I eagerly await the trial that looks at this subset of pregnant women.) So far, though, very little evidence exists that documents harm to either mother or baby, even when considering highly strenuous exercise of the kind undertaken by pregnant Olympic athletes.
While the two papers above suggest that exercise in excess of 90 per cent of maximum recommended heart rate may be potentially harmful, the study numbers were too small to draw any meaningful conclusions. Furthermore, most pregnant women won’t exercise to this high level of intensity.
No evidence exists to support the contention held by some people that exercise in the first trimester of pregnancy may increase the risk of miscarriage.
How about the benefits of exercise? Traditional teaching holds that exercise, particularly walking in the late third trimester, can bring on labour and indeed shorten the duration of labour. Clinical work has suggested that walking may be of benefit once labour has started but there is no evidence to recommend walking as a method of inducing labour.
In terms of other benefits, a new meta-analysis has documented multiple benefits of exercise in pregnancy, including lower rates of preeclampsia, hypertension, gestational diabetes, excessive weight gain and low birth-weight babies, all of which may cumulatively reduce the incidence of caesarean section, the risk of which is elevated by the presence of any of the above conditions.
New evidence also suggests that exercise may have a direct role in decreasing the incidence of caesarean section.
In summary, exercise represents a simple, inexpensive intervention that, embarked upon following medical advice, can have profound effects on a woman’s risk profile with directly observable benefits.