Running in pregnancy does not lead to lower birthweight or premature birth, new study finds

Researchers in the UK have published their findings of a study that looks at the effects of running during pregnancy and the risk of premature birth and low birthweight. Until now, the impact of recreational running on pregnancy has been largely unknown. With 60% of half-marathon runners known to be women, and a majority of recreational runners at childbearing age, this study was one of the largest of its kind.  

During the study, 1293 female participants were recruited from Parkrun, a non-profit organisation that regularly puts on 5km runs across the UK. Women were divided into groups depending on whether they continued to run throughout pregnancy, their weekly kilometres if they continued to run, and in which trimester they stopped running.

The researchers found that 45% of the participants chose not to run during pregnancy, 15% stopped during their first trimester, 25% ran into their second trimester, and 16% ran into their third trimester. They found that most babies were born at full term and that there was no difference in rates of premature birth and low birthweight between the runners and non-runners.

Related: New study finds exercising during pregnancy can reduce the duration of labour

The researchers did find that assisted vaginal delivery was around 5% higher in the women who had continued to run during pregnancy, however it is difficult to conclude whether this is a direct result of running alone. The researchers noted this was “possibly due to increased pelvic floor muscle tone”, however more analysis is needed to draw any conclusions.

According to the NHS, the current guidelines in the UK say that continuing with 30 minutes of moderate daily exercise is safe for most pregnant women. Until now, high-impact exercise such as running has not been recommended during pregnancy, yet it is important to note that this study was conducted on women who already regularly took part in Parkruns’ – they were already runners. The NHS guidelines recommend that during pregnancy, you should “keep up your normal daily physical activity of exercise”, or in other words if you're not already a runner, don't start during pregnancy. 

Whilst the findings are encouraging and call into question previous studies that have raised concerns on the harmful effects of running during pregnancy, it cannot be applied to the general population just yet. The study only looked at women who were already regular runners and who would generally have had higher fitness levels and a healthier lifestyle. Furthermore, due to the observational style of the study, cause and effect cannot be proven, and further research will need to be conducted to determine the true effects of running.

Whether you’re a runner or not, it is always a good idea to speak to your GP or midwife about your exercise plan when pregnant.