Danish researchers found the link between vigorous exercise in early pregnancy and the risk of miscarriage. A study of more than 90,000 pregnant women showed that jogging, playing racket sports and ball games increased the chances of losing babies. However, more gentle exercises such as swimming did not represent the threat of losing pregnancy.

Leisure-time exercises and particularly high-impact exercises were associated with an increased risk of miscarriage in the early stage. Exercises in later stages did not affect the risk.

The women who participated in the study were asked what type of exercise they engaged in at different times during pregnancy. Information was collected about those who had suffered a miscarriage. The risk of miscarriage increased with the amount of exercise. Those women who engaged in more than seven hours a week during weeks 11 to 14 of raised their risk of miscarriage nearly four times. The type of exercise was also significant. Jogging and ball games raised their risk of miscarriage more than four times but low-impact exercises such as dancing or walking doubled the risk too.

However, the increases were from a low base and only around 3.5% of the pregnancies resulted in a miscarriage. Researchers report that these finding should not discourage pregnant women from taking moderate exercise.