Intense Exercise During the First Two Trimesters of Unapparent Pregnancy.

In brief: Two runners who were not aware they had conceived continued their intense running regimens during the first and second trimesters of pregnancy. Both women assumed that their amenorrhea was due to endurance training. When their pregnancies were diagnosed, both women markedly reduced their training mileage during the third trimester because they feared that intense exercise might harm the fetus. Retrospective data were collected on their antenatal and intrapartum courses. Both women delivered healthy infants of normal weight. Although these two cases suggest that strenuous anaerobic exercise during pregnancy is not harmful, more studies are needed to determine if these cases are isolated.