Alpha-fetoprotein, prolactin and cortisol responses to maximal exercise during pregnancy.

The purpose of this study was to assess the maternal-fetal hormonal stress reactivity, via the monitoring of alpha-fetoprotein (AFP), prolactin and cortisol responses, to maximal maternal exercise. We had women perform maximal exercise bouts to volitional fatigue at select times in their gestation (25 weeks, 35 weeks, and 10 weeks post-partum). Blood samples were taken immediately before exercise and 1 min into the recovery from exercise. Each subject's prior diet, physical activity, and time of day for the exercise trials were held consistent. Exercise caused significant reductions in AFP at both 25 and 35 weeks of gestation. Prolactin decreased significantly after exercise at 35 weeks and tended to do so at 25 weeks. No significant change in prolactin was noted for the post-partum trial. Similarly, cortisol also showed reductions after exercise at 25 weeks and 35 weeks of gestation but tended to increase at the post-partum trial. The prolactin and cortisol responses during gestation are contrary to accepted non-pregnancy responses. These changes may be related to an altered regulatory axis, metabolic clearance rate, and/or capillary fluid movement. We conclude that 1) fetal to maternal bleeding in response to maximal maternal exercise is not evident immediately post-exercise and 2) an alternation in the normal endocrine stress response to exercise may occur during pregnancy.