Chahal et al. Respond to “Physical Exertion and Placental Abruption”

We appreciate the thoughtful comments by Baylin and Guyer (1) on our article, in which we evaluated the acute risk of placental abruption following physical exertion (2). Their commentary raises important issues on the etiology of placental abruption, the clinical implications of our work, and the most appropriate public health message regarding physical activity during pregnancy. Baylin and Guyer suggest a few interesting precipitants of myocardial infarction that may also increase the acute risk of placental abruption, such as cocaine use, sexual activity, and anger. We agree that these are important questions for future studies to investigate. Cocaine use over the course of pregnancy increases the baseline risk of placental abruption as well as other adverse obstetrical outcomes (3). Given the fast-acting vasoconstrictive effects of cocaine, it is possible that its use would also increase the immediate risk of placental abruption. The association of sexual activity and a transiently increased risk of cardiovascular events has been well-documented using the case-crossover approach (4), and we think this exposure would be particularly interesting for obstetrical outcomes; not only does sexual activity include physical exertion, but vaginal-penile intercourse may cause oxytocin release and uterine contractions from direct stimulation of the lower uterine segment, orgasm, and the high prostaglandin content found in semen (5). While we present an increase in the acute risk of placental abruption following physical stress, and others have found a higher risk following exposure to chemical stress (6, 7), the immediate effect following psychological stressors is, to our knowledge, unstudied. Anger is another important exposure because its physiologic effects are similar to those of heavy physical exertion (8). A case-report suggests that panic may be a potential stressor as well (9). Baylin and Guyer comment that the risk associated with episodes of physical exertion among women who were less sedentary in our study was not null but hypothesize that a null association might be found among women who are more physically active, similar to prior studies on myocardial infarction. We think this is possible as well, given that the circulating level of catecholamines correlate better with the relative intensity of exertion than with the absolute intensity and that catecholamine release is reduced after exercise training (10). Finally, we agree that the public health implications of these findings need to be addressed thoughtfully. In this case-only design, we studied 663 women who had had placental abruption and were therefore, by definition, delivering high-risk pregnancies. The majority of pregnancies do not experience this rare complication, and women with uncomplicated pregnancies ought to be encouraged to engage in safe levels of physical activity before, during, and after pregnancy. As we stated in our study, although we did not compare women who had placental abruption with those who did not, we also hypothesized that women who engaged in more physical activity would have a lower total risk of placental abruption despite the transient increase in risk associated with each episode of exertion, similar to the relationship between physical exertion and ischemic cardiovascular events. Author affiliations: Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts (Harpreet S. Chahal, Bizu Gelaye, Michelle A. Williams); Mississauga Academy of Medicine, University of Toronto Mississauga, Mississauga, Canada (Harpreet S. Chahal). Conflict of interest: none declared.

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