Letter to the Editor: Does exercise training during pregnancy affect gestational age?

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By Adriana Suely de Oliveira Melo, MD, MSc et al.

Barakat et al. 1 have presented us with a paper of excellent methodological quality, following all the steps recommended in the Consolidated Standards of Reporting Trials (CONSORT) and dealing with a question that never fails to generate controversy with respect to the practice of physical activity during pregnancy: prematurity. nother strong point of the paper is the fact that the physical exercise was systematized and monitored, guaranteeing that the pregnant woman indeed followed the prescribed program.

Various controversies continue to surround the topic of physical exercise and pregnancy and the real effects of exercise on the conceptus remain to be clarified. The spectrum of these effects ranges from fetal growth to the duration of the pregnancy, with some studies associating prematurity and growth restriction with the practice of physical exercise 2-4. Despite these speculations, until recently no randomized clinical trials (RCT) with adequate sample sizes had been identified in which pregnant women were systematically followed up for a period encompassing the second and third trimesters.

The excellent quality of this paper prompted us to examine it in detail in an attempt to understand some points that we would now like to put to the authors. Since the objective of the RCT was to evaluate the risk of premature labor, would it not have been better to have excluded all the pregnant women with a history of premature labor in view of the fact that the results show that one of the cases of prematurity in the intervention group was precisely due to a prior history of prematurity?

Another point that drew our attention concerns the exclusions in both groups, which were the result of various situations that may have affected the outcome “gestational age”, such as bleeding, pregnancy-induced hypertension and threatened preterm labor. In our opinion, these women should have continued in the study and an intent-to-treat analysis should have been carried out. We were also intrigued by the fact that one patient was excluded because her pregnancy was a twin pregnancy. Was a single pregnancy not one of the inclusion criteria?

It may perhaps have been interesting NOT to have included women with a history of premature delivery. Although the inclusion criteria accepted the possibility of the participants having had at the most one previous premature delivery, this may have had an effect on the mean gestational age reported in the present study.

We were unable to identify in the paper any description of the parameters used to calculate sample size to determine whether the final number of participants included was sufficient to demonstrate any
differences between the groups. Could a type II statistical error have occurred?

Another minor question we would like to pose is whether the intensity of the prescribed exercise was light-to-moderate or moderate, since it is described in different ways in the various sections of the manuscript and it is known that some outcomes are dependent on the intensity of exercise.

Finally, we would like to know whether the authors have data on other gestational or perinatal outcomes, since such a well-conducted RCT as this one should have generated interesting results that deserve to be published.

1. Barakat R, Stirling JR, Lucia A. Does exercise training during pregnancy affect gestational age? A randomised controlled trial. Br J Sports Med 2008; 42(8):674-8.

2. De Ver Dye T, Fernandez ID, Rains A, Fershteyn Z. Recent studies in the epidemiologic assessment of physical activity, fetal growth, and preterm delivery: a narrative review. Clin Obstet Gynecol 2003; 46(2):415-22.

3. Grisso JA, Main DM, Chiu G, Synder ES, Holmes JH. Effects of physical activity and life-style factors on uterine contraction frequency. Am J Perinatol 1992; 9(5-6):489-92.

4. Misra DP, Strobino DM, Stashinko EE, Nagey DA, Nanda J. Effects of physical activity on preterm birth. Am J Epidemiol 1998; 147(7):628-35.

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