Safety of high-intensity functional training (CrossFit) during pregnancy: A retrospective cohort study

Regular physical activity (PA) during pregnancy is associated with lower risks of gestational diabetes, hypertensive disorders, and excessive gestational weight gain, as well as improved neonatal outcomes. Current guidelines recommend moderate-intensity exercise, however, evidence regarding the safety of high-intensity functional training modalities, such as CrossFit remains limited, leading to ongoing concerns about potential maternal and fetal risks.

To evaluate the safety of CrossFit training during pregnancy, using gestational age at delivery as the primary outcome, and to compare maternal and neonatal outcomes between women who continued CrossFit and those who did not.

We conducted a retrospective cohort study at a tertiary medical center in Israel. The study was powered to detect a two-week difference in gestational age at delivery, requiring enrolment of 132 participants. Pregnant women who engaged in CrossFit training, at least twice weekly throughout the third trimester (n = 44) were compared with age- and parity-matched controls (n = 88). Data were extracted from maternal delivery and neonatal discharge records, as well as from questionnaires completed by the participants regarding physical activity-related aspects. The primary outcome was gestational age at delivery. Secondary outcomes included birth weight, birth weight percentile, maternal complications, and adverse neonatal outcomes. Statistical analyses included independent-samples t-tests, chi-square tests, and logistic regression. Multivariable logistic regression adjusted for maternal age, parity, diabetes, and hypertension was performed to assess the odds of preterm birth (<37 weeks).

A total of 132 women were included in the analysis (44 who continued CrossFit training and 88 controls). Gestational age at delivery did not differ significantly between groups (39.3 ± 1.3 vs. 38.9 ± 1.6 weeks; mean difference -0.46 weeks, 95 % CI -0.97 to 0.05; p = 0.079). Preterm birth (<37 weeks) was rare in both groups. In the multivariable logistic regression model, CrossFit participation was not associated with increased odds of preterm birth (adjusted OR 0.4, 95 % CI 0.05-3.60, p = 0.42 (Table 5). Mean birthweight (3,195 ± 409 g vs. 3,216 ± 504 g; mean difference 21 g, 95 % CI -141 to 184; p = 0.795) and birthweight percentiles (46.8 ± 24.2 vs. 53.3 ± 26.4; mean difference 6.5, 95 % CI -2.7 to 15.7; p = 0.162) were also comparable. Maternal adverse outcomes occurred in 9.8 % of women who continued exercising versus 13.3 % of controls (p = 0.585), with no significant differences in individual complications.

Appropriately modified CrossFit training maintained at high intensity during pregnancy, was not associated with increased risks of preterm birth, low birth weight, or adverse maternal or neonatal outcomes. These preliminary findings suggest that appropriately modified high-intensity functional training during pregnancy is not associated with observable harm to maternal or neonatal outcomes. While reassuring, these results should be interpreted cautiously and confirmed in larger, prospective studies before definitive safety recommendations can be made.