Sedentary behaviour and physical activity across pregnancy and birth outcomes

Shorter gestation or smaller birth size are indicators of a suboptimal fetal environment and negatively impact short- and long-term offspring health. Understanding how modifiable maternal behaviours, such as moderate-to-vigorous intensity physical activity (MVPA) or sedentary behaviour (SED), improve fetal outcomes could inform strategies to improve health across the lifespan.

The objective of this study was to examine the association of MVPA and SED across pregnancy trimesters on gestational age at delivery and newborn anthropometrics.

The MoM Health Study measured SED (thigh-mounted activPAL3 micro) and MVPA (waist-worn Actigraph GTX3) in each trimester of pregnancy. Birth outcomes (gestational age at delivery, birthweight, birth length, and head circumference) were abstracted from medical records and used to calculate ponderal index (grams*100/cm³ ) and size-for-gestational age percentiles. Associations of group-based trajectories and trimester-specific SED and MVPA with birth outcomes were analysed using regression models.

Low, medium, and high trajectory groups were generated SED and MVPA in 103 and 99 pregnant women, respectively. High vs low SED trajectory was associated with earlier gestational age at delivery (β -1.03 weeks, 95% CI -2.01, -0.06), larger head circumference (β 0.83 cm, 95% CI 0.24, 1.63), longer birth length (β 1.37 cm, 95% CI 0.09, 2.64), and lower ponderal index (β -0.24 g*100/cm³ , 95% CI -0.42, -0.06), after adjustment for demographics, pre-pregnancy BMI, and (for newborn anthropometric outcomes) gestational age. The association of high SED with lower ponderal index was the most robust across progressively adjusted models (β -0.25 g*100/cm³ , 95% CI -0.44, -0.07). SED trajectory was not associated with birthweight or size-for-gestational age. High vs low MVPA trajectory was only associated with smaller head circumference (β -0.86 cm, 95% CI -1.70, -0.02).

Higher SED during pregnancy may result in shorter gestation and inhibited fetal growth. Further research evaluating the effect of reducing SED during pregnancy on birth outcomes is warranted.