Shorter sleep duration in early pregnancy is associated with birth length: a prospective cohort study in Wuhan, China.

OBJECTIVES: To examine the association between sleep duration in early pregnancy and fetal growth in a prospective cohort study of 3567 Chinese women.

METHODS: Pregnant women at 8-16 weeks of gestation were interviewed using a semi-quantitative questionnaire to assess sleep duration. Birth weight and birth length were measured by a midwife in the delivery room at birth; low birth weight (LBW) was defined as birth weight <2500 g and small for gestational age (SGA) was defined as <10th customized centile.

RESULTS: The average age of participants was 28.21 ± 3.38 years old. The mean sleep duration was 8.39 ± 1.13 h/day. A total of 1290 women sleeping ≥9 h/day, 1563 sleeping 8 to <9 h/day, 550 sleeping 7 to <8 h/day, and 164 sleeping <7 h/day. Compared to the sleeping 8 to <9 h/day group, birth length and birth weight of the sleeping <7 h/day group decreased by 2.42 mm (95% CI: -4.27, -0.58, p = 0.010) and 42.70 g (95% CI: -103.02, 17.62, p = 0.165), respectively; and risk of LBW and SGA of the sleeping <7 h/day group increased by 83% (95% CI: 0.59, 5.73, p = 0.297) and 56% (95% CI: 0.84, 2.92, p = 0.159), respectively; birth length of the sleeping <7 h/day group was decreased more in male babies, and among mothers without a midday napping habit or with a history of abortion (all p for interaction <0.05).

CONCLUSIONS: Shorter sleep duration in early pregnancy was associated with birth length. Our findings indicate that midday napping may be a protective factor for birth length among pregnant women with shorter sleep duration.