Aims: To determine trimester-specific risk factors for small-for-gestational-age (SGA) infants.
Methods: A population-based prospective cohort study was conducted in Sri Lanka from May 2001 to April 2002. Pregnant women were recruited on or before 16 weeks of gestation and followed up until delivery. The sample size was 690. Trimester-specific exposure status and potential confounding factors were gathered on average at 12th, 28th and 36th weeks of gestation. SGA was assessed using customised birth centile charts. Multiple logistic regression was applied, and the results were expressed as odds ratios (OR) and 95% confidence intervals (95%CI).
Results: The risk factors for SGA less than 5th centile were shift work and exposure to physical and chemical hazards during 2nd and 3rd trimesters (OR 4.20, 95%CI 1.10–16.0), sleeping for less than or equal to 8 h during 2nd or 3rd or both trimesters (OR 2.23, 95%CI 1.08–4.59), walking for less than or equal to 2.5 h per day (OR 2.66, 95%CI 1.12–6.31) and alcohol consumption during the 3rd trimester (OR 14.5, 95%CI 2.23–94.7). Poor weekly gestational weight gain was significantly associated with both SGA < 10th and < 5th centiles. None of the other factors became significant for SGA < 10th centile.
Conclusions: Risk factors for SGA less than 5th centile were sleep deprivation and shift work and exposure to physical and chemical hazards during 2nd and 3rd trimesters, less walking hours and alcohol consumption during 3rd trimester. Poor weekly gestational weight gain may be considered as a predictor of delivering an SGA infant.