BACKGROUND: Preterm birth and small for gestational age (SGA) are strong indicators of neonatal adverse outcomes. With the growing importance of preterm SGA infants, we aim to evaluate the prevalence and risk factors for preterm SGA in China.

METHOD: We analyzed the data of parents and infants from a population-based cohort research of the free National Pre-pregnancy Checkups Project (NPCP) in rural China. Only singleton live births that occurred between 24 weeks +0 days and 36 weeks +6 days of pregnancy were included in this study. SGA was defined as birth weight less than the 10th percentile of the reference birth-weight-for-gestational-age population. A multiple logistic regression model was built using the statistically significant variables from the 371 variables in the questionnaire.

RESULTS: A total of 11,474 singleton, preterm, live-birth infants were included. Of the total infants, 317 (2.77%) were preterm SGA infants. A higher risk of preterm SGA infants was observed among mothers who were on oral contraceptives (OR: 8.162, 95% CI: 1.622-41.072), mothers who had syphilis (OR: 12.800, 95% CI: 1.250-131.041), and mothers with a high eosinophil percentage (OR: 13.292, 95% CI: 1.282-135.796). Maternal intake of folic acid at least 3 months before pregnancy (OR: 0.284, 95% CI:0.124-0.654) and paternal intake of egg and meat (OR: 0.097,95% CI:0.030-0.315) were protective factors. Compared with North China, the incidence of preterm SGA infants was higher in South China.

CONCLUSION: Preterm SGA infants were associated with both maternal and paternal factors.