[A case-control study on small-for-gestational-age in relation to obstetrical risk factors]

Previous studies suggested that a number of obstetrical factors were associated with small-for-gestational-age (SGA) infant. However, it remained uncertain which obstetrical factors might increase the risk of SGA due to limitations of small sample size and poor study designs in the previous studies in China. We assessed the association of a few maternal factors, such as pregnancy-induced hypertension (PIH), oligohydramnios, infectious diseases of reproductive system, abnormal conditions of placenta or umbilical cord, previous adverse pregnancy outcomes, hysteromyoma and maternal education level, and the risk of SGA.

We examined the association in a case-control study, in which the SGA group included all of 834 (443 males and 391 females) singleton alive SGA deliveries in our hospital during January 2000 to October 2004. 2502 (1329 males and 1173 females) appropriate-for-gestational-age (AGA) infants (1:3, SGA/AGA) matched by gender- and gestational-age-stratified frequencies of SGA were randomly selected for controls from infants with sex-specific birthweight for gestational age ranged between 10th-90th percentiles. Odds ratios (95% confidence interval, 95% CI) of these factors for SGA were calculated in univariate and multivariate analyses. The maternal risk factors were diagnosed by the relevant criteria used in China. SGA was defined as sex-specific birthweight for gestational age that was less than 10th percentile cut-off of fetal growth reference of singleton alive infants delivered in our hospital during that period.

Results from univariate analysis showed that PIH, oligohydramnios, history of adverse pregnancy outcome, poor maternal education and viral hepatitis were significantly associated with SGA. The odds ratios (95% CI) of these five factors for SGA were 3.95(2.79-5.60), 2.94(2.27-3.80), 7.01(3.87-12.70), 3.62(2.92-4.49) and 0.52(0.32-0.87), respectively. In the multivariate logistic analysis, a similar result was shown. The ratios of maternal PIH, oligohydramnios, history of adverse pregnancy outcome and viral hepatitis in the SGA group were 4.00(2.81-5.71), 2.95 (2.27-3.83), 5.95 (3.05-10.64), 0.50(0.30-0.84) folds of those in the AGA group; the ratio of maternal low formal education (< or = 9 years) in the SGA group was 3.46(2.75-4.24) times of the AGA group.

PIH, oligohydramnios, poor maternal education and a history of adverse pregnancy outcome were significantly associated with an increased risk of SGA while viral hepatitis might be associated with a decreased risk of SGA.