Risk factors for preterm birth in an upper middle class Chinese population

Objective: To examine the risk factors associated with preterm birth in an upper middle class Chinese population. Study design: From March 1994 to February 1995, a total of 301 cases (gestational age between 20 and 37 weeks) and 656 controls (gestational age at or greater than 37 weeks) were recruited at Mackay Memorial Hospital, Taipei, Taiwan. Using a case-control study design, logistic regression was used to examine the relative significance of various risk factors associated with preterm birth. Results: Age and educational level were identified as significant risk factors for preterm birth. Multiple pregnancies, fetal congenital anomalies, placenta previa or abruptio placentae, and preeclampsia were found to be strongly associated with preterm birth (crude odds ratios between 6.37 and 25.89); vaginal bleeding during or after the first trimester, prior history of preterm delivery, and two or more previous first trimester abortions were associated with preterm birth to a lesser extent (crude odds ratios between 1.67 and 2.9). The magnitude of the increased risk associated with these variables in preterm birth did not show change to any great extent after age and educational level were adjusted for. Further stratification of these cases into groups with and without premature rupture of the membranes (PROM), showed that a multiple pregnancy was still the leading risk factor of preterm birth in both groups. Carrying an abnormal fetus was the next important risk factor for preterm birth in cases with PROM, but was less important in the group without PROM. However, placenta previa or abruptio placentae and preeclampsia were the next most important factors in the group without PROM. Conclusions: Unfavorable current obstetric conditions and a history of more than two prior abortions and preterm delivery were positively associated with preterm birth.