Risk factors related to premature rupture of membranes in term pregnant women: a case-control study.

A case-control study of premature rupture of membranes (PROM) of full term pregnant women was undertaken between 1 November 1996 and 30 July 1997 at Rajavithi Hospital to determine the risk factors related to PROM. Two hundred and twenty pregnant women with PROM and 220 pregnant women without PROM were recruited by a simple random sampling. The diagnosis of rupture of membranes was made from history and from positive microscopic ferning and pH tests performed during a speculum examination. The demographic data was not significantly different between the two groups. The risk factors, such as a history of PROM in a previous pregnancy, a history of abortion in a previous pregnancy, and body mass index (BMI) < 20 were significantly different between the PROM group and the control group. However, on using multiple logistic regression analysis, we found that the residual significant risk factors were a history of PROM in a previous pregnancy and BMI < 20.