Risk factors associated with preterm (<37+0 weeks) and early preterm birth (<32+0 weeks): univariate and multivariate analysis of 106 345 singleton births from the 1994 statewide perinatal survey of Bavaria

Abstract

Objective: The study was conducted to identify medical, obstetrical and social risk factors associated with early preterm births (<32+0 gestational weeks). Study design: The Statewide Perinatal Survey of Bavaria is a collection of perinatal data from all Bavarian maternity units using a uniform numbered questionnaire. Data on 106 345 singleton births from the 1994 Survey were analysed using univariate and multivariate logistic regression analysis. Results: In the multivariate analysis, early preterm birth was associated with premature rupture of the membranes (odds ratio (OR) 1.6, 95% confidence interval (CI) 1.37–1.86), treatment for infertility (OR 1.7, 95% CI 1.19–2.34), previous induced abortion (OR 1.8, 95% CI 1.57–2.13), maternal age >35 years (OR 1.8, 95% CI 1.47–2.16), premature cervical dilatation (OR 2.3, 95% CI 1.86–2.94), a history of stillbirth (OR 3.2, 95% CI 2.13–4.83), a history of preterm birth (OR 3.3, 95% CI 2.45–4.48), maternal age <18 years (OR 3.4, 95% CI 2.03–5.61), malpresentation (OR 3.9, 95% CI 3.10–4.93), preeclampsia (OR 4.0, 95% CI 3.20–4.94), uterine bleeding (OR 5.0, 95% CI 4.08–6.02), preterm labour (OR 7.0, 95% CI 5.94–8.22), and chorioamnionitis (OR 22.3, 95% CI 17.40–28.66). Conclusion: These data identify a subgroup of women at an increased risk for early preterm birth and may benefit from an intensified prenatal care. Risk factors related to the obstetrical history, genital infections, preeclampsia and maternal age are the most relevant for early preterm birth.

Introduction

Preterm birth continues to be the major cause of perinatal mortality and neurological long-term morbidity in the industrialised countries, and its relative importance is still increasing. At least 70% of perinatal mortality is attributable to newborns weighing <2500 g 1, 2, 3, of whom the majority are born preterm.

In Germany, the perinatal mortality rate has dropped under 0.5% in recent years despite the fact that the rate of preterm birth has remained constant at about 6% over the past decade [4]. This reduction in perinatal mortality is mainly due to improvements in intensive care of infants with very low birth weight. However, our attempts to reduce the rate of infants born early preterm (<32+0 weeks) have not been successful in the past [3]. Although it is the morbidity of infants born early preterm that largely influences the rate of permanent intellectual and motoric impairment, only limited information is available about the causes of and associations with early preterm birth [5].

Therefore, we aimed to analyze the risk factors for early preterm birth using the data of the 1994 statewide Perinatal Survey of Bavaria, including 106 345 singleton deliveries. This survey offers a unique opportunity to study the impact of risk factors on the occurrence of term, preterm and early preterm births on a large scale in a mostly uniform population.