Very and moderate preterm births:: are the risk factors different?

Objective To describe the risk factors for very preterm births and to compare the strengths of the associations between these risk factors and very and moderate preterm births. Design A case-control study. Setting Fifteen European countries. Methods Between 1994 and 1997, 1675 very preterm births, 3652 moderate preterm births and an unmatched control group of 7965 births at term were included. Odds ratios for very and moderate preterm births (related to socioeconomic status, behavioural factors, maternal age, body mass index and obstetric history) were estimated and compared using polytomous logistic regression. Results Underprivileged social situation, older maternal age and adverse previous pregnancy outcomes were significantly related to very and moderate preterm births. However, these factors were more strongly associated with very preterm births than with moderate preterm births, for both spontaneous and induced deliveries. Smoking during pregnancy, young maternal age and low body mass index were significantly related to very and moderate spontaneous preterm births, but no significant difference in odds ratios was observed between the two outcomes. Conclusion These results suggest that risk factors for very and moderate preterm births are similar, but the strength of the associations differ, especially for social factors and obstetric history.