History of induced abortion as a risk factor for preterm birth in European countries: results of the EUROPOP survey.

BACKGROUND The objective of this study was to investigate the relationship between history of induced abortion and preterm delivery in various parts of Europe, and according to the main cause of preterm birth. METHODS We used data from a case-control survey, the EUROPOP study; 2938 preterm births and 4781 controls at term from ten European countries were included. Based on national statistics, we distinguished three groups of countries with high, intermediate and low rates of induced abortion. RESULTS Previous induced abortions were significantly associated with preterm delivery and the risk of preterm birth increased with the number of abortions. Odds ratios did not differ significantly between the three groups of countries. The extent of association with previous induced abortion varied according to the cause of preterm delivery. Previous induced abortions significantly increased the risk of preterm delivery after idiopathic preterm labour, preterm premature rupture of membranes and ante-partum haemorrhage, but not preterm delivery after maternal hypertension. The strength of the association increased with decreasing gestational age at birth. CONCLUSIONS Identifying subgroups of preterm births on the basis of the complications involved in delivery increases our understanding of the mechanisms by which previous induced abortion affects subsequent pregnancy outcomes.