Implications of idiopathic preterm delivery for previous and subsequent pregnancies

To describe the relationship between pregnancy complications and fetal outcome in first and second pregnancies, focusing on idiopathic and indicated preterm birth of singleton infants in either pregnancy.

Included in the study were 13,967 women in Denmark who gave birth to their first singleton infant in 1982 and a second infant in 1982-1987. Information on pregnancy and birth was obtained by linking the National Medical Birth Register and the National Register of Hospital Discharges, based on personal identification numbers.

The risk of a preterm second birth in women with idiopathic and indicated preterm first birth did not differ significantly (15.2 and 12.8%, respectively). However, women with idiopathic preterm birth in the first pregnancy tended to repeat idiopathic preterm birth twice as often as women with indicated preterm birth repeated indicated preterm birth (11.3 versus 6.4%). Adjustment by logistic regression analysis for other risk factors for preterm birth did not influence the relative risk (6.0 before 32 weeks and 4.8 for 32-36 weeks) of a second preterm birth after a first preterm birth. Women with idiopathic preterm delivery in their first and second pregnancies gave birth to infants with lower birth weight than in previous or subsequent pregnancies. Emergency cesarean delivery in a first term pregnancy was a risk factor for subsequent idiopathic preterm birth.

Idiopathic preterm birth is associated with emergency cesarean delivery at term in previous pregnancies and infants with lower birth weight in previous and subsequent pregnancies.