The repetition of spontaneous preterm labour.

The likelihood of repetition of preterm birth after spontaneous onset of labour has been studied in 6572 reproductive careers after excluding stillbirths, multiple births, all careers in which any labour had been induced, and all careers in which the gestation length in any pregnancy was not certain. The analysis was controlled not only for pregnancy number, but for the nature of the reproductive outcomes. In most reproductive sequences there was a weak correlation between the gestation in one pregnancy and subsequent ones. The risk of preterm birth was tripled after one previous preterm birth with or without a preceding abortion, and increased six-fold after two previous preterm births. However, the attributable risk was low, and most multiparae with preterm births did not have a previous history.