Factors associated with spontaneous pre-term birth.

Factors associated with spontaneous pre-term birth in 283 singleton pregnancies were compared with those present in a total population of 16 994 women at risk studied in the First British Perinatal Mortality Survey. It was shown that the risk of spontaneous pre-term birth was related to low maternal age, low maternal weight, maternal smoking, low social class, illegitimacy, threatened abortion, and a previous history of antepartum haemorrhage, perinatal loss, or low birth weight livebirths.