Fetal loss, gravidity, and pregnancy order.

An investigation of the reproductive history of 3068 women doctors showed that the risk of fetal loss at a given pregnancy order varied with their gravidity--that is, the total number of pregnancies that has occurred before the survey. Fetal loss rates in even the first pregnancy varied with eventual gravidity in a J-shaped manner. They fell from 12.4% in women with only one pregnancy at the time of the study, to 5.7% in women with two, and then increased steadily to 36.8% in those with six pregnancies. This variation in risk remained when allowance was made for the incomplete nature of some of the reproductive histories. When gravidity was held constant, fetal loss rates decreased with each successive pregnancy. This finding conflicts with previous suggestions that the risk of fetal loss increase with pregnancy order and age.