A recent School of Public Health study finds that women who experience a delay of more than one year when trying to get pregnant (subfertility) have an increased risk of spontaneous abortions. In addition, this association between time to conception and rate of spontaneous abortion was significantly higher in younger women than in older women. The study appears in the September issue of The American Journal of Public Healt.

For the purpose of this study, spontaneous abortion is defined as the loss of a recognized pregnancy before week 28 of gestation. "Previous studies have shown a weak association between prolonged waiting time to conception and spontaneous abortions. However, the present study showed the association between subfertility and spontaneous abortion was more significant," said Ronald Gray, a professor in the Department of Population and Family Health Sciences in the School of Public Health.

The study examined 1,572 women ages 15-44 who were employed in both manufacturing and nonmanufacturing jobs at two semiconductor facilities between June of 1989 and July of 1990. Researchers also studied the wives of male employees at those plants. The women reported 2,967 eligible pregnancies with a known waiting time to conception. Permission to review medical records was requested from those who reported having any type of adverse pregnancy outcomes in the past, including spontaneous abortion.

Of the 2,967 pregnancies, 292 (9.8 percent) reported a waiting time of more than one year before conception. Of those 292 pregnancies, the rate of pregnancy loss was 23 percent, whereas women who reported no delay in conception had a 14.3 percent rate of having spontaneous abortion.

The researchers also found women under the age of 30 with no history of fertility problems had a spontaneous abortion rate of 12 percent, but if they had a history of delayed conception the spontaneous abortion rate was 21 percent. Although the total numbers of spontaneous abortions were higher in women over the age of 30, the differential between those who didn't experience a delay in getting pregnant and those who did was smaller, 22 percent and 26.5 percent, respectively.

According to the research team, further studies are needed to confirm and clarify these findings. "It will help us to better manage the care of women who have subfertility and recurrent pregnancy losses," said Gray.

This study was supported in part by grants from IBM and the National Institutes of Child Health and Development.