Increasing maternal age as a determinant of placenta previa. More important than increasing parity?

We studied the relationship of maternal age, parity and placenta previa using information from the Commonwealth of Massachusetts birth certificates for 1987-1988. Multiple logistic regression procedures were used to model data for 600 placenta previa cases and 10,448 randomly selected controls. In analyses that simultaneously controlled for maternal age and parity as well as other risk factors, we found that advanced maternal age was strongly related to placenta previa. Women who were 30 years of age or older were more than twice as likely to have pregnancies complicated by placenta previa as compared with the reference group, women who were 20-29 years of age (adjusted odds ratio, 2.0-2.7). The risk of placenta previa was, to a lesser extent, also associated with increasing parity (adjusted odds ratios, 1.1-1.7).