Abstract

Aims: To determine the effects of increasing maternal age and related maternal and possibly paternal factors.

Methods: A US database of more than 8 million births was analyzed to determine the relationships between maternal age, maternal ethnicity, marital status, maternal smoking and paternal age on twinning rates.

Results: Twinning rates increased proportionally with maternal age. African American women had a higher twinning rate than Caucasian women. Hispanic, Asian and Native American women had comparatively lower rates than Caucasians. After controlling for ethnicity and other maternal factors, increasing maternal age was still related to increased twinning rates. Increased paternal age had a small but significant independent association with an increased rate of twinning.

Conclusions: Both increasing maternal and paternal age are related to increased rates of twinning. This age effect is independent of other factors also associated with twinning.