Objectives: To examine the risk of adverse birth outcome in older primiparous women.
Methods: We identified 14,676 primiparae of 20 years of age or more from 1991 to 1996 using the Birth Registry in the North Jutland County, Denmark. We evaluated the risk of adverse birth outcome in the primiparous women aged 30-34 years and above 35 years using the primiparae aged 20-29 years at time of birth as reference.
Results: The risks of induced labor, perineotomy, stimulating contraction and vacuum extraction were significantly higher (adjusted odds ratio: 1.3 to 1.7) in the primiparae of 35 years or more. The odds ratio for cesarean section delivery was 2.1 (95% confidence interval: 1.7-2.6) and the odds ratio for delivering a low birth weight child among the primiparae of 35 years or more was 2.2 (95% confidence interval: 1.4-3.3) compared with the primiparae of 20-29 years of age. These risk estimates were independent of women's infertility treatment history.
Conclusions: A negative effect of maternal age on birth and neonatal outcome may be seen even after 30 years of age and is partly related to chronic diseases. However, it is impossible to rule out selection bias, but the actual risk must be taken into consideration in antenatal care.