Introduction

Numerous studies have reported multiple adverse outcomes associated with childbearing at an advanced maternal age. The clinical importance (as opposed to the statistical significance) of the outcomes reported in these studies is variously concluded, with a few suggesting no increased risk. This may be accounted for by subtle differences in study design and data collection. When considering adverse obstetric outcome with respect to maternal age, a cautionary note is therefore advised when reviewing research.

Study designs and pitfalls

Population size is an important consideration. Adverse outcomes, particularly stillbirth, occur infrequently. Only 10—20% of mothers in most populations are aged 35 years or over, 2—4% are 40 years or over and 0.005% are 50 years or over. Large sample sizes are therefore required to determine an effect of age on outcome. Maternal parity also influences obstetric outcome. Primiparity is reported to be most frequent in those aged 20—29 years, with a trough at 40—49 years and then a modest increase at 50 years or over. In the UK, maternal age at the birth of the first child is steadily increasing (Figure 13.1). Any study of a population of older mothers is therefore likely to include an ever-increasing proportion of primiparous women. Great (or grand) multiparity is also more frequently seen among older mothers in some studies: 16% of those aged 40—49 years were grand multiparae compared with 7.0% at 30—39 years and 2.6% at 20—29 years.