ABSTRACT
This chapter defines the lower extreme of maternal age as below 20 years of age, since virtually all studies of multiple pregnancy and low maternal age apply this definition. For the upper limit (advanced maternal age), all studies that use the cut-off points of 35 years or 40 years are included. Pregnancies beyond 50 years are excluded, as they are still a rare phenomenon with a probability of 1 in 25 000 births6.
