Statistics from Altmetric.com
Many people are choosing to put off having children until relatively late in life. In the USA the proportion of first births with mothers in their thirties more than doubled between 1970 and 1990. Similar statistics have been reported from Canada. Is there a biological cost for this social trend? Data from Canada (
) suggest that there might be.
In the province of Alberta there were 42 930 births in 1990 and 37 710 in 1996. At the same time the number of births to mothers aged 35 years or older increased from 3626 (8.4%) to 4798 (12.7%). The number of low birth weight babies increased by 0.5% for mothers aged under 35 and by 11% for older mothers. Preterm delivery increased by 3.5% among younger mothers and by 14% among older mothers. Older mothers accounted for 78% of the increase in low birth weight and 36% of the increase in preterm delivery. Older mothers were not more likely to have small-for-gestational-age babies. During the study period multiple births increased by 15% (twins and 14% (triplets). Older mothers accounted for 15% of the increase in twins. Only 0.36% of births in 1996 resulted from in vitro fertilisation.
Delayed childbearing may lead to an increase in preterm delivery and low birthweight.