Multiple births: trends and patterns in Canada, 1974-1990.

This paper examines Canadian trends and patterns in multiple births in relation to total confinements, singleton births, maternal age, parity, gestational age and birth weight using vital statistics from 1974 to 1990. Multiple-birth rates in Canada increased from 912.8 to 1,058.9 per 100,000 confinements between 1974 and 1990. The increase is especially noticeable for women over 30. The rate of triplet and higher-order births increased from 8.3 to 21.7 per 100,000 confinements between 1974 and 1990. The proportion of multiple-birth babies that were pre-term (< 37 weeks gestation period) increased from 32.8% in 1974 to 45.8% in 1990. Factors associated with the increase in multiple births may include the use of assisted pregnancy techniques, and the fact that women aged 30 and older, who are at higher risk of a multiple birth, and who postponed their child bearing, have increased their fertility. The sharp increase in multiple-birth rates has implications for maternal and child health and health care costs.