Trends in twin births in New South Wales, Australia, 1990-1999.

OBJECTIVE: To examine trends in gestational age and the mode of delivery of twins.

METHOD: All twin births in New South Wales, Australia from 1990 through 1999 were analyzed.

RESULTS: Twin births increased from 1922 (2.2%) in 1990 to 2522 (2.9%) in 1999. Twins born preterm (<37 weeks) increased from 40.8 to 48.8%. The increase in preterm twin births was associated with increases in induction of labor and cesareans before labor at 32-36 weeks. The rate of fetal deaths decreased by 49% and Apgar scores <4 at 5 min by 28%.

CONCLUSIONS: A greater than expected increase in preterm twins was largely explained by an increase in elective deliveries at 35-36 weeks' gestation. Increasing maternal age does not appear to have contributed to the increase in preterm twin births. Lower rates of fetal death and low Apgar scores were achieved seemingly at the price of delivering more infants before term.