Gynecology & Obstetrics
Open Access

Abstract

The End of a Triplet Epidemic and Infant Mortality in Japan, 1999-2008

Yoko Imaizumi and Kazuo Hayakawa

Objective: To estimate triplet rates for like-sexed and unlike-sexed sets, and infant mortality rate (IMR), and also to find risk factors for IMR in triplets.

Study design: These rates were estimated using Japanese Vital Statistics from 1999 to 2008.

Results: Like-sexed and unlike-sexed triplet rates decreased significantly from 1999 to 2008. In 1999, the rate was 2.0-fold higher in unlike-sexed triplets than in like-sexed ones, but the difference decreased to 1.6 fold in 2008. The overall triplet rate was 284 per million deliveries in 1999 and decreased to 163 in 2008. The proportion of neonatal deaths among total infant deaths was 79%. Intensive care of triplets during the neonatal period is very important to decrease IMR. IMR was 36 per 1000 live births in 1999-2000 and decreased to 21 in 2007-2008. The relative risk for younger mothers (<25 years) vs. mothers aged 35-39 years was 2.0-fold and that of mothers aged ≥ 40 years vs. age 35-39 years was 3.0-fold. IMR decreased as gestational age increased, and the lowest IMR was 4.9 for ≥ 34 weeks. IMR decreased as birth weight (BW) increased and the lowest IMR was 4.5 for BW ≥ 1500 g.

Conclusion: Triplet rates for unlike-sexed sets decreased by 50% during the period. The changes in the rate of triplets may signal the end of a triplet epidemic. IMR for extremely low BW infants was independent of maternal age but not of gestational age. The lowest IMR was for second-order triplets.