Paediatr Perinat Epidemiol. 2001 Oct;15(4):346-51.
Infant mortality rates in single, twin and triplet births, and influencing
factors in Japan, 1995-98.
Imaizumi Y.
Faculty of Health Science, Hyogo University, Hiraoka-cho, Kakogawa City,
Hyogo Prefecture 675-0101, Japan. imaizumi@humans-kc.hyogo-dai.ac.jp
The infant mortality rate (IMR) was analysed among single, twin and triplet
births during the period from 1995 to 1998 using Japanese Vital Statistics.
This study also investigated the effects of order of multiple births and of
birthweight on the IMR. Proportions of neonatal deaths among total infant
deaths were about 1/2 for singletons and 3/4 for both twins and triplets.
Thus, to reduce the IMR, intensive care of multiple births is likely to be
very important during the first month of life. The IMR was higher in males
than females for both singletons and twins, but not in triplets. Relative
risks of the IMR in multiples relative to singletons were 5-fold in twins
and 12-fold in triplets. The IMR was higher in the second-born (18 per 1000
live births) than the first-born (16) twin and higher in the third-born (51)
than the first-born (31) and the second-born (34) triplet. The higher risk
in the second-born than the first-born twin may be related to delivery
complications. The IMR decreased rapidly as birthweight increased in
singletons, twins, and triplets. IMRs for < or =1500 g were 2.4 per 1000
live births in singletons, 5.9 in twins and 6.1 in triplets. The
corresponding proportions of infant deaths were 75%, 33% and 10%
respectively. The higher relative risks of multiple births are almost
entirely the result of the lower birthweight distribution among twins and
triplets. To reduce the IMR, birthweight is an important factor in twins,
triplets and singletons. The overall early neonatal death rate decreased as
gestational age rose in singletons, twins and triplets. For birthweights
<1000 g, higher IMRs were related to gestational ages of <28 weeks.
