J
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.
