Perinatal mortality in triplet births in Japan: time trends and factors influencing mortality.

Perinatal mortality rates (PMRs) in triplets were analyzed using Japanese Vital Statistics during the period of 1980-1998. The total number of perinatal deaths in triplets was 1051. The PMR significantly decreased from 214 per 1000 births in 1980 to 39 in 1998, a reduction of 82%. PMRs in triplets were 11.1-fold higher in 1980 and 6.9-fold higher in 1998 than in singletons, indicating that PMRs improved more in triplets than in singletons during the last two decades in Japan. The PMR was the highest in the third-born, followed by the second- and the first-born triplets in each period. As for maternal age, the PMR was 1.5-3.7 times higher in the < 25 years of age group than the other age groups. Additionally, the PMR was the lowest for birthweight (BW) >or= 2000 g during the entire period. In addition, the PMR decreased with gestational age (GA) of up to 38-39 weeks and increased thereafter. The effects of BW on the PMR were stronger than the effects of GA. The proportion of perinatal deaths in triplets with extremely low BW (< 1000 g) was 74% in 1980-1989 and increased to 82% in 1990-1998. The declining PMR was unlikely to be due to the improvement in BW in triplets. It is likely that it was related to the improved medical management of triplets during the perinatal period and the first week of life. Information obtained in the present study may be useful in counseling pregnant woman about triplet births.