Reference birth-length range for multiple-birth neonates in Japan


  • Supported by a Grant-in-Aid for Scientific Research (KAKENHI, Grant No. 13670407) from The Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.

Reprint request to: Dr Noriko Kato, Department of Education Training Technology and Development, National Institute of Public Health, 2-3-6 Minami, Wako-shi, Saitama 351–0197 Japan. Email:


Aim: To clarify the birth length of twins according to gestational age.

Methods: We studied a total of 51 910 live-birth–live-birth pairs of twins, 4561 triplet live births and 256 quadruplet live births, using data obtained from corresponding birth certificates. The birth length of twins was analyzed according to gestational age.

Results: Compared to singleton neonates, the median birth length of twins was approximately 0.5 cm smaller after the gestational age of 34 weeks, increasing to approximately 2.0 cm at 42 weeks of gestation. The median birth length according to gestational age was found to be the greatest in twins, lower in triplets and the lowest in quadruplets, in which the difference was <2.0 cm.

Conclusion: The birth length of twins was smaller than that of singletons, but the difference was smaller than the difference in birthweight between twins and singletons.