Breast-feeding rates and related maternal and infants' obstetric factors in Japanese twins

The aims of the present study are to describe the secular trend of breast-feeding rates in Japanese twins in comparison with the general population, and then to clarify the maternal and infants' obstetric factors associated with breast-feeding in twins.

Breast-feeding rates from 0 to 6 full months and related maternal and infant obstetric factors were analyzed using 4,023 Japanese twins, consisting of two different volunteer-based twin samples, age 1-15 years, whose birth year ranged from 1968 to 2003. Data were collected through mailed or hand-delivered questionnaires. Obstetric factors that affect full and partial breast-feeding of twins were confirmed using logistic analyses according to birth order in twin pairs, adjusted by birth year.

The full breast-feeding rates of twins were lower than those of the general population. On the other hand, the combined rates of full and partial breast-feeding were close to those of general population, except for the period 1968-1974. The percentage of concordance pares was around 95% for all months. The most influential factor that negatively correlated with breast-feeding from 0 to 6 months was gestational weeks. Higher maternal age at twin birth and the use of an incubator also prevented breast-feeding in the neonatal period.

The results of the present study for the first time indicated that full breast-feeding of twins has risen recently in Japan, although the rates are still lower than those of the general population. The importance of the gestational weeks for breast-feeding rates was also shown.