There are a number of limitations of this study. Firstly, since the study design was retrospective, some recall bias in mothers relating to the time to first breastfeed may have affected our results. Secondly, as the participants took part in a physical examination of their four month old infants, some selection bias or confounding factors may have occurred. Among 391 mothers who were mailed to a questionnaire, some mothers did not participate in a physical examination of their infants because of their baby's or their own health problem. Therefore, the study participants and their baby could be healthier than those who did not participate in the present study. However, since the response was high (83%), the extent of selection bias may be small. Another possible source of bias was that mothers who put the baby to their breast in the first two hours were more motivated to breastfeed than the other mothers. Their infant feeding intention could lead to continuation of fully breastfeeding their infants up to four months. As it is not feasible to conduct a randomized controlled trial on this topic, we thought that the information collected in the study was worth analysing.
The present study revealed four findings associated with initiation and maintenance of breastfeeding in Japanese women. Firstly, 36% of 318 mothers breastfed within 30 minutes, and 57% breastfed within 120 minutes. If more women could be encouraged to start breastfeeding early we may see a higher rate of full breastfeeding. Secondly, severe bleeding during delivery, premature delivery, and caesarean section were obstacles for early breastfeeding. If it is possible to attempt early breastfeeding during these conditions, for example, by delaying routine neonatal procedures and keeping mother and baby in close proximity , we can further promote early breastfeeding. Thirdly, mothers who initiated breastfeeding within 120 minutes maintained full breastfeeding during their stay in the clinic/hospital, at one month and at four months after birth. The rate of decline in breastfeeding was significantly slower for infants who were first suckled early than for those who were first suckled later [11, 12]. Fourthly, the proportion of full breastfeeding mothers did not differ between first breastfeeding within 30 minutes and first breastfeeding within 31 to 120 minutes. Righard reported that infants require 49 minutes on average in order to initiate breastfeeding through their own efforts and sucked for about 20 minutes . Widstrom reported that it takes 55 minutes for infants to start suckling after birth . On the other hand, catecholamine is secreted rapidly within 120 minutes by newborn infants, this period is called "the newborn infant awaking term" . A previous study revealed that first breastfeeding within 120 minutes was significantly associated with skin-to-skin contact, and extended the duration of subsequent breastfeeding . We should not hurry to commence breastfeeding immediately after delivery, as the first breastfeed within 120 minutes was associated with maintenance of breastfeeding up to four months. It might be suggested that the recommended timing of the first breastfeed should be extended to within 120 minutes.
In the present study, the proportion of mothers who continued full breastfeeding at 4 months was higher in female infants than in male infants. A previous study  in Latin American countries (Brazil, Honduras and Mexico) reported that male infant was significantly associated with cessation of exclusive breastfeeding. Another study  in Greece analyzed factors affecting intention to breastfeed, and found that male gender was associated with negative attitude of breastfeeding. It is possible that mothers may think that male infants need more nutrition than female infants, and they may add infant formula earlier. To the contrary, a study in China  reported that girls were breastfed for a significantly shorter period than boys because of preference for sons. Another possible reason for the lower proportion of full breastfeeding in male infants was that male infants might have more medical problems and more difficulties with breastfeeding. A study  suggested that infants with ankyloglossia, which is more common in male than in female, had more difficulties with breastfeeding, defined as nipple pain lasting longer than 6 weeks and/or difficulty of the baby latching onto the breast. The higher frequency of medical problems in male infants might have affected the lower proportion of full breastfeeding at four months.
The mother who has early contact with her baby and initiates breastfeeding after delivery might have enhanced maternal behaviour compared with the mother who does not . Early contact with the baby immediately after birth will promotes a closer relationship between a mother and her baby. Moreover, the early initiation of breastfeeding gives the mother a strong sense of satisfaction . Maternal satisfaction with first breastfeeding was associated with early initiation of breastfeeding within 120 minutes in our study (data not shown). Moreover, some mothers responded to our questionnaire, and described their feelings about breastfeeding as "I felt motherly love", "I increased the pleasure of childbirth" and "I felt calm". Early breastfeeding helped to calm mothers and make them feel relaxed. Early breastfeeding not only increased the proportion of mothers maintaining full breastfeeding, but produced positive mental effects in the mothers.