Maternal prolactin concentrations and lactational behaviour in the early postpartum period in women with lactational amenorrhoea.

OBJECTIVE To compare early postpartum differences in maternal prolactin concentrations and lactational behaviour between women who have short and long periods of lactational amenorrhoea. METHODS Healthy lactating women resuming regular menstruation before 24 weeks [short amenorrhoea (SA) group; n = 15], and at or after 24 weeks [long amenorrhoea (LA) group; n = 15] postpartum were studied from 4 to 12 weeks postpartum. Infant feeding pattern and maternal plasma prolactin concentrations were compared between the two groups using repeated measures ANOVA. RESULTS Breastfeeds/24 h were significantly higher and other feeds/24 h were significantly lower (p < 0.01) at 12 weeks postpartum in the LA group when expressed as a percentage of all feeds. Number of breastfeeds (total/24 h and night) significantly decreased and the number of other feeds significantly increased (p < 0.05 to 0 < 0.001) with time in both groups. Prolactin concentrations (basal, suckling stimulated and increment) were higher in the LA group, but consistent significant differences were observed mainly in the increment (p < 0.05 to p < 0.001). Prolactin concentrations significantly (p < 0.01 to < 0.001) decreased with time postpartum in the SA group, but not in the LA group. CONCLUSIONS Women with longer periods of lactational amenorrhoea maintain higher prolactin concentrations than those with shorter periods of lactational amenorrhoea during the early postpartum period, even when the breastfeeding frequency is reduced. This could be explained by a greater sensitivity of the pituitary lactotrophe to the suckling stimulus in women who have longer periods of lactational amenorrhoea.