prospective, longitudinal study of thirty-four breastfeeding mothers. Their data suggest that prolactin concentration might provide a sensitive index of the return of menstruation and fertility during lactation. According to their model, serum prolactin concentration at any week after delivery is dependent on:-1. Some fixed early perinatal rate of decline in concentration. 2. The number of weeks that unsupplemented breastfeeding continued. 3. The number of weeks of supplemented breastfeeding. 4. The number of weeks since the onset of weaning. The model assumes that ovulatory cycles would ensue once the average serum prolactin concentration has fallen to a threshold below which ovulation suppression no longer can be maintained. The hypothesis that the pattern of suckling stimulation determines the extent of the fertility suppressing effect was suggested in a review by McNeilly et al. Wood et al. developed a similar hypothesis in relation to their study of the Gainj people of New Guinea. The authors suggested that a pre-nursing concentration of prolactin will be re-established in about three hours unless another nursing episode intervenes. They base their reasoning on the observation thta serum prolactin concentration peaks within thirty minutes of initiation of nursing and the understanding that prolactin is removed from circulation with a half-life of about thirty minutes. According to their observations, a typical pattern for a Gainji infant would be three minutes suckling every half-hour, whereas an American infant might be in a schedule of thirty minutes every five hours, on the average. Wood et al. predict that the pattern of short, frequent bouts would produce higher average and basal prolactin concentrations and thus prove to be more effective in suppressing fertility than longer duration , infrequent bouts of nursing. It is difficult to see hoe the basal and average prolactin concentrations could be dependent...
