The fertility regulating effect of breastfeeding has been known for underestimated. This has been due mostly to the lack of knowledge of the events associated with breastfeeding that determine its contraceptive effect. It is now known that breastfeeding per se is not a particularly effective or reliable means of contraception. On the other hand, the period of amenorrhea associated with breastfeeding, commonly referred to as lactional amenorrhea, provides an important degree of contraceptive effect.
Physiology of Contraceptive Effect of Breast Feeding
„h Endocrine Responses to Breastfeeding
The physiological response to suckling at the breast is ...view middle of the document...
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 on the pattern of suckling unless there exists refractoriness or some other form of non-linearity in the mechanism of prolactin synthesis and release. A possible theoretical base for understanding this problem has been given by the experimental work or Charles Grosvenor and his associates at the university of Tennessee. Grosvenor's group found that a metabolite of TRH, cylco-his-pro, inhibits the transformation of prolactin in the pituitary from a pre-releasable to a releasable form. They theorise that TRH released by the hypothalamus in response to the suckling inhibits the release of dopamine from the TIDA (tubero-infundibular dopaminergic) neurones of the hypothalamus, thus removing the chronic inhibition of the transformation of prolactin from its pre-releasable to its releasable form. However, TRH is quickly metabolised, yielding cyclo-his-pro that blocks further transformation. After an interval has elapsed between suckling bouts, the refractory state abates. A new suckling stimulus then is capable of triggering another prolactin release and an...