The contraceptive effect of breast-feeding is the single most important determinant of human population growth rates in traditional societies without access to modern forms of contraception; lactational amenorrhoea is Nature's contraceptive. Even today, breast-feeding still prevents more pregnancies than all modern forms of contraception in many developing countries. Afferent neural inputs from the nipple pass via the spinal cord to the hypothalamus, where they cause a local release of beta endorphin. This acts to depress GnRH secretion, thereby inhibiting pituitary gonadotrophin secretion, ovarian follicular development, ovulation and menstruation. The hypothalamic beta endorphin release also inhibits dopamine production, resulting in increased pituitary prolactin secretion. The higher the suckling frequency, the more beta endorphin that is released and hence the longer the duration of lactational amenorrhoea. Lactational amenorrhoea can be relied up to give over 98% contraceptive protection to breast-feeding women in the first 6 months postpartum, regardless of their nutritional status or the time of first supplement introduction to the baby. This is because the first postpartum menstruation usually precedes the first ovulation during these early months. Once menstruation has resumed, lactation's contraceptive effect can no longer be relied upon, even though the woman continues to breast-feed. In breast-feeding women whose amenorrhoea extends beyond 6 months, there is an increasing tendency for the first ovulation to precede the first menstruation, thereby decreasing the reliability of lactational amenorrhoea as a contraceptive. Nevertheless, many women who continue to breast-feed may still have up to 1-2 years of good contraceptive protection from prolonged lactational amenorrhoea.(ABSTRACT TRUNCATED AT 250 WORDS)
PIP: Traditional nomadic hunter-gatherer societies have long birth intervals of at least 4 years brought about by the contraceptive effect of extended lactation. In some developing countries, lactational infertility continues to prevent more births than any of the modern contraceptives. Afferent neural inputs from nipple stimulation are conveyed through the spinal cord to the hypothalamus. These inputs stimulate the local release of beta-endorphin, which in turn inhibits hypothalamic secretion of gonadotrophin releasing hormone, thereby suppressing secretion of luteinizing hormone from the pituitary, ovarian follicular development, ovulation, and menstruation. Beta-endorphin release also suppresses dopamine secretion, thereby stimulating prolactin secretion. The more infants suckle, the more beta-endorphin circulates, which increases the duration of lactational amenorrhea. The 1st postpartum menstruation almost always occurs before the 1st ovulation during the first 6 months postpartum. In breast-feeding women who still have amenorrhea after 6 months postpartum, 1st ovulation tends to occur before 1st menstruation. Irrespective of maternal nutritional status or the time the infant was first introduced to supplemental foods, lactational amenorrhea protects 98% of breast-feeding women against pregnancy during the first 6 months postpartum. Prolonged lactational amenorrhea may afford women who breast feed 1-2 years good contraceptive protection. In developed and developing countries, women should exclusively breast feed their infants for the first 6 months, and if they have not yet experienced menstruation, they do not need to use contraception. After 6 months, they should supplement lactational amenorrhea with a contraceptive to prevent pregnancy and to achieve at least a 2-year interval between births. The appearance of the first tooth is a signal for supplementing with other food.