Until the 2nd and 3rd decades of this century, breastfeeding was essential for infant survival. In that period, spacing of children was generally about 2 years. Later, improved modified cow's milk preparations became commercially available and were well tolerated by most infants. As a result, near cessation of ecological breastfeeding occurred toward the middle of the century. The decline in ecological breastfeeding was associated with early postpartum ovulation and shortened child-spacing of about 1 year. The endocrinology of breastfeeding is now known in considerable detail. Prolactin is secreted promptly in response to nipple stimulation and is a reliable marker of the endocrine alterations occurring postpartum. Success of lactation in suppression of ovulation was found to occur when infants sucked frequently and when only small amounts of selected foods were introduced gradually after the infants were about 6 months of age.
PIP: Ecological breastfeeding can have a favorable effect on child spacing because of the natural suppression of ovulation associated with lactation, but breastfeeding alone cannot be depended upon for birth control. Ecological breastfeeding consists of feeding only human milk for about 6 months, suckling on demand day and night, no pacifiers, gradual introduction of small amounts of selected foods at about 6 months, and continuation of nursing as the primary food for about 1 year or longer. The rapid decline in ecological breastfeeding that occurred over the 1930-60 period resulted in early postpartum ovulation and in shortened child-spacing of about 1 year. Since 1950 there has been evidence by serial postpartum basal temperature recordings and by histological examination of endometrial biopsies that breastfeeding suppresses ovulation. Nursing women maintain a higher prolactin level and lower gonadal hormone or gonadotropin level postpartum than do non-nursing women. Fertility can return prior to the renewal of menstruation, but women who slowly reduce the frequency of breastfeeds by gradually introducing only small servings of other foods over a period of months are likely to have 1 or 2 infertile menstrual cycles. In general, nonbreastfeeding mothers have postpartum amenorrhea for only a few weeks, but truly lactating mothers experience amenorrhea for about 9-18 months, depending primarily on how often the infant suckles.