In adult life the human breast, unlike that of other species, is sufficiently developed to allow milk secretion to occur after only a brief period of hormonal stimulation. During pregnancy the ducts and secretory alveoli develop under the influence of both oestrogen and progesterone. Growth hormone and placental lactogen are not required; the role of prolactin in mammogenesis remains questionable. Lactogenesis, the onset of milk secretion, is inhibited during pregnancy despite high levels of prolactin, by a direct inhibitory action of steroids on the breast. The clearance of placental steroids after delivery removes this inhibition and milk secretion is initiated.

Inhibition of prolactin secretion prevents milk secretion, suggesting that prolactin is the essential hormone for lactation in man. Prolactin release occurs in response to suckling and the amount released depends on the strength and duration of the suckling process. No release of prolactin occurs in response to stimuli other than stimulation of the nipple.

Removal of milk from the mammary gland is effected by the milk-ejection reflex (MER) involving the release of oxytocin in response to suckling. Unlike prolactin, oxytocin may be released in response to stimuli associated with breast-feeding, e.g. the cry of the infant. The MER may be inhibited by psychological and physical stress, either by inhibiting oxytocin release or by preventing its action upon the breast contractile elements. The susceptibility of the MER to disturbance requires consideration when encouraging the establishment of breast-feeding.

Breast-feeding is geared directly to the needs of the infant, since not only does the suckling infant obtain its present meal by inducing oxytocin release, but also by stimulating prolactin release it orders the next (Tindal, 1972).

An ever-changing secretory pattern of pituitary gonadotrophins and prolactin has been observed in puerperally lactating women. Studies in our laboratory suggest such changes are under neurogenic control via the breast. This in turn alters hypothalamic function. Endocrine profiles in lactating women obtained over 10 hours indicate that prolactin secretion and, to a lesser extent, LH secretion, are directly related to the duration and intensity of the suckling stimulus. Thus, lactation performance governs pituitary-ovarian function. Other investigators have shown that alterations in hypothalamic catecholamine turnover represents the interface between nipple stimulation and subsequent pituitary hormone secretion. Although further work is necessary to elucidate the exact neuroendocrine pathways involved, full lactation will effectively delay the restoration of cyclic gonadotrophin secretion and ovulation.

Many mothers in low-income countries, particularly in rural areas, nurse their children for 1–2 years on the average. The main purpose of this practice is, of course, to provide the newborn child with the nutrition necessary for its survival. Prolonged breast-feeding, however, also has a birth-spacing effect and postpones the next pregnancy by inhibiting ovulation and by delaying resumption of the menstrual cycle. Suckling of the infant is important for this suppression of the menstrual cycle because it leads to the release of prolactin, which not only plays an important role in milk production but also inhibits the release of gonadotrophins which initiate resumption of the menstrual cycle. For further details about these endocrinological aspects of lactation see, for example, Rolland et al. (1975); Thomson, Hytten & Black (1975) and Buchanan (1975).

Breast-feeding in the human and higher primates unlike the case of most other mammals, is learned rather than instinctive; over a long time it has been shown to be highly labile. Its success appears to depend not only upon the capacity of the mother to lactate, i.e. to produce milk, or on the child's ability to suckle, but perhaps more significantly, on the mother's desire to breast-feed, on the availability of sufficient reference models upon which she can base her own performance and draw upon for psycho-social support during lactation. In modern settings breast-feeding is likely to involve the mother in complex and new role situations, and to become increasingly vulnerable to the social characteristics of the environment in which she operates.

The process of urbanization in the Third World has vastly outstripped the equivalent change in industrialized countries, and also far exceeds the population growth. This urbanization has been associated with the spread of artificial feeding and associated short birth intervals. Although relatively few studies have been undertaken on the effect of length of birth interval, we have good evidence that it is associated with poorer growth, a less satisfactory intellectual development, and a higher mortality. Child health programmes have, up to the present, been only marginally involved in the question of birth interval, although as mentioned this has a considerable effect on the health of the child. In overcoming malnutrition, simple weight charts are now widely accepted as a useful tool by which the adequate growth of the child can be monitored, and in this way malnutrition prevented. These same weight charts can be a useful means of identifying in any community the month in which a woman has a 5% chance of conceiving again. The charts can also be used as a means of recording the dialogue between the health worker and the parents on the most appropriate time interval to separate their children. However, to achieve this the developing countries will need a vast increase in the health personnel they have available. Experience now in a number of countries suggests that the part-time health worker may be particularly appropriate for providing such services.

It is generally acknowledged that the popularity of breast-feeding, expressed in terms of the frequency with which it is taken up, and the length of time it is continued, is declining, and that, especially among populations of the Third World, the implications of this decline for infant health are likely to be serious and far reaching.

One of the major goals of health programmes in the developing world is to improve maternal and child health. Two important steps towards achieving this goal are the promotion of birth spacing and the promotion of breast-feeding. Since birth spacing requires some type of fertility control measures, modern contraceptive programmes are becoming an integral part of maternal and child health programmes. The next logical question would then appear to be, ‘What are the appropriate contraceptives, particularly among the modern methods, for use during lactation ?’

Although steroid contraceptives have been in widespread use for many years, there still appears to be considerable uncertainty in the minds of many clinicians and family planning programme decision-makers regarding their prescription to nursing mothers. This uncertainty appears to be reflected in replies to a questionnaire sent by the Human Reproduction unit of WHO to scientists in its network of Collaborating Centres for Clinical Research in Human Reproduction regarding the current status of the use of steroid contraceptives by nursing mothers in different national settings. Although the information was, of necessity, in some cases imprecise, the following impressions were gained about eighteen countries: (Australia, Canada, Chile, Egypt, Holland, Hungary, India, Mexico, Nigeria, Philippines, Singapore, Sri Lanka, Sweden, Thailand, Turkey, United Kingdom, USA, Zambia).

One hundred and thirty six lactating women were studied, 42 controls and 94 taking oral contraceptives. Combination pills of oestrogen and progestogen (Primovlar and Minovlar) and a low dose progestogen pill (Norgestrel) were used. The selection of a particular formulation was based on the endocrine profile of an individual; this reduced drop-outs due to side effects.

The change in the quantity of milk was assessed by test-feeding followed by manual expression. Milk was also analysed quantitatively. Significant reduction in the milk yield was found with the Primovlar and Minovlar groups but no change was observed with Norgestrel. No change in the quality of milk was found for any of the three groups.

The contraceptive method used during lactation should be chosen on the basis of (a) effectiveness in preventing pregnancy and (b) its effect on lactation. Combined hormonal contraceptives affect lactation adversely due to the oestrogen component. Progestogen-only contraceptives may increase the quantity and quality of milk yield during lactation. In the present study the effects of four progestational drugs used immediately after delivery were investigated. No adverse effect on initiation of lactation was found. The side effects of the drugs are reported. No pregnancies were reported during the period of the study.

Side effects of steroid contraception during lactation are discussed and followed by a review of the relevant literature. It appears that oestrogen has an inhibiting effect on lactation performance, but progestogen alone does not. Most of the undesirable systemic side effects of oral contraceptives on the mother are connected with the relative excess or deficiency of the oestrogen and/or the progestogen component. It is likely that a low oestrogen content preparation causes no dangerous side effects. There are few data about the appearance of contraceptive steroids in breast milk. Probably only a small proportion of the steroids are excreted into the milk. Any adverse effects, on the infant, such as slow weight gain, neonatal breast hypertrophy and breast milk jaundice, are dependent on the two preceding factors. It is doubtful whether the small amount of contraceptive steroids contained in modern pills exert any influence on the fetus. Although further examinations are necessary, the low dosage of progestogen and oestrogen combined contraceptives given at fully established lactation under close control seems to be advantageous to both mothers and their infants.

The realization that steroidal contraceptives administered immediately after delivery to lactating women may be excreted into milk, and adversely affect the neonate, is a cause for concern. Most investigations on hormonal contraceptives have dealt with the efficacy of ovulation suppression, and systemic side effects, but little is known about the appearance of steroids or their metabolites in milk. Apart from the immediate side effects on the neonate, unforeseen long-term consequences require special consideration. Until research provides us with more information, women should use breast-feeding and IUDs instead of steroidal contraceptives during the first trimester post-partum.

I have not encountered any evidence, anecdotal or otherwise, that lactation is influenced by male methods of contraception including coitus interruptus, or by female barrier or chemical (other than hormonal) methods.

The use of intrauterine contraceptive devices (IUDs) has been claimed to enhance lactation. In Chile, Gomez-Rogers et al. (1967) studied 81 women fitted with IUDs at an average of 50 days post-partum, in whom the lactation half-life (time when 50% had stopped nursing) was 7 months 21 days. In 150 controls, the lactation half-life was 4 months 21 days, the difference being statistically significant.

We have assumed from the temperate world that the cow is essential; we need to question this assumption. The answers will vary considerably from country to country. I suggest that there are two sorts of country: first, countries such as Bangladesh and Nigeria, where no possibility of a milk industry exists. Therefore, if milk is used it has to be imported.

It is a presumption for us in the West to say so, but I suggest that the sensible action is to reduce progressively milk imports and to look at substitution of other materials. A certain amount of work has been done on soya milk; however this may not be suitable as it may be difficult to produce at village level. There are many other possibilities; for example, if a child with a chronic diarrhoeal problem is admitted to a hospital where I work it is fed on a mixture of chicken, glucose and oil. This sort of mixture could be made up in a village. We need to look at such possible alternatives for infant feeding.

We have heard a lot about the promotion of sales of baby food, but we have never analysed the population's readiness to accept such foods, and how that acceptance comes about. Nor have we analysed the role of the doctors or the health professionals. What is it or what should it be ?

About a year ago we carried out a study in London on the intention to breast-feed and the success of mothers in breast-feeding (Liebrich & Morley, 1976), at the same time analysing the attitudes of the staff attending these mothers, who should have helped the latter in their breast-feeding. Table 1 shows a trend in the answers given by women who intend to breast-feed disagreeing with such statements as ‘Nowadays it is no longer necessary to put up with the mess of breast-feeding when easily prepared milks are available’ and agreement (among the same group of mothers) with such statements as: ‘Breast milk is the best food for a baby under four months’.

I should like to discuss both the demographic and public health implications of the matters which have arisen at this meeting.

There are clearly some areas of consensus: we all agree that lactation is of fundamental importance, and that the birth interval is important, both for the health of the mother and child and with regard to fertility. Obviously, the longer the birth interval, the fewer births a woman will have during her reproductive life. A number of schemes were presented yesterday to show that in traditional societies with very long birth intervals there will be a reduced total fertility.

It is surprising that although the IPPF is 27 years old it has never previously had a meeting on this topic. On rational grounds, it is one of the first subjects at which it might have looked because many of the data we have discussed were available long ago. I remember reading about a Western doctor in Asia who saw the familiar scene of a mother with a young baby being suckled from one breast and an older child from the other breast but, in this case, the older one was also smoking a cigarette between sucks! Perhaps we need some kind of startling image like that to make us look closely at the role of lactation in fertility regulation.