Before relating somatic growth and maturation to genital maturation, we should present a concept of growth that is sometimes a little difficult to conceive. The most important basis in studying human growth is the fact that it is a continuum, and does not start at birth, but at conception. This continuum rarely moves at a constant speed. We are so used to thinking in terms of size attained: the average measure of head circumference at 3 months of age in health, for example. Yet to consider growth as movement leads us to think in terms of velocity; that is, how fast, or slowly, is an individual child growing.

Puberty is defined in the Oxford English Dictionary as the state or condition of having become functionally capable of procreating offspring, suggesting that it is a discrete event that occurs at a particular point in time. Whilst it is easy to determine the age at puberty in animals from the time of completion of spermatogenesis in the male, or the first ovulation in the female, these are particularly difficult criteria to evaluate in our own species. Thus human puberty is generally described in terms of a sequence of changes in secondary sexual characteristics occurring over an extended period of time, and these have been reviewed in detail by Marshall & Tanner (1974).

Sensory stimuli from the external environment (e.g. visual and olfactory stimuli, stress) or internal stimuli cause brain nerve fibres to release neurotransmitters (catecholamines, indolamines and cholinergic agents). These neurotransmitters regulate the secretion of gonadotrophin-releasing hormone (GnRH) from neurosecretory cells of the hypothalamus (Kamberi, 1975). It would seem that under the proper steroid environment, catecholamines (dopamine, norepinephrine or epinephrine) and the cholinergic agent acetylcholine exert a stimulatory influence, whereas indolamines (serotonin or its metabolic product, melatonin) have an opposite effect. In turn, GnRH reaches the anterior pituitary via the hypophyseal portal system, and, through the mediation of cAMP [though may be not as an obligatory intermediate (Naor et al., 1975)], controls gonadotrophin secretion (Labrie et al., 1974).

Urinary oestrogen and pregnanediol values were measured in 24 boys and 38 girls between the ages of 2 and 13 years. Longitudinal studies were conducted on eight girls, two of whom collected for periods of 4 and 5 years which included menarche and in one case establishment of ovulation. Highly sensitive assay methods were developed for measuring the very small amounts of oestrone, oestradiol and oestriol and pregnanediol present in the urine of young children. The total oestrogen values were within the submicrogram range of 0·1–0·5 μg/24 hr in the children aged 2–8 years, with no differences seen between the boys and girls. After the age of 8 years, oestrogen values above 1 μg/24 hr began to be encountered and by age 11½ years the majority of subjects were recording oestrogen values above this figure. The rise in the oestrogen values was more rapid in the girls than in the boys. Evidence was presented that a value of approximately 1 μg/24 hr represents the minimum oestrogen production for the initiation of breast development. The oestrogen values were fluctuating with irregular periodicities at all ages and the gradual general rises seen after the age of 8 years could be arrested at any stage for a year or more. Menarche was preceded by marked periodic fluctuations in oestrogen output which peaked above 15 μg/24 hr. In all subjects studied, the initial bleeding cycles were anovulatory as judged by the low pregnanediol values, the usual pattern being one of fluctuating oestrogen production. One subject was studied fully through to the establishment of ovulation, which first occurred 12 months after menarche. The approach of ovulation was indicated by pre-menstrual rises in pregnanediol which increased in amplitude from 0·4 mg/24 hr until finally 2 mg/24 hr was exceeded (the value accepted for ovulation). Evidence was presented that the interval from menarche to ovulation in different individuals was very variable, extending from ovulation at menarche itself to periods of more than a year. Recording of self-observed symptoms of production of cervical mucus could be of considerable value in documenting these events in larger populations.

There have been substantial changes in the pattern of pregnancies to teenagers in England and Wales in the past 25 years. The number of births and abortions to teenagers has increased until the last 2–3 years since when there has been a decline. This paper looks at the changes that have occurred in the population structure and marital patterns of teenagers during these years, and examines teenage pregnancies and their outcomes with regard to some of the medical and social factors that may have influenced these changes.

The publication in 1976 of a 64-page pamphlet with the unlikely title 11 Million Teenagers: What Can Be Done About the Epidemic of Adolescent Pregnancies in the U.S. (AGI, 1976) precipitated a dialogue quite new to the American public. For the first time, attention was centred on the fact that pregnancy among teenagers was almost as prevalent as the common cold and that those who were getting pregnant increasingly were younger, and more of them were white and middle class. The figure of one million pregnancies experienced by women aged 15–19 showed that one in ten female adolescents and one out of four sexually active teenagers are conceiving each year.

Pregnancy in adolescence is now a very great concern for doctors, teachers and social workers throughout the world and yet about 95% of the publications on this topic have come from the USA. The remainder are mainly from the UK and Scandinavia. Other countries have produced only a small number of papers, focusing mainly on clinical problems such as the pathological events and complications during pregnancy or delivery. In France, the first paper to appear in a paediatric journal was published in 1977 in the French journal of school health (Martin, 1977). On the other hand, teenage magazines often contain articles about sexual behaviour and pregnancy in adolescence. There is now a great concern in the adolescents' press about the problems of sexuality, contraception, abortion and pregnancy, including advertising for pregnancy tests.

There is little statistical information from developing countries on the prevalence of early and late teenage pregnancies and associated health and psychosocial sequelae. Developing countries cannot be studied as an entity since they differ widely in terms of cultural background, religion, traditions, etc. However, characteristics of an underprivileged situation are: an early reproductive debut, high fertility and close spacing of pregnancies, and high maternal and infant mortality. The high maternal and infant mortality rates are related to socio-economic parameters but also specifically to the age of the mother, being increased for mothers under the age of 20, particularly for the younger ones and when there are repeated teenage pregnancies. Low minimum age of marriage for girls, typical of many developing as well as developed countries, means a consent of society for early family formation.

Epidemiological studies and studies on changing reproductive behaviour in situations undergoing modernization processes are required to estimate the magnitude of the problem from health and psychosocial aspects, and in order to design appropriate services.

During the last 10 years an increasing number of pregnancies have been noted in adolescents. The children of these pregnancies are often at risk. The problem was discussed in a meeting on Pregnancy and Abortion in Adolescence in 1974, held at WHO headquarters, Geneva. An annotated bibliography was prepared for that meeting, from which this review originated. The literature covered a wide range of subjects, but an attempt has been made in this review to discuss the problem in six main sections: social aspects; sexual attitudes and behaviour; sex education and information; contraceptive services for adolescents; medical and clinical aspects and legislation. Quite a number of teenagers are sexually active even in their early teens but often keep to one partner. Their use of contraception is poor, partly because of a lack of education and information. Young people are demanding better information and services, which would probably best be provided through special teenage clinics. So far, there have been very few investigative studies dealing exclusively with adolescent use of different contraceptive methods. Methods of contraception available at present are often unsuitable for use by adolescents, and further research on the problem is needed.

There is a mass of evidence supporting the belief that adolescents are sexually active but do not use contraception, or do not use it effectively. There are a number of factors which may account for this:

(1) a belief in spontaneous behaviour; (2) lack of acceptance of their sexuality by themselves and by others, especially their parents and their teachers; (3) inadequate sex education; (4) inhibitions about obtaining contraception and actual difficulties encountered.

These headings are very arbitrary since all these factors are inter-related and it is difficult to know where to start.

A recent report by the Brook Advisory Centres, refers to the fact that in girls under 20, the numbers of illegitimate births and abortions have not shown any decline in the period 1966–77. It is also estimated that half the 40,000 teenage brides who marry each year are pregnant when they do so. It seems appropriate therefore, at this time, to look at the social and emotional factors that contribute to this situation.

For those interested in the patterns of adolescent fertility there is a lesson to be learned from the story about the Emperor's new clothes (Andersen, 1913). The problems, or lack of them, present themselves as starkly as the Emperor's, yet there is a tendency not to face the fact that in certain societies adolescent sexuality can create problems. The vast majority of parents, health personnel and policy makers seem to prefer to ignore what can be readily perceived. Conversely, in many areas of the world, there may be a tendency to announce the existence of problems which do not exist.

In the past 20 years at least 54 countries have passed legislation setting or raising the minimum age at marriage. How successful this legislation will be is questionable, especially when it runs counter to prevailing social and cultural institutions and beliefs, but it does reflect the growing international concern with delaying marriage. The deleterious consequences of early marriage are most evident in high birth rates and low status of women, both of which prevent poor countries from developing. Concern for postponing marriage has evolved from the larger objectives of stemming population growth and of guaranteeing women their basic rights. To raise the standard of health and education of the mother thus improves the welfare of the family.

In my professional work I could not escape the realization that a major part of human suffering arose out of ignorance of simple facts, unquestioning acceptance of tradition, and unhealthy social pressures. This realization made me plunge into the stormy waters of human sexuality and sex education of young people in particular. To them I gained personal access, as well as access through mass media. The response I received from our target population was most gratifying. The bulk of the material I now present was derived from some of the responses.

The population of African countries, typical of developing countries, is characterized by the large proportion of children and young people. An almost perfect pyramid illustrates the age distribution of Ghana's population (Text-fig. 1).

Projections of future population point to a further rise in the proportion of children (0–15 years of age) from the present 45% to 47–49% by the year 1980. The children of today will be the parents of tomorrow and for the adolescents the statement can be taken literally; the study of adolescents and their sexual and fertility problems, therefore, needs urgent attention. Especially in black Africa, these problems cannot be studied in isolation from the traditional, cultural and socio-economic environment. Indeed much of the psychosexual trauma of this group is closely interwoven with their complex backgrounds.

Concern about the health of adolescents, their patterns of social and sexual interaction as well as the ways in which they ultimately are able to adapt to the outcomes of their interaction is a relatively recent development (Carballo & Engstrom, 1975). In no small way the concern currently being addressed to this issue is indicative of a much broader preoccupation with the impact of social change on individual and community health in general. For while adolescents, because of their particular position in modern and modernizing societies, have possibly presented more socially dramatic manifestations of the effects of a new environment on lifestyle and behaviour, they have not been alone in experiencing these social change influences. Many of the ambiguities, stresses and needs of modern society have produced, in one way or another, health and psycho-social problems among other age groups too.