The fertile years, although important, are only part of the human female’s total sexual life cycle. What begins in the womb seven months before birth continues past the menopause well into old age. It is in the teens, during puberty, that the changes taking place in girls might seem most pronounced.
A female’s sexual cycle begins in the womb, about two months after conception. Until then, the developing embryo is neither female nor male. Soon afterwards, the embryo will, in the case of a girl, start to develop ovaries in accordance with the genetic instructions received from a chromosome in the father’s sperm. The ovaries will then produce the female sex hormone, oestrogen, which will stimulate the development of the other female internal sex organs – the uterus, vagina and Fallopian tubes. Well before she is born, a baby girl’s reproductive system is complete and she has a full complement of egg cells in her ovaries.
Although a girl usually weighs less at birth than a boy, by the age of eight they are of equal weight, and at nine or ten she has overtaken him. She remains heavier until the age of 14, when the boy begins to outstrip her again.
In childhood, most girls are generally slightly shorter than boys of the same age, but between the ages of 11 and 13 they shoot up above their male contemporaries. At this stage, boys usually have extra years of steady growth before their own growth spurt, at about the age of 14, gives them a height advantage again.
The main difference between the sexes during childhood, however, is that the average girl matures physically more quickly than the average boy, usually reaching puberty between 11 and 13, some two years earlier than him.
Puberty is the process which changes a child into a sexually mature person. But sexually mature does not mean emotionally or physically mature and most young people will admit that in their early teens they are not ready for adult relationships or adult responsibilities.
Over the past hundred years, the average age of puberty has decreased in most western societies, perhaps because of better general health and improved nutrition. Although the onset of menstruation is only one sign of puberty – and a fairly late one – it does give some idea of the age at which girls are reaching puberty. Today, a girl’s first period usually occurs when she is about 12 or 13.
When a girl reaches puberty, her uterus and vagina enlarge rapidly, and she develops secondary sexual characteristics such as breasts and pubic hair. Her growth rate accelerates, and her body changes its proportions. Her pelvis and hips become wider, she loses her prominent childhood tummy and her waistline emerges. Shoulders and arms, legs, hips and buttocks become rounder and more fleshy.
These changes are triggered by the hypothalmus in the brain which, at a genetically predetermined time, instructs the pituitary gland to step up its production of growth hormone.
The pituitary gland also releases other hormones which stimulate the ovaries to begin manufacturing the sex hormones which transform a young girl into a woman capable of producing and breastfeeding a child.
The development of breast buds and enlargement of the areola – the area around the nipple – usually happen a year or so after menstruation starts, and takes about four years.
Gradually the breasts become fuller and more rounded and the nipples grow and begin to project.
Changes in girls during puberty. The Institute of Child Health in London has worked out a five-point scale for pubescent development. Each aspect of a child’s development is assigned a ‘score’ of one to five. This girl has developed pubic hair and breasts at the same rate, but this is not always the case.
Fine body hair usually begins to grow in the pubic area a short time after the breast buds develop, but in about a third of girls it precedes their development.
A little later in puberty, young girls’ underarm hair also starts to grow, and the pubic hair gradually becomes thicker, coarser and curlier.
External sex organs
During puberty, the mons veneris, the pad of fat which protects the pubic bone, becomes more prominent. Pubic hair first appears in this area, then gradually covers the outer lips, or labia majora, of the vulva, which become thicker, darker in colour and more sensitive to touch. The inner lips – the labia minora – which protect the vagina, also grow during puberty.
Greater hormonal activity results in an increase in vaginal secretions at puberty – this is nature’s way of ensuring that the vagina remains clean and healthy.
Later in puberty a number of girls experience skin problems. The hormonal changes which occur at this time can cause the sebaceous glands in the skin to secrete more oil than usual, blocking pores and causing spots and blackheads. This problem usually rights itself as the hormone balance is restored.
During puberty, girls also put on a considerable amount of weight, although this will be balanced by an increase in height. In the year before menstruation starts it is not uncommon to put on about 5.5kg. During each of the following two years the weight gain will probably be the same or slightly less.
When they start, periods are often irregular, sometimes occurring every few months. It may take a year or even longer before they settle down into a regular pattern.
Although puberty and adolescence overlap, adolescence usually lasts for longer. While puberty is the time of physical change which bridges the gap between sexual immaturity and maturity, adolescence is the transition between the safe world of childhood and the adult world of individual responsibility where much of what we do is our own choice.
As new sexual feelings begin to emerge at puberty, most young girls go through
a phase during which they hero worship, or have a crush on, a pop star, film actor or perhaps a schoolteacher of the same or opposite sex. By focusing their admiration on someone unattainable, the confusing emotions associated with their developing sexuality can be given a safe outlet.
Friends and lovers
In early adolescence, most girls and boys are happier with friends of the same sex. Strong attachments and, in some cases, sexual experimenting, between girls are quite normal at this time. Throughout their lives a few girls will continue to have their closest personal and sexual relationships with women, while the vast majority will eventually find that boys are more sexually attractive to them.
A woman is sexually mature once puberty ceases, her periods have become regular, she begins to ovulate and is capable of having a baby. But it may be a considerable time before she is mature in other ways.
Her fertile years will last from the end of puberty to the beginning of the menopause, when menstruation ceases.
The menopause and after
The menopause usually occurs between the ages of 45 and 55, although it may occasionally happen earlier or later. During this period of adjustment, known as the climacteric, production of sex hormones slows down so that ovulation occurs less frequently, and periods become irregular and eventually cease.
There is no reason why women in this age group should not continue to be sexually active. Many find that their sex lives actually improve during this time because they can concentrate more on their own needs and those of their partner, and they can enjoy lovemaking well into old age.