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Once every month or so the tissues lining the inside of the womb come away and are passed out through the vagina with some blood. This is called menstruation and is often referred to as "having a period". Each period can last from 2-8 days; 4-6 days is the average. Periods continue throughout a woman's reproductive life. Periods usually start between the ages of 12 and 15 years; this is known as the menarche. Periods usually stop altogether between the ages of 40 and 50 years; this is known as menopause. However, the age at which menstrual periods begin or end can vary.
The length of the menstrual cycle is the interval from the beginning of one period to the beginning of the next period (see Figure 4.1). It is usually about 28 days but can vary between 21 and 35 days, or even more. The length of each period, as well as the amount of bleeding, varies from woman to woman. It may also vary in the same woman from time to time. For the first couple of years that a girl has her periods, they may not occur regularly. The same is true for women who are going through menopause, when the periods gradually stop coming altogether. In addition, other factors such as illness, anxiety, or depression can speed up, delay, or prevent menstruation (see Chapter 20). A woman who is very thin or who exercises a great deal may also not menstruate regularly.
What causes menstruation? Menstruation only occurs when a woman is not pregnant. After a menstrual period, the lining of the womb starts to build up and prepare itself to receive a fertilised egg. If no fertilised egg reaches the womb within 2-3 weeks, the lining of the womb breaks down, and the bits of tissue leave the womb during the menstrual period about a week later.
When a baby is conceived and a fertilised egg reaches the inside lining of the womb, the breakdown of the womb's lining stops. Women do not have their periods during pregnancy, and usually the menstrual period does not start again until several months after the baby is born. Breastfeeding delays the return of the period even longer, depending on how often and how long the woman breast-feeds (see Chapter 15).
During a menstrual period, most women use clean cloths, sanitary napkins, or fresh tampons to absorb the blood. It is important to keep the outside genital area clean in order to avoid infections. It is not necessary to wash the inside of the vagina, since it cleanses itself naturally after each period. Washing the inside of the vagina, especially if harsh chemicals or soaps are used, can irritate the inside.
Figure 4.1: The Menstrual
Cycle
The average menstrual cycle lasts 28 days from the start of one period to the start of the next. The first day of the menstrual period is counted as "Day 1" of the cycle. A woman can get pregnant only if she has sexual intercourse just before ovulation, or the day she ovulates. In an average 28-day cycle, a woman can get pregnant if she has intercourse on days 11-14.
Each month, a mature egg is released from one of the ovaries; this is called ovulation. Once released by the ovary, the egg moves into the fallopian tube (see Figure 4.2). The egg can survive for only about one day (24 hours) in the fallopian tube. If it is not fertilised by a sperm within that time, it dissolves or flows out of the body.
Ovulation occurs in the middle of the menstrual cycle, or about halfway between periods (13-15 days before a woman's next period). Some women can tell when they ovulate because they feel a sharp pain on the left or right side of the abdomen (in the ovary), because they bleed a little bit from the vagina, or because the fluid that comes out of the vagina is clear and slippery. Since a woman can only become pregnant right around the time she ovulates, learning these signs of ovulation can help women identify their fertile time (see explanation of natural family planning in Chapter 17). However, it is often difficult to know when ovulation is taking place. For many women the only way to tell is when the period begins about 14 days after ovulation - or when they become pregnant!
For fertilisation to occur, the sperm must find the egg within one day (24 hours) of the time the egg leaves the ovary (see Figure 4.3). The sperm itself survives for 2-3 days (48-72 hours) within the woman's body. So fertilisation can occur if a woman has sexual intercourse during a five-day period - one, two, or three days before ovulation, the day of ovulation, or one day after.
While still in the tube, the fertilised egg begins to divide and grow. At the same time, it continues to move through the tube towards the womb. It takes an average of five days to reach the inside of the womb. Within two days of reaching the womb, the fertilised egg attaches itself to the lining of the womb. This process is known as implantation (see Figure 4.3).
THE PLACENTA (AFTERBIRTH) AND UMBILICAL CORD
After the fertilised egg is implanted, the lining of the womb where it is attached develops into thick, spongy tissue called the placenta. One side of the placenta is attached to the inside wall of the womb. The other side is attached to a structure called the umbilical cord, which connects the placenta to the baby (see Figure 4.4).
During pregnancy the placenta acts like a filter; it allows food and oxygen in the mother's blood to go through the umbilical cord to the baby. It also allows body waste from the baby to pass back through to the mother's blood. Chemicals called antibodies, which are produced by the mother to fight against certain infections, also pass through the placenta to the baby. These antibodies continue to protect the baby from infections for several months after birth. Some harmful substances such as germs which cause diseases like syphilis and rubella (German measles), as well as drugs, may also be passed to the baby through the placenta.
The fully developed placenta weighs around one pound (450 grams) at the time of delivery. After the baby is born, the placenta has done its job and is pushed out through the vagina; it is often called the afterbirth. The umbilical cord is no longer needed to nourish the baby, and can now be tied and cut. The stump is left to dry up and fall off (see Chapter 14).
Figure 4.2: The Process of
Menstruation
An unfertilised egg leaves the womb through the process of menstruation.
Figure 4.3: Fertilisation and
Implantation of the
Egg
Fertilisation marks the beginning of a nine-month process of growth and development in which a fertilised egg becomes a human baby. Before fertilisation, the egg is no bigger than the tip of a very fine needle. The sperm that unites with the egg is even smaller. Yet through a process of division, growth, and development, the baby at birth weighs around 6-7 pounds (about 3 kilos), many million times the weight of the egg and sperm from which it started.
Figure 4.4: Contents of the
Womb
During pregnancy the womb holds the foetus, the umbilical cord, and the placenta, which is attached to the inside lining of the womb.
Immediately after fertilisation the egg begins dividing in half. First it splits into two cells, then each cell splits into two again, until finally there are billions of different cells which make up the human body. As the cells multiply, they become specialised. Some cells grow into muscle, others become the brain, stomach, and other organs, while still others will become nerves, bone, or blood.
Human beings grow faster during the time in the womb than at any other time in life (see Figure 4.5). By the time the first period is missed, about two weeks after fertilisation, the new baby, called an embryo, already measures one-quarter of an inch (more than one-half centimetre). A bag of water has formed around the embryo and will protect it from bumping and external injury until birth. By the second missed period, the embryo is only about one inch (2½ centimetres) long, but the bones, muscles, nerves, eyes, ears, and major blood vessels can be identified. The heart is already beating and the liver, kidneys, and stomach have been formed, although they are not yet working.
After the third month, the embryo is called a foetus. By the fifth month, the mother can usually feel the foetus move. In general, during pregnancy the foetus moves, turns, swallows, urinates, sleeps, and responds to loud noises. Between the fifth and sixth months (approximately 24 weeks), the heartbeat is strong enough to be heard with a special instrument called a foetoscope.
By the eighth month or 32 weeks, the foetus weighs about 3½ pounds (1,500 grams) and is about 17 inches (40 centimetres) long. During the next two months, the baby grows and gains weight so that at birth the average baby weighs around 6-7 pounds (about 3 kilos) and is about 20 inches (50 centimetres) long.
Figure 4.5: Growth and
Development of the Baby Inside the Womb
The foetus grows rapidly inside the womb during pregnancy; by the time it is born it weighs 6-7 pounds (3 kilos) and is about 20 inches (50 centimetres) long.
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Summary: How Pregnancy Happens Pregnancy occurs when an egg from the woman is united with a sperm from the man, and the fertilised egg then attaches itself to the inside of the woman's womb. The steps involved in the development of pregnancy include: MENSTRUATION: Menstruation, or "the period", happens when the lining on the inside of the womb comes away and is passed out through the vagina with some blood. It occurs approximately once per month as long as a woman is not pregnant. Menstrual periods usually begin between the ages of 12 and 15 years, and last until the age of 40-50 years or so. A woman can get pregnant if she has sexual intercourse with a man about halfway between her periods, although this varies. OVULATION: Ovulation is the release of an egg from one of the woman's ovaries each month. FERTILISATION AND IMPLANTATION: Fertilisation occurs when the man's sperm unites with the woman's egg. The sperm must reach the egg within 24 hours of the time the egg is released from the ovary. Once fertilised, the egg begins to divide and grow. At the same time, it begins to move through the fallopian tube to the womb. When it reaches the womb it attaches itself to the inside. GROWTH AND DEVELOPMENT OF THE BABY: As the baby grows, the organs, nerves, muscles, and bones that make up the human body are formed. The growth of the baby inside the womb takes approximately nine months. At the beginning of this period the egg is the size of the tip of a needle; at the end, the average baby weighs 6-7 pounds. |
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