Planning a pregnancy

Getting pregnant

Conception occurs when a man’s sperm fertilises a woman’s egg. To understand conception and pregnancy, it helps to know about the male and female sexual organs, and to understand the physical process behind a woman’s monthly cycle and conception itself.

The male sexual organs

The penis is made of erectile tissue. This tissue acts like a sponge and, when it becomes filled with blood, the penis becomes hard and erect.

The testes are contained in a bag of skin that hangs outside the body, called the scrotum. It helps to keep the testes at a constant temperature, just below the temperature of the rest of the body. This is necessary for the sperm to be produced. In heat, the scrotum hangs down, away from the body to help keep the testes cool. When it is cold, the scrotum draws up closer to the body for warmth.

Two tubes, called the vas deferens, carry sperm from the testes (testicles) where sperm are made, to the prostate and other glands. These glands add secretions that are ejaculated along with the sperm.

The urethra is a tube that runs down the length of the penis from the bladder, through the prostate gland to an opening at the tip of the penis. Sperm travel down this tube to be ejaculated.

In this section

The female sexual organs

A woman's reproductive system is made up of both external and internal organs. These are found in what is usually referred to as the pelvic area, or the part of the body below the tummy button.

The external organs are known as the vulva. This includes the opening of the vagina, the inner and outer lips (labia) and the clitoris.

The woman’s internal organs are made up of:

Pelvis: this is the bony structure around the hip area, which the baby will pass through when he or she is born.
Womb or uterus: the womb is about the size and shape of a small, upside down, pear. It is made of muscle and grows in size as the baby grows.
Fallopian tubes: these lead from the ovaries to the womb.
Ovaries: there are two ovaries, each about the size of an almond. They produce the eggs.
Cervix: this is the neck of the womb. It is normally all but closed, with just a small opening through which blood passes during the monthly period.
Vagina: the vagina is a tube about 3in (8cm) long. It leads from the cervix down to the vulva, where it opens between the legs. The vagina is very elastic so it can easily stretch around a man’s penis, or around a baby during labour.

Hormones

Hormones are chemicals that circulate in the blood of both men and women. They carry messages to different parts of the body, regulating certain activities and causing certain changes to take place.

The female hormones, which include oestrogen and progesterone, control many of the events of the monthly cycle, such as the release of the egg from the ovary and the thickening of the womb lining.

Once conception has occurred, the amount of oestrogen and progesterone increases. This causes the womb lining to build up, the blood supply to the womb and breasts to increase, and the muscles of the womb to relax to make room for the growing baby.

The woman’s monthly cycle

Every month one of the ovaries releases a ripe egg (occasionally two). This is called ovulation. The egg then makes its way into the fallopian tube. At the same time the lining of the womb thickens and the mucus in the cervix becomes thinner, to make it easier for the sperm to get through.

The ripe egg then travels slowly down the fallopian tube, and it is here that it may be fertilised by a man’s sperm if you have sex at this time. By now the lining of the womb is thick enough for a fertilised egg to implant in it.

If the egg is not fertilised it passes out of the body through the vagina, along with the lining of the womb, in the monthly period of bleeding.

Conception

A woman is most likely to conceive just after the time when she ovulates when an egg has been released from one of her ovaries. Sperm are ejaculated from a man’s penis into the woman’s vagina during sex. In one ejaculation, there may be more than 300 million sperm.

Most of the sperm leak out of the vagina again, but some begin to swim up through the cervix. Because the mucus in the cervix is thinner than usual during ovulation it’s easier for the sperm to pass through. The sperm swim into the womb and so into the fallopian tube. One sperm then joins with the egg and fertilises it. Conception has taken place.

During the week after fertilisation, the fertilised egg, or embryo, moves slowly down the fallopian tube and into the womb. It is already growing. The embryo attaches itself firmly to the specially thickened womb lining. Hormones released by the embryo and by the woman’s ovary prevent shedding of the womb lining. The woman misses her period.

The best time to get pregnant

An egg lives for about 12–24 hours after it is released from the ovary. If conception is to take place it must be fertilised within this time. Sperm can live for several days inside the woman’s body. If you make love a day or so before ovulation, the sperm will have time to travel up the fallopian tubes and will be waiting when the egg is released. So the chances of conception are highest if you have sex on the day before ovulation.

It is difficult to pinpoint exactly when ovulation happens, unless you are practising fertility awareness (see External links). But in most women ovulation usually happens 10-16 days before the start of the next period. The menstrual cycle is counted from the first day of a woman’s period – day one. Some time after her period she will ovulate, and then 10-16 days after this, she will have her next period. The average cycle takes 28 days, but shorter or longer cycles are normal.

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