production in men. These hormones, or signalling molecules, are released from the man’s pituitary gland at the base of the brain.
The sperm’s journey
Follicle-stimulating hormone (FSH) stimulates the testicles to produce sperm – over 12 billion are produced each month. Luteinising hormone (LH) stimulates production of the male hormone testosterone within the testicles. Testosterone is essential for normal sperm production. After sperm are produced, they then have a long journey ahead before they are ready to fertilize an egg.
When they leave the testicles, they travel down a very fine coiled tube attached to the testicle called the epididymis, which is about 5-6 m (16-20 ft) long. Sperm entering the epididymis lack the ability to swim forwards, which is necessary to reach the egg. But as the epididymis sweeps them along, the sperm mature, so that by the time they reach the end of the epididymis, they have the ability to move or swim forwards. This whole process takes over 70 days.
Sperm are stored at the end of the epididymis. From there they flow into another tube, which connects the epididymis to the penis. This is called the vas deferens. This tube is about 30 cm (12 in)
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Cool sperm
Sperm develop better at a temperature slightly cooler than the main body temperature, which is one reason why the testicles lie outside the body in the scrotum.
long and is coated in muscle. The sperm are propelled along the vas deferens by muscular contractions, and along the way they are mixed with seminal fluid produced from glands prior to ejaculation. This fluid is rich in nutrients to help keep the sperm alive and healthy after they are deposited in the vagina. This mixture of sperm and seminal fluid is called semen. About 2-4 ml (½-1 tsp) of semen containing many millions of sperm is released when ejaculation occurs. However, the sperm don’t become completely mature until after ejaculation. It is only after ejaculation that they develop the capacity to break through the outer coating of the egg and fertilize it.
Conception
Normally a minimum of 40 million sperm are released with each ejaculation, but typically the quantity is over 80 million and often well in excess of 250 million. Although some are lost from the vagina, many make their way through the cervix (helped by the thin, watery mucous produced if the woman is fertile) into the womb and up into the fallopian tubes.
Egg meets sperm
The egg, having been released from the ovary, is picked up by the finger-like ends of a fallopian tube and transported down the tube. Fertilization of the egg occurs about one-third of the way down the fallopian tube. The egg is surrounded by sperm and eventually one sperm succeeds in penetrating the outer layer of the egg. This is the point of conception, after which no other sperm can penetrate the egg.
After conception, the genetic material (chromosomes) of the sperm and egg cells merge with each other and then the fertilized egg, which starts off as a single cell, divides to form two cells, then four, and then eight, and so on until a ball of cells is formed. This ball of cells continues its journey down the fallopian tube to the womb, where it stays for around three days, bathed in secretions from the womb.
About seven days after ovulation, it implants into the wall of the womb, whose lining has been prepared by the production of progesterone from the ovary. Another hormone, human chorionic gonadotrophin (hCG), is produced by the developing placenta. This maintains the production of progesterone from the ovary to help to support the early pregnancy. The ball of cells, once implanted, organizes itself into two different layers of cells, one that becomes the embryo and the other, the placenta.
Genetic make-up and conception
All cells in the body contain DNA (deoxyribonucleic acid), the substance that makes up your genetic code. For this reason, DNA is sometimes referred to as the ‘building blocks’ of life. This is what makes you what you are, the blueprint for the structure and function of your body. Everyone except identical twins has a different genetic code. Your genetic code is made up of thousands of genes that are carried on ‘chromosomes’. Each of us has 23 pairs of chromosomes in every cell in our body – a total of 46 chromosomes per cell. Of the 23 pairs of chromosomes in every cell, 22 pairs are ‘general’ chromosomes and one is a pair of ‘sex’ chromosomes.
Sperm and eggs are an exception to this general rule. An egg from a female has only 23 chromosomes; 22 of these are ‘general’ chromosomes and one is a ‘sex’ chromosome. The sperm from the male also has only 23 chromosomes: 22 general chromosomes and one sex chromosome. When conception occurs and the sperm fertilizes the egg, the egg and sperm cells fuse. A fertilized egg therefore has the full complement of 46 chromosomes and the baby that grows from the egg has 46 chromosomes in every cell.
The sex of the baby conceived is determined by the ‘sex’ chromosomes – referred to as ‘X’ and ‘Y’ chromosomes – and the way these combine determines whether we are male or female. All girls have two X chromosomes and no Y chromosome, while a boy has one X and one Y chromosome. It is the sex chromosome that comes from the father’s sperm that determines the sex of your baby. The mother has no power to influence the sex of the baby because she can contribute only an X chromosome, whereas the father can contribute either an X or a Y chromosome.
Sexual position and conception
Provided intercourse is comfortable and semen is deposited at the top of the vagina, the sexual position should not influence conception. However, it is perhaps best for the woman to avoid more upright positions after the man ejaculates to prevent some of the semen draining out of the vagina, although there is no evidence that resting after intercourse increases the likelihood of pregnancy. Equally, there is no truth in the old wives’ tale that you can’t get pregnant if you have intercourse standing up.
Age and conception
There is no ‘ideal’ time to get pregnant. Fertility varies from person to person, although fertility in both men and women reaches its peak at about the age of 24 years. Many women are now delaying pregnancy until their 30s and even 40s where, once over the age of 35, they are at greater risk of developing complications such as high blood pressure during pregnancy. If you are over 35 years old, there is also a higher risk of chromosomal problems in the fetus, such as Down’s syndrome.
It is not just older mothers who are at increased risk of problems. The risk of complications is also higher if you have a pregnancy when you are a teenager. So, from the doctor’s perspective, having your babies somewhere between the age of 20 and 35 is best in order to minimize the risk of complications, some of which can be serious. However, you may not be at a stage in your life when you can have your babies at that time. So do remember that the majority of women over 35 have a successful pregnancy outcome. It is important to keep these extra risks associated with age in perspective, but seek medical advice if you have any particular concerns and, in particular, if you have an existing medical problem. The ‘best’ time to become pregnant depends largely on what is best for you and your partner, taking into account and weighing up everything that is going on in both your lives and thinking about what pregnancy will mean for you.
Every woman knows that it is really important to take good care of her health when she is pregnant. But many women are not aware that their health before pregnancy is critical to producing a healthy baby. This means that you need to think about your health and, in particular your diet, not just after that positive pregnancy test, but for several months before.
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