Getting Pregnant

Getting Pregnant (Baby Making 101)

The birds and the bees!

You were probably taught all this back at school, but how much information you actually absorbed while giggling at the text book images of human genitalia is anybody's guess. You may well have forgotten the details about the way in which a sperm and egg meet, fuse and create a new human life. Read on to learn more about the biological process of becoming pregnant.

The reproductive system

Girls are born with two ovaries that contain about 3 million eggs. From day one the eggs start to die off and by puberty there are only around 400,000 left. On average, a woman will release only 400 to 500 eggs during her fertile years (between her first period and menopause). The average age of menopause in the UK is 52.

When an ovary releases an egg, it travels down the fallopian tube and into the uterus (womb). The uterus is connected to the narrow cervix which in turn is connected to the vagina.

Sperm need to negotiate their way through the vagina and cervix and travel up the fallopian tube to meet the egg. It is here that the egg must be fertilised by a sperm for a baby to be conceived.

How ovulation happens

Ovulation takes place in only one ovary at a time, with each ovary releasing one egg (or sometimes more than one) in alternate menstrual cycles. In each menstrual cycle, up to twenty eggs start to reach maturity in a fluid-filled bubble (called a follicle) inside the ovary. Usually, only one 'dominant' follicle becomes fully mature, it ruptures and the egg bursts out (ovulation). The others shrivel up and the eggs inside are lost.

Ovulation commonly happens around 12 to 14 days before the start of your next period. An egg will survive for 24 hours after it has been released - so you only have a short 'window of opportunity' for the egg to be fertilised by a sperm to make a baby (conception). If the egg doesn't fuse with a healthy sperm, it will disintegrate in the uterus.

If you have not conceived, the ovary will stop producing the hormone progesterone that would have helped thicken the lining of the uterus to enable a fertilised egg to implant there and maintain a pregnancy. When progesterone levels drop, the lining of the uterus is shed, along with any remains of the unfertilised egg, and your period begins. Your period signals that a new cycle of follicle growth can begin again in the other ovary.

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The man's role in conception

Your partner's role may seem like the easy bit, but actually the process that his sperm have to go through in order to fertilise your egg is mind-boggling. When a man orgasms he ejaculates, on average, about a teaspoon of semen, which contains between 100 and 300 million sperm. Less than 100,000 will make their way through the cervix. Around 200 make it into the fallopian tubes and only one sperm will be able to fertilise the egg.

Unlike girls' reproductive systems, boys are not born with a ready-and-waiting supply of sperm. Sperm production starts around puberty and from then onwards sperm are made at a rate of 1,500 every second. Each sperm will live for about 10 weeks and so sperm must be made regularly.

Sperm is made in the testes, which are inside the testicles - the two glands in the scrotum that hang under the penis. The testicles are kept outside of the body because they are very sensitive to temperature and must be kept cooler than normal body temperature to make healthy sperm (at a constant 34 degrees centigrade). The newly-made sperm is delivered into the epididymis (a long coiled tube sitting at the top of each testis). During the next 2 to 3 weeks the sperm mature, becoming capable of moving on their own and fertilising an egg. The matured sperm move into tiny tubes called the vas deferens. These tubes contract as the man orgasms and transport the sperm out of the scrotum into the urethra (the tube that runs between the bladder and the penis). The sperm are mixed with semen (a sugary fluid to give the sperm energy for the journey ahead). When a man ejaculates, his bladder opening shuts off and the sperm travel rapidly into his penis. The semen is forced out, at a speed of 10 miles an hour, into the woman's vagina.

The sperm's long journey

The sperm have made it into the vagina, but this is just the start of their long race to reach the egg. They meet with a pretty hostile environment in the vagina - it is acidic to protect the uterus from infections. In the vagina, the semen quickly clumps together to help keep the sperm in the right place and give them the best defence against the acidity. Luckily, around ovulation, your body does give the sperm a helping hand. Your vaginal mucus is at its most fertile - it looks like raw egg whites and is slippery, clear and there is lots of it. This helps the sperm travel speedily through the mucus towards the cervix.

The sperm will have to travel a distance of about 18 centimetres from the cervix, through the uterus, to the Fallopian tubes. It may sound like a short distance, but it is the equivalent of a human swimming more than 100 lengths of an Olympic-sized swimming pool. The fastest sperm can reach the egg in as little as 45 minutes, with the slowest swimmers taking around 12 hours.

5 to 10 minutes after ejaculation, some sperm will have already reached the uterus and will be making their way towards the fallopian tubes. For the next 72 hours sperm will be following on behind, but many will get stuck or lost along the way and will not survive. Once they reach the fallopian tubes, the remaining 200-or-so sperm swim upwards, helped by gentle muscular contractions in the uterus and tubes. Your body is multi-tasking at this point, because the egg is also being propelled downwards towards the uterus at the same time.

For the handful of strongest sperm that make it to the egg, they've still got a lot of work to do. Several sperm may bind to the surface of the egg and so each must work frantically to wriggle through the egg's membrane. Cleverly, the sperm release enzymes to help digest the membrane. When the winning sperm makes it through, fertilisation occurs! The egg immediately forms a thick jelly-like coat around itself to prevent any other sperm from getting in.

Your pregnancy has begun

The single cell now begins to divide to create more cells. It splits in two, then those cells each split in two, and so on. By the third day there will be around twelve cells. This tiny bunch of cells is called a blastocyst and it will take about 60 hours to drift its way to the uterus, by which time it will have divided into about sixty cells.

Roughly a week after fertilisation, the blastocyst sheds its jelly-like coat and attaches itself to the lining of the uterus. Once the blastocyst has embedded itself, you are pregnant. At this point the pregnancy hormone HCG (human chorionic gonadotrophin) is produced to signal to the body to carry on producing progesterone. This prevents the lining of the uterus from breaking down so that you will not have a period.

Although you won't even know that you are pregnant yet, in the second week after fertilisation, the cells will start to develop into an embryo. By now, there will be about 200 cells, with the inner cells making the embryo while the outer cells will become the placenta (to sustain the baby) and the amniotic sac (that keeps the baby surrounded by lovely, warm amniotic fluid). The embryo is only a tiny dot at this stage, but the sex of your baby, the colour of its eyes and hair, and how tall it will grow have already been decided due to the genes it has inherited from both its parents.

Occasionally, the blastocyst can embed itself somewhere outside of the uterus (usually in the fallopian tube), but a pregnancy cannot survive outside of the womb. This is called an ectopic pregnancy and is a medical emergency because there is a risk that a fallopian tube could burst.

I'm pregnant!

You may not realise you are pregnant until you miss your period. You might start to notice that you are feeling a bit tired and emotional, your breasts might be sore or swollen, you may need to go to the toilet more often than normal and you may have a really strange metallic taste in your mouth. Read more about the symptoms of pregnancy here.

The best way to confirm that you are expecting a baby is to take a pregnancy test, either at home, or at the GP's or family planning clinic. The test detects the levels of HCG in your urine and you will get a result within minutes. Make an appointment to see your GP as soon as you know you are pregnant. Your doctor will advise you about your local maternity services and will put you in contact with your community midwife. You will usually see your midwife for the first time when you are between 10 and 12 weeks pregnant. You will have your first ultrasound scan around this time too. This is when you will see your tiny baby for the first time.

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This internet site provides information of a general nature and is designed for educational purposes only. If you have any concerns about your own health or the health of your child, you should always consult a doctor or other healthcare professional.