How babies are made
When girls and boys reach puberty, their bodies start to change and become more mature. From this time, if a male and a female have sexual intercourse (often called ‘making love’, or ‘sleeping with someone’), it is possible that the girl could get pregnant, ie. a baby could start to grow.
You may think you know how to make a baby: man meets woman, they make love and nine months later out pops a baby! But do you know exactly where sperm and eggs come from? Or how they find each other and combine to create a new life? Read on to discover the fascinating biological facts behind getting pregnant.
Inside the woman’s body: how an egg is hatched
For women, the possibility of pregnancy begins in the ovaries; those two small oval organs attached to either side of your uterus (womb). The ovaries are packed with eggs, which are made before you are even born. Every baby girl is born with up to 450,000 eggs in her ovaries. Many eggs begin dying off almost immediately and the rest steadily decrease in number as you get older. You’ll probably release about 400 eggs, during your fertile years. This begins with your first period and ends when the menopause arrives, usually between the ages of 45 and 55.
Each month, usually some time during the middle of your menstrual cycle, between one and three eggs start to reach maturity in one of your ovaries. The ripest egg is then released and is quickly sucked up by the tulip-shaped opening of the nearest fallopian tube (these are two four-inch canals leading from the ovaries to the uterus). This release is known as ovulation. The exact time of ovulation depends on the length of your cycle. In an average 28 day cycle, ovulation will most likely happen between the 12th and 15th days, counting day 1 as the first day of your last period. The length of your cycle, the ripening of your eggs and the timing of ovulation are controlled by several different hormones, which work together. See our article on your menstrual cycle for more about hormones.
The average egg lives and can be fertilised for about 12 to 24 hours after release, so it has to meet up with a sperm soon if a baby is to be conceived. If your egg does meet up with a healthy sperm on its way to the uterus, the two can join and begin the process of creating a new life. If not, it ends its journey at the uterus, where it disintegrates. When you have not conceived, the ovary stops making oestrogen and progesterone, the two hormones that would help maintain a pregnancy. Following the drop in the levels of these hormones, the thickened lining of your uterus is shed, along with the disintegrated egg, during your period.
Inside the man’s body: the making of a sperm
While women’s bodies are busy maturing a single egg at the leisurely pace of about one a month, men’s bodies are almost constantly at work producing millions of microscopic sperm. The sole purpose in life of each sperm, is to swim towards and penetrate an egg. While women are born with all the eggs they’ll ever need, men have to make sperm on a regular basis throughout their adult lives. From start to finish it takes about 64 to 72 days to create a new sperm cell. Since the average sperm lives only a few weeks in a man’s body, and as many as 300 million are set free with each ejaculation, this sperm factory is kept pretty busy.
In men, the same hormones that control ovulation in women stimulate the release of testosterone; the hormone responsible for producing sperm. Sperm production starts in the testicles, the two glands contained in the scrotal sac beneath the penis. The testicles hang outside the body because they’re quite sensitive to temperature. To produce healthy sperm they have to stay at a balmy 34 degrees C/ 94 degrees F; about four degrees cooler than normal body temperature. Once the sperm is created, it’s stored in a 40-foot long coiled tube in the testicle, called the epididymis until it’s scooped up and mixed with semen just before ejaculation.
Despite the millions of sperm that are produced and released in each ejaculation, only one can fertilise each egg. The gender of baby depends on which type of sperm burrows into the egg first; sperm with a Y chromosome will make a boy baby, and sperm with an X chromosome will make a girl. There are plenty of myths about how to conceive a boy or girl, and some are backed by a bit of scientific evidence, but on the whole, a child’s sex is determined randomly.
How Baby is Started
Sperm are the male ‘seeds’ that contribute to starting a new life – living sperm look a lot like tadpoles (under a microscope). When sperm are ejaculated (say ee-jak-u-lay-ted) from the penis during sexual intercourse, they swim up the vagina (vaj-eye-na), through the cervix (sir-vix), into the uterus (you-ter-us) and then into the fallopian (fal-o-pe-an) tubes of the female. These sperm are looking for an ovum (or egg) to fertilise.
When a female is born she carries thousands of ova or eggs ready to use when she becomes adult. These are the female ‘seeds’ that, along with sperm, contribute to creating a new life.
Once a month, the female releases an ovum (one to three eggs) .
If an ovum has been released, a sperm can unite with it, fertilise it and make the first cell of a new baby.
Once one sperm has fertilised the ovum, no other sperm can get in.
For the sperm it’s like a race and there is only one winner.
What Happens next
This fertilised ovum immediately divides into two cells, these cells then divide again and again over the next couple of days as the cluster of cells makes its way to the uterus (womb). Here it is planted in the lining of the uterus and continues dividing its cells to make billions of new cells. The female is now pregnant.
The amazing thing is that each one of these cells contains the same set of chromosomes or ‘plans’ that were created at fertilisation!
Over 9 months, these cells will grow into a new person – a baby.
Doctors have different names for this developing baby.
- 1 day – ‘zygote’
- first 2 months – ’embryo’
- 3rd month to birth – ‘fetus’
When your dad’s sperm and mum’s egg (ovum) got together, they each brought a set of ‘plans’ for what the new baby would be like.
When the ovum was fertilised and became your first cells, these ‘plans’ or genes helped to decide lots of things about you, eg. boy or girl, colour of skin, eyes, hair, etc.
Genes are made of DNA (‘de-ox-y-ri-bo-nu-cle-ic acid’, if you want the full name). If you could see your genes they would look like beads on a necklace of DNA. These strands are called ‘chromosomes’. Usually each cell in a human body has 46 chromosomes.
That first single cell has 23 chromosomes from mum and 23 from dad, which is why you might look like mum or dad (or grandparents) and have similar traits, eg. you and dad may have pointy ears, or you and mum can both wiggle your noses!
The chromosomes in a male are slightly different to those in a female. This is a picture of chromosomes in a male.
(Isn’t it annoying when people who haven’t seen you for a while say things like, “He’s got his dad’s chin”, or “she’s got grandma’s eyes!”)
Remember, any one sperm can only fertilise one ovum, so if 2 ova (eggs) leave the ovaries at the same time and are both fertilised then ‘non-identical’ twins are born. They may look alike or they may not, just like any brothers or sisters.
If an ovum splits after it has been fertilised, then you get identical twins because they have the same set of genes.
It is called a multiple birth if two or more babies are born at the same birth. Do you know what we call a set of three babies who are born at the same time? Triplets.
What Sex are you
What sex a baby will be is decided when the egg and sperm unite.
Each egg and each sperm have one sex chromosome.
There are two kinds of sex chromosomes – X and Y. Can you see why they are called x and y chromosomes? (Hint – look at the picture.)
Eggs carry only an X and sperm carry either an X or a Y
X+X means the cell will develop into a baby girl.
X+Y means that it will develop into a boy.
Once you are born, you will grow up into a unique human being – there’s no-one else like you in the world. Even identical twins are not exact copies of each other – they each have their own personalities.
You may look a bit like someone in your family, but there is only one of you!
You are a completely unique and wonderful person.
Inside the Womb
The place where the embryo plants itself is inside the uterus. The baby starts to grow, and other tissue grows into a placenta (say pla-sent-a).
During pregnancy (the time when the baby is growing in mum’s uterus), the placenta provides oxygen from the air that mum breathes, and nutrients (say new-tree-ents) from the food she eats.
This is why it is important that mum gets good food and takes care not to smoke, drink alcohol or take drugs, because the developing baby gets those too and he or she cannot say, “No”.
Some of the nutrients from what mum eats or drinks, and oxygen from the air she breathes, goes through the umbilical cord to the fetus. Any waste from the growing baby goes back through the cord into the mother’s bloodstream and passes out of her body.
The umbilical cord is a soft ‘bendy’ tube from the placenta to the navel (or tummy button) of the fetus.
There is a sac (like a bag of thin skin) filled with fluid protecting the skin of the developing baby. The baby can move around safely inside the mother for 9 months until he or she is ready to be born into our world.