From Conception to Birth

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A New Life

A baby begins its life when a sperm cell from its father meets an egg cell - an ovum (more than one are ova) - from its mother inside the mother's body.  When the egg is fertilized by the sperm cell, the two cells join together to form one new cell, which starts to grow and divide.  This is the beginning of the baby who will be ready to be born about 9 months later.

Egg cells come from the woman's ovaries.  About once a month, from puberty until the age of about 45, one egg is released from one of the two ovaries.  The egg then passes into one of the Fallopian tubes.  Tiny 'hairs' which line these tubes waft the egg down to the uterus (womb).  The uterus is a hollow organ with many blood vessels and strong, muscular walls.  Each month, the uterus lining thickens as it prepares to protect and nourish a fertilized ovum.  If it is not fertilized, an ovum dies after about two days.  The lining is now not needed, so along with the unfertilized egg and some blood, it passes out of the woman's body through the vagina.  This loss of lining, blood and egg is called menstruation, or a 'period'.  Menstruation is controlled by the female hormones progesterone and oestrogen.  After menstruation, a new uterus lining starts to form, ready to receive the next possible fertilized egg.

Sperm are made in a man's testes (one is a testis) from puberty onwards.  They are stored in a tightly coiled tube called the epididymus.  To pass to the woman's body, they travel to the penis through two tubes called sperm ducts.  Sperm swim in liquids made by glands (including the prostate) around the urethra - a tube that runs from the bottom of the bladder to the tip of the penis.  The mixture of sperm and liquids is called semen.  Both semen and urine are carried by the urethra, but muscles can close the exit from the bladder to prevent the two fluids from meeting.

Sperm enter the woman’s body during sexual intercourse.  The man's penis becomes stiff and fits inside the woman's vagina.  Semen, containing millions of sperm, is then squirted from the penis into the woman's body.  The sperm are then helped towards the uterus by muscular contractions of the uterus and ' vagina walls, although the sperm themselves can 'swim' by thrashing their tails.  It takes them about 2 hours to reach the Fallopian tubes, where fertilization usually occurs.  As many as 300 million sperm may start the journey, but only a few hundred reach the Fallopian tubes and only one sperm fertilizes the egg.  Fertilization, or conception can be prevented.

How a Baby Grows

Once a single sperm cell has penetrated an egg cell, no more sperm can enter.  The nuclei of the two cells merge (fertilization) and the fertilized egg travels down the Fallopian tube towards the uterus.  On the way down, it divides first into 2 cells, then into 4, then 8 and so on until a ball of at least 64 cells has been formed.

The ball of cells embeds itself in the uterus lining, which has thickened in preparation.  The baby develops very quickly.  After 4 weeks its heart begins to beat.  Some cells form the umbilical cord, which joins the baby to its mother through a special organ in the uterus called the placenta. 

Other cells form the amnion - a protective 'bag' filled with fluid.  This surrounds the baby and acts as a shock absorber to stop the baby - called an embryo at this stage - from being jolted.

After 8 weeks, the embryo is about 2.5 cm (1 in) long and is called a foetus.  After about 12 weeks, it has all its organs.  During the next 6 months, it grows larger and develops 'details' such as fingernails and hair.  At about the fifth month of development, the foetus begins to move its limbs and can be felt to kick.  At this stage the baby can hear, distinguish light and dark, swallow and suck its thumb.  Some unborn babies even get hiccoughs.  At about 6 months, the baby turns itself around in the uterus so that its head is pointing downwards - the position in which it is ready to be born.

The Placenta

The placenta develops at the place where the fertilized egg first embeds itself.  One side of the placenta is attached to the uterus wall.  The umbilical cord links the other side of the placenta to the baby.  It is through the umbilical cord that nourishment and oxygen pass to the baby from the mother's bloodstream.  Also waste products and carbon dioxide from the developing baby pass back to be disposed of by the mother's body.

Birth

After spending about 9 months developing inside its mother, the baby is fully formed and ready to be born.  The muscles of the uterus begin to contract.  These contractions get stronger and each one lasts longer, in order to push the baby out of the mother's body.  This is called labour.  The opening at the bottom of the uterus - the cervix widens so that the baby's head is pushed into the vagina.  Then the mother uses all her strength to push downwards and the baby's head emerges into the outside world. The umbilical cord is tied and cut by a doctor or midwife so that the baby begins life on its own.  It is the remains of the umbilical cord that form your ‘belly button'.

The time a baby takes to be born can be as short as 2 hours or longer than 24 hours.  After the baby has been born, the placenta is also pushed out of the body through the vagina.  The discarded placenta is often called the afterbirth.  Most babies are born head first, but sometimes babies do not lie head first in the uterus just before birth and so doctors may decide to open the mother's abdomen surgically and lift the baby out.  This is called a Caesarian section.

Most babies weigh about 3 kg (7 lb) when they are born and are about 500 mm (20 in) long.  The first thing a new-born baby does is to fill its lungs with air and cry.  Its lungs need to start working immediately in order to supply its body with oxygen.

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Stand: 06. Juli 2005.