A New Life Begins

Fertilisation

From puberty onwards a complex series of hormone signals and reactions stimulate one or other ovary to produce one egg a month until the menopause. A woman's cycle runs from the first day of one period to the first day of the next and is about twenty-eight days. When the egg breaks free from the ovary, usually around the fourteenth day of the cycle, this is called 'ovulation'. Filaments around the entrance to the Fallopian tube draw the egg into the tube and the rhythmic contractions of the tube waft it along towards the uterus. It takes four to five days for the fertilised egg to travel from the ovary to the uterus. If it is not fertilised it dies after one to two days and disappears, after which the lining of the womb, with its rich supply of blood vessels in preparation for a fertilised egg, begins to break down and is shed as a period at the end of the cycle. Although fertilisation normally occurs about two weeks later, doctors date pregnancies from the first day of the last menstruation period (LMP).

Sperm have a longer life than eggs: it is usually thought to be about three to four days, and it takes them about an hour to swim the seven inches from the cervix (neck of the womb) through the uterus to meet the egg in the Fallopian tube. Usually the tiny canal through the cervix (the os) is blocked with a plug of mucus and sperm cannot pass through. But when ovulation approaches, hormone changes make the mucus thin, opening the door to sperm. Some women can recognise this change in vaginal fluid so that they know when they are approaching a fertile period, while a few women actually experience some kind of pain at the time of ovulation itself. The egg is most easily fertilised twelve to twenty-four hours after ovulation because changes in its structure make it easier for the sperm to penetrate. Although every ejaculation contains several hundred million sperm, only one can fertilise the egg. When the egg and the sperm merge at fertilisation, the two halves of the chromosome set come together to form a complete set of forty-six again - one half from the mother and one half from the father ( For more on this click here)

Early Days of Life

Within about thirty hours of fertilisation the egg divides into two cells – the beginning of the complicated and amazing process of building a new person. By five days it has usually reached the sixteen-cell stage and has arrived in the uterus. It is now called a ‘blastocyst’ and, if all goes well, it will implant itself in the wall of the uterus. Sometimes mistakes happen and it implants in the wrong place, such as in the Fallopian tube. When this happens it is called an ‘ectopic pregnancy’. After about ten days the blastocyst has completely embedded itself in the lining of the uterus, but furious activity is going on within. The majority of the cells go on to form the placenta (called ‘chorionic villi’ during early development) and the membranes, whilst an inner cell mass becomes the embryo proper. The embryonic cells are divided into two layers. The first layer is the ectoderm, which makes the outer layer of the baby, skin, hair and nails, and will soon fold inwards to make the nervous system as well. The second layer is the endoderm, which makes all the organs inside the baby. In week three a third layer of cells, the mesoderm, starts to make the beginnings of muscles, blood, heart and bones.

Weeks 4–5 The unborn baby is technically known as the embryo now. Although only the size of a pea it has a primitive heart which begins to beat. Finger-shaped projections, the chorionic villi, have grown into the tissue of the uterine wall to anchor the embryo and a string of blood vessels connecting mother and baby will form the umbilical cord.

Weeks 6–7 Now about 6 mm (G in) long from crown to bottom, the unborn baby has limb buds which can move and will soon grow into arms and legs. The head is much larger than the body with a bump where the brain is forming and dents which will soon become ears. The eyes are still covered with skin which will be eyelids, and stay closed until about the 26th week.

Weeks 8–9 From nine weeks the unborn baby is called a ‘fetus’ and, although you may not have had your first antenatal check yet, all the internal organs are forming fast. He has tripled his size to measure about 2 cm (I in). Although the head is still much larger than the body, he is beginning to look more like a baby, and toes and fingers are starting to form.

Weeks 10–14 By 12 weeks your unborn baby is fully formed. All the organs are complete and he needs only to grow and develop. Finger- and toe-nails have begun to grow. He is about 7 cm. (2 Iin) from head to bottom and the top of the uterus, the fundus, can usually be felt beginning to rise out of the pelvis.

Weeks 15–22 Although your unborn baby will have been moving spontaneously from about week 12, he is usually not big enough for you to feel his movements until now. However, second-time mothers who recognise the fluttery sensations may notice them earlier. At 22 weeks the unborn baby is covered with a fine, downy hair called ‘lanugo’, which has usually been mostly shed before birth. A substance called ‘vernix’, a greasy, white protective film which is often still covering the baby born prematurely, has begun to form. Sometimes the baby’s sex can be detected at this stage with ultrasound scans.

Weeks 23–30 With modern technology it is possible for a baby to survive outside the womb from 23 weeks, although babies born at such a premature age have a high chance of handicap later in life if they do not die from complications of prematurity first. Once 26 weeks has been reached, babies delivered prematurely have about an 80 per cent chance of survival so long as they are looked after in a special care baby unit. Many will not be handicapped subsequently. With each additional week, the baby’s chances improve considerably. The downy lanugo has usually disappeared and the baby is covered in vernix. His movements are very clear and he still has plenty of room to manoeuvre, often turning complete somersaults. He may have regular patterns of activity and sleep, and some babies get hiccups which their mothers can feel. The baby may respond to sudden or loud noises by jumping or starting, and experiments seem to suggest babies can respond to soothing sounds like singing or music. He probably begins to learn the rhythm and pitch of his mother’s voice. At 30 weeks the unborn baby usually measures about 42 cm (16H in).

Weeks 31–40 With every extra week that passes, your baby has a greater chance of surviving if it is born early. The baby begins to fill out and become plumper and both the downy lanugo and vernix disappear. By about 32 weeks the baby has usually settled into the head-down position ready to be born. If his head moves down into the pelvis it is said to be ‘engaged’, but sometimes this does not happen until labour begins.