L ong before a woman is aware she is pregnant, the fertilized egg she is carrying has already started to grow very rapidly. When a sperm fertilizes an egg it creates one complete cell — a tiny unit which contains all the genetic material to develop into a fully formed human being. The cell keeps dividing until in seven days it has grown into a clump of several hundred cells. Each of these continues to carry the complete genetic code which will determine the development of the baby- this is vital, for if the code is incomplete some kind of imperfection or abnormality will appear later on.
As the fertilized egg divides it passes down the Fallopian tube towards the. At the same time, the lining of the prepares to receive the egg: it grows thicker, nutrients are laid down in the cells and changes take place in the glands, making them ready to produce the amniotic fluid which will surround the foetus in the . It takes about 4-6 days for the fertilized egg to reach the womb, where it sticks to the wall and buries itself into the lining. At this stage, there will be a if the egg fails to get a firm anchorage.
The term embryo is used to describe the fertilized, developing egg, up to the point when all the organs are formed. A foetus is considered to be a fully formed minute human being. So an embryo becomes a foetus after about 10 weeks.
An essential exchange station lies between the unborn child and its mother, known as the This vital link starts to develop once the egg is embedded in the lining of the womb. Cells from the outer edge of the embryo form a mass of fingerlike projections which contain minute blood vessels. These invade the mother’s tissues and develop into the placenta- it’s rather like a thick plate or disc clamped onto the inside of the womb. By the time the baby is full term this is about 9 inches in diameter and an inch thick. The ‘fingers’ in the placenta are bathed in a pool of the mother’s blood; the placenta is linked directly to the foetus by large blood vessels which run along the umbilical cord. So, when nutrients and oxygen from the mother’s blood pass into the blood vessels of the placenta they are channelled through to the foetus. Waste products from the foetus can pass back into the mother’s circulation in a similar way. The placenta is expelled shortly after the baby is born – hence the popular name ‘after’.
The foetus grows inside a sac (a bag of membrane) which is filled with amniotic fluid. The fluid has several functions; if the mother falls or bangs her abdomen against something, it will absorb some of the shock and so protect the foetus. It also helps to maintain an even temperature around the foetus, and provides a comfortable, sterile environment where the foetus can move its limbs freely. By the end ofthe amount of fluid varies between 1 and 4 pints.
The foetus grows very rapidly indeed – if a child were to continue growing at the same rate afteras before, it would be 75 feet tall and weigh several tons by the age of 19 years!
Different parts of the foetus grow at different rates. Most of the blood which contains oxygen is pumped to the head area of the foetus, so the brain and head grow most quickly. In the early stages ofthe foetus appears to be almost all head and, even at , a baby’s head still looks disproportionately large for the size of its body.
The limbs are of little use inside the womb so they have a relatively poor blood supply- at birth they are rather puny in relation to the rest of the body. It’s not until the baby starts to toddle that the legs become stronger and grow longer than the rest of the body.
Usually a mother first feels her baby move during the 18th to 20th week of pregnancy. However, the foetus has been moving much earlier than this – a doctor using an ultrasound machine can detect movements at about 8 to 10 weeks. Pregnant women should write down when they first feel the baby move, as this may be useful later in deciding exactly what date the baby is due.
In the early stages of development there is simply a ‘tube’ which will eventually develop into the baby’s heart. But research has shown that there are pulsations in the tube as early as 22 days after– that’s about 5 weeks from the first day of the last normal menstrual period. These pulsations can be detected at about 14 weeks using a hand-held ultrasound machine, and a bigger hospital ultrasound instrument might pick them up a week or two earlier. The human ear can usually hear the baby’s heart beat, through a special stethoscope, at about 20 weeks of pregnancy.
The embryo is most likely to be dislodged at the time when a period would be expected — at Weeks, 8 weeks, or 12 weeks after the first day of the last normal period. If a pregnant woman notices any loss of blood, however slight- even brown staining from old blood – at these times she should stay in bed and contact her doctor. Most miscarriages which occur in the early stages are caused by the embryo being abnormal.
The average length is about 20 inches (50cms) and boys are often a little longer than girls. The average weight of a full-term normal child is pounds (3-3.5 kilograms), with boys usually weighing a little more than girls. But a baby who is under this weight at birth is not necessarily abnormal or premature. Taller mothers may expect to have slightly longer.
A newborn child has a layer of fat beneath its skin which makes it look quite rounded. In the first weeks of pregnancy an external layer of fattv material protects the baby from loss of tempera-ture, but proper fat is not laid down until the last six weeks of pregnancy. A premature baby has not had time to lay down much fat and so will have wrinkled skin and look rather wizened.
If you could actually see the foetus around 12 weeks it would already be clear whether it’s going to be a boy or girl. Testing this from the ‘outside’ is not quite so straightforward. The only reliable method of checking the sex while the baby is in the womb is to examine the chromosomes in the baby’s cells – these are shed from the baby s skin into the surrounding fluid. The test involves passing a needle through the stomach wall into the womb to draw out fluid and to collect some of the cells. They are then processed and examined under a microscope.
This is only done after about the 16th week of pregnancy, since there would be too few cells before this time. There is a risk of causing a miscarriage, so if s only done for medical reasons, not just to satisfy the curiosity of impatient parents! A doctor might want to know the sex of an unborn child if he suspected it was carrying a sex-determined disease, such as haemophilia.
Later in pregnancy (30 weeks) an ultrasound scan of the foetus may show up a scrotum on the ‘picture’. However, this is difficult to achieve as it depends on the ultrasound beam travelling in the exact plane between the baby’s legs. For this reason it is not commonly used as a method of determining sex.
Another way of testing may be to detect the very small amounts of a male hormone which pass into the mother’s body fluids (blood or saliva) if she is carrying a boy. If thesecould be detected with certainty they might give an indication of a male child, but work on this test is still at an early stage and is by no means conclusive.
It is often thought that male and femalehave a different heart rate at the foetal stage, but most doctors will not suggest it as a guide to indicating the sex.
There are various techniques nowadays which can help to give an idea of how the foetus grows and responds inside the mother’s body. Some of the techniques, such as ultrasound – which builds up an echo picture of the growing foetus-were developed primarily to monitor the baby’s health. Likewise a fetoscope- a special telescope – can be inserted under anaesthetic through the mother’s stomach wall and into the; this can give information about any visible problems, such as a limb deformity.
Recent research has produced a lot of information about how the unborn baby moves, sees, hears. For example, in the early weeks after, the baby is sufficiently well formed to bend his fingers around an object, and in response to a touch on the sole of his foot he curls his toes. It seems that the level of the baby’s activity- kicking and squirming- increases when the mother is under emotional . With prolonged stress, there is an increase in movement up to 10 times the normal level.
Quite early on in pregnancy, the eyes of the foetus move when it changes position or goes to sleqp and in late pregnancy, when some light can penetrate into the womb from outside, the baby’s activity increases in response to a bright light.
After about 20 weeks it seems that the ears are working, as the foetus responds to a wide variety of sounds, including loud outside noises such as a door slamming. Of course, the foetus is surrounded by noise in the womb, such as the rhythmic sound of blood circulation, and of air passing through the mother’s intestine. A mother’s natural tendency to hold a new born baby on the left side, where he can hear her heartbeat, may have a calming effect because it is providing the same reassuring rhythm which he has been used to inside the womb.