“He who sees things grow from the beginning will have the finest view of them” Aristotle 384-322 BC
From the chaotic stampede of sperm towards the gently rolling ovum, to the amazing growth, development and birth of a tiny, yet perfect human, we indeed witness an awesome miracle. Life begins as union of chance and emerges as a masterpiece.
Pregnancy is usually referred to by midwives and doctors as the number of weeks following the last menstrual period. This is not, however, exactly accurate. For the first two weeks after a woman’s last menstrual period pregnancy does not actually occur, rather the ovum (maternal egg) is maturing and getting ready to be released. For this reason I will refer to the baby’s development as weeks from fertilisation, with the weeks of pregnancy that are more familiar to women in brackets.
Pregnancy begins when an ovum released from a prospective mother’s ovary is fertilised by one of the 500 million sperm that approach it. This occurs approximately 14 days after the last menstrual period. Because menstrual cycles can differ in length this varies from woman to woman. The moment the first successful sperm penetrates the wall of the ovum the chemical composition changes, shutting out all other sperm. The winning sperm, once inside the ovum, drops off the tail that has helped sustain and mobilise it during its long and arduous journey. The sperm then releases all the genetic material that will determine the sex and many other characteristics of the unborn baby. Twelve hours after the initial fusion of ovum and sperm the first cell division occurs. This division of cells then re occurs every 12 to 15 hours. Four days after fertilisation the tiny group of cells now known as a blastocyte leave the fallopian tube and enter the mother’s uterus. Here they attempt a tricky ‘lunar landing,’ usually on the upper part of the uterus. Eight days after fertilisation this tiny clump of cells begins to implant into the surface of the uterus. Hormones are released which will signal the body not to menstruate. Women may already begin to feel ‘different’ even though their periods are a week away. Three weeks after fertilisation (5 weeks of pregnancy) when the baby is barely 2mm long, the heart begins beating. The clump of cells is now called an embryo. Four weeks after fertilisation (6 weeks of pregnancy) the basic human design can be seen. Whilst at first impressions it may look vaguely like a sea horse, the baby at only 5-6 mm long already possess the beginnings of a brain, back bone and heart.
The fourth to eight week after fertilisation (6 to 10 weeks of pregnancy) is a crucial period in the baby’s development. All the major internal and external body structures form during this time. Five weeks following fertilisation (7 weeks of pregnancy) the baby will be about 1cm long. Eight weeks following fertilisation (10 weeks of pregnancy) they will be around 4cm in length. Because of the curled up nature of a developing baby all the measurements given will be from the crown of the head to the bottom, or otherwise termed as the ‘sitting height’. The period between four and eight weeks following fertilisation (6 to 10 weeks of pregnancy) is particularly crucial as exposure to factors like certain medications or viruses can lead to malformations. Eight weeks following fertilisation (10 weeks of pregnancy) everything found in a fully-grown human has been formed. The baby looks remarkably human with arms, legs, fingers and toes. The head of the baby will almost be half the size of the entire baby. At this stage the eyes will be open but shortly the eyelids will fuse and not reopen for several months. It would be hard to tell the sex of the baby at this stage, as the genitalia have not differentiated enough. All the baby’s organs are now in place but there is still a great deal left to happen. The risk of malformations and miscarriages now diminishes significantly.
From eight weeks after fertilisation (10 weeks of pregnancy) until birth the baby will be called a fetus. Twelve weeks following fertilisation (14 weeks of pregnancy) the baby will weigh around 45gms and be around 8cm long. They float comfortably in a pool of warm liquor that is around 37.5 degrees, a little higher than the mother’s body temperature. The baby can already hiccup and move around, flexing its little limbs and exploring its new world. Whist the period from 3 to 8 weeks after fertilisation is about the development of body structures, the weeks following this are about rapid growth and differentiation of all these new tissues and organs. Ten weeks following fertilisation (12 weeks of pregnancy) the mother’s uterus will have reached the top of her pubic bone and the heart rate can possibly be heard by the midwife or doctor looking after her. The placenta is now producing all the hormones needed during pregnancy. The most striking thing in this period is the slowing down in the growth of the baby’s head relative to the rest of the body. Twelve weeks after fertilisation (14 weeks of pregnancy) the sex of the baby will now be distinguishable. The baby’s face will have a very distinct human profile and a well-defined neck. By the end of the twelfth week following fertilisation the baby’s arms will have almost reached their relative length to their bodies. The legs are still not so well defined and are proportionally slightly shorter than they will be in relation to the rest of body. Early fingernail development can be seen. The baby will now be forming and excreting urine into the amniotic fluid. Swallowing will also be present. Reflexes will be seen and the baby will react to stimuli.
Between twelve and sixteen weeks following fertilisation (14-18 weeks of pregnancy) the baby grows very rapidly. Sixteen weeks following fertilisation (18 weeks of pregnancy) the baby will weigh around 200gms and be approximately 14cm. The body continues to grow more rapidly than the head and will seem much more in proportion. The legs will have also lengthened and the fetus begins to look like a real baby. The skeleton begins to harden and the eyes, which were more to the side of the head, will be facing forwards. The ears now stand out from the head. If the baby is girl her ovaries will have developed and some early follicles containing ovum will be forming. The baby will become increasingly active, turning its head, moving its face, opening and shutting its mouth and even breathing under water!
Twenty weeks after fertilisation (22 weeks of pregnancy) the baby is about 19cm long and weighs about 460gms. The mother’s uterus will be just level with or above their navel and she will be finding it hard to do up her jeans. The baby can now partly defend itself against infection with its developing immune system. Head hair begins to appear around 20 weeks following fertilisation (22 weeks of pregnancy) and fine hairs called lanugo will cover the body. A greasy protective material known as vernix covers the skin. This will help protect it from damage. The baby develops a special kind of fat called ‘brown fat’ that helps to produce heat and this will be particularly useful when the baby is born. If the baby is a boy the testes will have already begun to descend. Little girls will have now formed the 5 million ova they will have throughout their lives. This is a particularly magical period for the mother as she will begin to feel her baby move. The first movements are called ‘quickening’ and they usually feel like bubbles or flutters in the uterus. Whilst the baby will have been moving for several weeks it takes longer for the moments to be felt through the abdominal wall. First time mothers will generally feel the baby’s movements a couple of weeks later (18-22 weeks) than mothers having subsequent babies (16-18 weeks). The baby now reacts to light and sound so the incredibly noisy world of rumbling tummies and pumping blood can be heard. This is when singing and talking to the baby can be fun. Newborn babies tend to turn more to female than male voices when born, indicating they become quite used to the tones of their mother. At 18 weeks following fertilisation (20 weeks of pregnancy) the law in Australia recognises babies as having certain rights. If a baby were to be born at any time following 20 weeks then the birth would have to be reported and registered.
Twenty-four weeks following fertilisation (26 weeks of pregnancy) the baby will be around 23cm long and weigh around 820gms. Fingernails will now be present and eyes and eyelashes are usually recognisable. The baby gains a lot of weight during these four weeks and they are increasingly better proportioned, though still quite lean. The translucent skin is very pink and even may seem red due to the visible blood in the capillaries. The respiratory system in the baby has now reached a very significant stage that gives it a chance of living if born prematurely. Special cells in the lungs begin to secrete a substance called surfactant that helps to keep the lungs patent and able to absorb oxygen. Currently in Australia babies born 22 weeks following fertilisation (24 weeks of pregnancy) have around a 50% chance of survival and most will be given intensive care treatment. The chance of survival increases with each subsequent week of pregnancy.
Twenty-eight weeks after fertilisation (30 week of pregnancy) the baby is around 27cm and weighs around 1300gms. The chances of the baby surviving if it is born now are around 90%. Their lungs are much more prepared to breath air and the central nervous system has now matured to a stage where it can maintain more rhythmic breathing and control body temperature. The eyes re-open at the beginning of this period and it seems that the fetus probably sees light as a red shimmer. The baby may now have a good head of hair. The skin will not be as wrinkled as ‘white fat’ is being laid down, smoothing the wrinkles out. Toenails also now become more visible.
Thirty-two weeks following fertilisation (34 weeks of pregnancy) the baby weighs around 2100gms and is about 30cm long. The chances of a baby surviving if they are born now are very good. The lungs are much more mature and able to cope with life outside the uterus. The baby’s fingernails have now reached their fingertips and the toenails are better developed. The skin colour is pink and the skin has further smoothed out its wrinkles. The limbs are now getting chubby as the ‘white fat’ keeps increasing.
Thirty-six weeks following fertilisation (38 weeks of pregnancy) the baby will be around 34cm long and around 3000-3500gms. The body should be plump. The fine hairs that have covered the skin for so many weeks now disappear. The toenails now reach the tips of the toes. The baby will tend to flex its limbs and have a firm grasp if you put a finger in its hand. The baby’s abdomen has now reached the same circumference as the head. From now on the baby fattens up and its abdominal circumference will be bigger than the head. During the last couple of months the baby puts on around 200gm a week. The baby’s head may start to descend into the pelvis during this time causing increased pressure on the mother’s bladder and back. As the baby grows the mother may start to feel increasingly tired and find it hard to sleep well at night. Everything inside that cosy, watery world is getting very cramped. From now on (38 weeks of pregnancy) the baby is classified as ‘full term’ and is likely to be born at any time. The baby will be around 33 cm long from the head to bottom or about 50cm long from head to heel. The weight will vary greatly but averages around 3500gms. Approximately only 3% of babies are born on the actual date they are due, which will be around 266 days after fertilisation or 280 days after the first day of the last menstrual period. The skin of the baby is now much whiter or a bluish pink. The white vernix, which was covering the skin, has now mostly come off and it makes the amniotic fluid appear like it has white flecks in it. The chest is more prominent and the breasts have more tissue making them protrude slightly in both sexes. The testes should now be in the scrotum in males. The fingernails will extend beyond the tips of their fingers. There should be plenty of creases on the hands and feet and more cartilage in the ears.
As the nine-month miracle emerges from its shadowy, watery world and greets its parents, that first cry opens up 25 million air sacs in the lungs that up until now have been filled with fluid. As the lungs empty of fluid and fill with air, blood is also re-directed into the lungs and then all over the body. A new life is born. For the parents a roller coaster of emotions and experiences has ended and another called parenthood is about to begin.
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