There are three stages of pregnancy. These are the first, second and third trimesters. The first trimester runs from week one to week fourteen, the second covers weeks 15 – 26, then the third is weeks 27 – 40.
Week 1+2: This is actually before you get pregnant. It’s the stage where your body prepares itself by ovulating. And it’s in these 14 days that the egg is fertilized by the sperm
Week 3: The fertilized egg now moves down the fallopian tubes, fluid passes into the ball of cells, dividing them into two. The inner cells will form your baby and the outer cells will form the placenta. Your body, at this stage, is still unaware that it is pregnant. The implantation begins as the cell ball reaches the wall of the uterus. In this process the cells actually bury into the uterus wall, which can sometimes lead to you having spotting. The implanted cell ball now becomes an embryo.
Week 4: This is a week of rapid development, and your body now realises it is pregnant. The amniotic sac and cavity begin to develop and also the Yoke sac appears (this will later form the baby’s digestive system). The placenta now starts to form where implantation took place and blood from you will now go into the placenta. It is usually about day 27 that we start to feel the morning sickness.
Week 5: The primitive streak (the fore runner of the brain and spinal cord) is now developing. Through this primitive streak the cells will develop into three layers:
The endoderm: the bottom layer – develops the glands, lung linings, tongue, bladder, digestive tract, tonsils, urethra and associated glands.
The mesoderm: the middle layer – forms the muscles, bones, heart, lungs, spleen, blood cells, and the reproductive and excretory systems.
The ectoderm: the top layer – forming the skin, nails, hair, eye lens, nose, mouth, anus, tooth enamel, pituitary gland, mammary glands, and all parts of the nervous system.
Other cells will be starting to develop the spine (called the notochord). The first steps towards forming the embryos head, and the first formation of the babies blood cells happen this week.
Week 6: The first few days of this week is when your baby’s heart starts beating. The aorta (the largest artery in the whole body) will be starting to form at around day 40. By mid week many organs are starting to form: eyes, arm buds, liver, gall bladder, stomach and intestines, lungs and pancreas.
Week 7: This is a busy week for your growing baby. During this week your baby will double in size. The lenses of the eyes are developing and there is also a recognisable tongue. The legs and arms are developing into paddles, the jaws are now visible.
Week 8: The cerebellum starts to form this week. That’s the part of the brain responsible for the movement of muscles. Also hand and foot plates, elbow and wrist areas are forming. Towards the end of the eight week the hand plate has formed ridges where the fingers will be. There is further development of the eye; pigment is now appearing on the retina. Teeth buds are now forming within the gums, along with the wind pipe, bronchi, and voice box. The heart is now starting to develop the four chambers.
Week 9: Your baby is now starting to form cartilage and bones. During this week the ovaries will develop into the sex organ determining whether you’re having a boy or a girl. The fingers and thumbs are now taking shape. Also the baby is now becoming more active.
Week 10: It’s now that your embryo has become a baby, all be it on a rather small scale. There is a fully formed upper lip. The development of the heart now slows as it is past the critical stage. By mid week the earlobes are fully formed. Toes start to develop on the foot plate. As the bones of the palate (roof of the mouth) start to fuse together, the tongue starts to develop taste buds.
Week 11: as the morning sickness starts to subside, you may feel your appetite increase. Your baby’s body starts to straighten. In males the penis is now distinguishable and in females the vagina is beginning to develop. This stage is where the baby starts to show individuality, as the muscle structure varies in each baby.
Week 12: Your baby will start to develop fingernails over the next three weeks. The brain is now the same structure as it will be at birth. By the end of the week, the gall bladder and pancreas will be fully developed. Also the baby will now be opening and closing its mouth.
Week 13: This week vocal chords will form in the larynx. Also the intestines will move from the umbilical cord into the abdomen, and will start to form folds and become lined with villi.
Week 14: You may have noticed some changes to the areola (the area around your nipple); it may be getting larger and darker. Your baby’s heart beat will now be able to be heard using a Doppler. Breathing, sucking and swallowing motions will be being practised. The breathing practises will take the amniotic fluid in and out of the lungs. Baby’s hand also becomes more functional.
Week 15: The baby’s neck is now defined, with the head now resting on the neck rather than the shoulders. The hair pattern of the baby will be defined by the 102nd day of the pregnancy your baby will now be able to turn its head, open its mouth, kick, press its lips together and turn its feet.
Week 16: This week the baby’s toe nails will start to grow. The muscles will be growing stronger and the neck and head are growing straighter. As the uterus starts moving upwards you may start showing more, but this does mean less pressure on your bladder, making you feel like urinating less.
Week 17: Your baby will be working on more reflexes this week; blinking, sucking, and swallowing. Development is carrying on with all the existing structures. Through the course of this month your baby’s weight will increase 6 times.
Week 18: By mid week your baby’s eyes and ears will now be in the right places. The finger tips and toes will develop pads, and toe and finger prints will start to develop later in the week. Myelinization, a process of coating the nerves with a fatty substance called myelin which speeds up nerve cell transmission and insulates nerves, will start happening this week. Also by the second day of this week meconium (faecal waste) will start developing in the baby’s bowels.
Week 19: A creamy looking substance that covers the baby’s body, vernix coseosa, will start to form. This protects the baby and its developing glands and sensory cells. If you’re having a baby girl primitive egg cells are now developed in the ovaries, in fact females are born with all the eggs their ovaries will ever have.
Week 20: Most of the major development has now taken place, and the danger zone of the first three months is now over. Your baby will be waking and sleeping, just as newborns do. Also the formation of fine scalp hair and eyebrows will begin.
Week 21: Your body is replacing the amniotic fluid very three hours at this stage of your pregnancy. Baby’s leg and arm movements increase as the muscles and bones become stronger. By the end of the week a stethoscope will be able to detect the baby’s heart beat.
Week 22: If the baby is a boy, the testes will start to move from the pelvic area into the scrotum. The hair on the head and eyebrows is now visible as white and short.
Week 23: The bones in the middle ear start hardening making the conduction of sound possible. The baby will start to gain some considerable weight between now and next month. The size of the baby’s body will start to get into proportion though the head will remain larger than the rest of the body.
Week 24: The skin of your baby is wrinkled, but will smooth out as fat is deposited. Also by the end of this week the baby’s heart beat is so strong it is some times possible to hear it by placing an ear on your stomach.
Week 25: Baby’s skin is now turning a reddish/pink as capillaries start to develop. The nostrils will now start to open, as they have been plugged unto now. The lungs will start developing blood vessels and the finger and toe nails will now be covering half the nail bed.
Week 26: with the nostrils now open, muscular breathing will start. By the end of the week the lungs will be secreting surfactant, a substance which prevents the lung tissue sticking together. Also with the formation of blood vessels in the lungs, they will now also be developing air sacks. Brain wave activity starts this week for auditory and visual activity.
Week 27: Bumping and thumping is becoming stronger as your baby grows stronger, you should be feeling around 10 kicks in a two hour period. Baby’s lungs are growing rapidly and there is continual development with brain patterns.
Week 28: This is when the eyelids un-fuse and open up. Muscle tone is improving, and the lungs are capable of breathing air. The chances of a baby being born premature from now on, has a greatly improved chance of surviving.
Week 29: Eye lashes have now grown, and although still unable to focus, baby’s eyes are now sensitive to dark and light. At this stage of pregnancy the senses of sound, smell and taste are developing. By the end of the week your baby will be able to move its eyes in their sockets.
Week 30: Baby is now storing up nutrients taken in by you. Calcium for skeletal development, protein for growth and iron for blood cells. By the end of the week the languno (the small hairs that covered the baby’s body), is nearly all gone apart from some patches on the shoulders and back.
Week 31: As the actual growth starts to slow down, the internal organs are still maturing, so make sure your still getting enough folic acid, iron and calcium. Should your baby be born this week they would have the ability to breath, see, listen learn and remember.
Week 32: The baby’s iris is now reacting to light. All five senses are now registering with your baby, although smell is limited as baby can’t breathe air in the uterus.
Week 33: your baby may now be sucking its fingers. Constipation could be starting for you as your uterus puts more and more pressure on your bowels.
Week 34: The pigment of the eyes is not quite fully developed yet, this leaves the eyes looking blue regardless of final colour. And this week your baby will start to develop its own immune system.
Week 35: In baby boys the decent of the testes will complete any time now. Your baby may now shift into your pelvis in a head down position, but not all babies’ do this before birth.
Week 36: Dimples on the elbows and knees will be forming as well as creases in the neck area due to continual deposits of fat. Also this fat will help baby maintain its body temperature.
Week 37: Around 85% are born within two weeks of their actual due date (either before or after), so as you enter this stage be aware for signs of labour. The baby is practising being more aware of its surroundings; this is the ‘orientating response’. This is where the baby will turn towards any source of light. The end of this week marks the end of development, growth will now slow down.
Week 38: Meconium is accumulating in the intestines. Meconium is a dark green mass of waste product and cells from the gall bladder, liver and pancreas. Although shortly after birth this will all come out.
Week 39: as the baby is settling into your pelvis, you maybe feeling clumsy and off balance. This is because your centre of gravity shifts. Make sure you’re prepared for your trip to the hospital.
Week 40: welcome to the final week, that’s if you have not given birth already. Your body will be giving the baby antibodies so it can protect its self from many diseases. The baby will finish dropping into its resting place before birth. So congratulations and welcome to your new born child.