There are three stages of pregnancy. These are first, second and third trimesters. The first trimester runs from week one to week fourteen, second covers weeks 15 – 26, then third is weeks 27 – 40.
Week 1+2: This is actually before you get pregnant. It’s stage where your body prepares itself by ovulating. And it’s in these 14 days that egg is fertilized by sperm
Week 3: The fertilized egg now moves down fallopian tubes, fluid passes into ball of cells, dividing them into two. The inner cells will form your baby and outer cells will form placenta. Your body, at this stage, is still unaware that it is pregnant. The implantation begins as cell ball reaches wall of uterus. In this process cells actually bury into 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 Yoke sac appears (this will later form baby’s digestive system). The placenta now starts to form where implantation took place and blood from you will now go into placenta. It is usually about day 27 that we start to feel morning sickness.
Week 5: The primitive streak (the fore runner of brain and spinal cord) is now developing. Through this primitive streak cells will develop into three layers:
The endoderm: bottom layer – develops glands, lung linings, tongue, bladder, digestive tract, tonsils, urethra and associated glands.
The mesoderm: middle layer – forms muscles, bones, heart, lungs, spleen, blood cells, and reproductive and excretory systems.
The ectoderm: top layer – forming skin, nails, hair, eye lens, nose, mouth, anus, tooth enamel, pituitary gland, mammary glands, and all parts of nervous system.
Other cells will be starting to develop spine (called notochord). The first steps towards forming embryos head, and first formation of 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 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 eyes are developing and there is also a recognisable tongue. The legs and arms are developing into paddles, jaws are now visible.
Week 8: The cerebellum starts to form this week. That’s part of brain responsible for movement of muscles. Also hand and foot plates, elbow and wrist areas are forming. Towards end of eight week hand plate has formed ridges where fingers will be. There is further development of eye; pigment is now appearing on retina. Teeth buds are now forming within gums, along with wind pipe, bronchi, and voice box. The heart is now starting to develop four chambers.
Week 9: Your baby is now starting to form cartilage and bones. During this week ovaries will develop into sex organ determining whether you’re having a boy or a girl. The fingers and thumbs are now taking shape. Also 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 heart now slows as it is past critical stage. By mid week earlobes are fully formed. Toes start to develop on foot plate. As bones of palate (roof of mouth) start to fuse together, tongue starts to develop taste buds.
Week 11: as morning sickness starts to subside, you may feel your appetite increase. Your baby’s body starts to straighten. In males penis is now distinguishable and in females vagina is beginning to develop. This stage is where baby starts to show individuality, as muscle structure varies in each baby.
Week 12: Your baby will start to develop fingernails over next three weeks. The brain is now same structure as it will be at birth. By end of week, gall bladder and pancreas will be fully developed. Also baby will now be opening and closing its mouth.
Week 13: This week vocal chords will form in larynx. Also intestines will move from umbilical cord into abdomen, and will start to form folds and become lined with villi.
Week 14: You may have noticed some changes to 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 amniotic fluid in and out of lungs. Baby’s hand also becomes more functional.
Week 15: The baby’s neck is now defined, with head now resting on neck rather than shoulders. The hair pattern of baby will be defined by 102nd day of 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 baby’s toe nails will start to grow. The muscles will be growing stronger and neck and head are growing straighter. As 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 existing structures. Through 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 right places. The finger tips and toes will develop pads, and toe and finger prints will start to develop later in week. Myelinization, a process of coating nerves with a fatty substance called myelin which speeds up nerve cell transmission and insulates nerves, will start happening this week. Also by second day of this week meconium (faecal waste) will start developing in baby’s bowels.