For the last 5 weeks, I was feeling very constipated, my stomach felt bloated. Before this, I never got the urge to pee in middle of night. Now I understood why this all happened. Morning sickness hasn't started at this stage. Reading on internet, I found out following development has taken place so far.
Week 1 : Not sure, why this is called week 1 of pregnancy as conception might not have happened so far. By the end of perod, the inner lining of uterus thickens in preparation for implantation primarly because of an increase in the progesterone hormone. If the implamantation doesn't take place, the hormone level drops and body gets rid of thickened layer in form of bleeding (period). No sign of baby at this stage, it's still hidden in one of the luck ovaries.
Week 2 : Also known as 1 week before the conception or the magic week.
Body is working hard for the ovulation. Progestrone level is rising and uterus is thickening. Period has come to an end and one of the ovaries is ripening and will soon released. After being released, it will have to make a journey down the fallopian tube in search of the lucky sperm.
Week 3: 1 week after conception
Within hours after lucky sperm meets lucky egg, resulting zygote starts to continuously divide.
Within 6-7 days, it turns into blastocyst(microscopic ball of 100 cells) and it heads on its journey from fallopian tube to its home for 8 1/2 mths,i.e, uterus.
Body starts to produce a hormone called HCG( Human Chorionic Gonadtrophin) which is detected in urine while doing a pregnancy test. It is this hormone which ensures that ovaries are producing more progestrone so that body doesn't get rid of lining of uterus. Ovaries will continue to produce progestrone for about 9 weeks, until the placenta takes over. It's the side effect of this increase in hormone which leads to morning sickness, tender nipples , indigestion and other pregnancy symptoms.
Week 4: Implantation week
To be baby, the blastocyst is now called embryo and has reached uterus where it will stay connected to its mother until delivery. Now it undergoes the great division and splits into 2 groups. First half will become son or daughter while the other half will become the placenta (baby's lifeline). The water bag,i.e amniontic sac, is forming and so is the yolk sac, which later gets incorporated into baby's developing digestive tract. The 3 layers of embryo is getting to grow into specialized parts of the tiny body.
1. Ectoderm - The outer layer will form nervous system, hair, skin, and eyes.
2.Mesoderm - The middle layer will soon be baby's heart, sex organs, bones, kidneys, and muscles.
3. Endoderm - The inner layer will form into digestive system, liver and lungs.
Note: During this period, some women suffer from bleeding, menstrual cramps which is normal as it happens because of the implamantation.
Week 5 : Baby's brain has started to develop. The placenta and umbilical cord has developed and is providing feed to new body. It pumps in oxygen, expels waste and supply essential nutrients. Little one is about the half the size of a grain of rice, around 2 mm long.
Source of reference: What to expect when you're expecting