For about the first 12 weeks, the baby’s cells expand and form white blood cells and other cells that are good at destroying bacteria. The placenta helps maintain this by absorbing as much waste as possible.
At around 12 weeks of pregnancy, the placenta will start to break down and make another type of healthy cell. The mother will start to bleed, which means the baby is getting less oxygen.
At around 25 weeks, most cells from the embryo are still in the placenta. You can therefore use this time to catch up on nutrients, but it is safe to say that the baby is now dependent on the mother for everything from nutrition to breathing.
This is also when the baby’s lungs first need to develop. The bigger the placenta, the bigger the lungs – so the longer a woman is carrying the baby, the more “smaller” the lungs.
Pregnancy is generally 12 to 15 weeks long, but there are extreme cases where pregnancy can last for longer than 24 weeks. In these cases, a doctor will refer the woman for an induced abortion, usually due to a genetic condition.
Today, many women choose to extend their pregnancies by taking drugs to stimulate labour. But a new theory which has been extensively tested in China suggests that this might not be necessary.