Are you curious how big your developing baby is, what your baby looks like as it grows inside you, and when you'll feel it move? Fertilization happens when a sperm meets and penetrates an egg. It's also called conception. At this moment, the genetic makeup is complete, including the sex of the baby.
Within about three days after conception, the fertilized egg is dividing very fast into many cells. It passes through the fallopian tube into the uterus, where it attaches to the uterine wall. The placenta, which will nourish the baby, also starts to form.
Your baby is considered at 'term' when he is 37 weeks. He is an early term baby if born between 37-39 weeks, at term, if he's 39-40 weeks and late term if he's 41-42 weeks.
A mother's due date marks the end of her 40th week. The delivery date is calculated using the first day of her last period. Based on this, pregnancy can last between 38 and 42 weeks with a full-term delivery happening around 40 weeks.
Some post-term pregnancies -- those lasting more than 42 weeks -- are not really late. The due date may just not be accurate. For safety reasons, most babies are delivered by 42 weeks. Sometimes the doctor may need to induce labor.