How long does a human pregnancy last? How does the embryo develop inside the mother's womb? We will explain how to keep track of your pregnancy week by week and month by month, twin pregnancy, the development of the baby from the first cell, etc. Check out our pregnancy, ovulation and fertile days calculators, estimated delivery date, ideal weight and body mass index (BMI). And if you like ultrasound scans, we can show you different scans covering all stages of pregnancy.