A pregnant woman goes through a number of physical changes, all of which are geared towards delivering a healthy child without harming the mother. Starting from the day of conception to the day of delivery, pregnancy lasts for 266 days or 38 weeks. This duration can be divided into three periods, each lasting three months and are known as the first, second and third trimesters respectively. Each trimester is accompanied by its own unique set of changes to the body. The earliest symptoms can be very subtle and may not be easily noticeable until weeks. However, some women have also talked about sensing pregnancy within hours of conception.