Pregnancy is a period which starts with conception and ends with birth. After the egg is fertilized by a sperm and then gets implanted in the lining of the uterus, the egg develops into the placenta and embryo, and later into a fetus, a pregnancy usually lasts 40 weeks, which begins from the starting day of the woman’s last menstrual period. Pregnancy period is divided into three trimesters, each lasts for three months.