Pregnancy is the carrying of one or more offspring, known as a fetus or embryo, inside the womb of a female. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets. Childbirth usually occurs about 38 weeks after conception; i.e., approximately 40 weeks from the last normal menstrual period (LNMP). The World Health Organization defines normal term for delivery as between 37 weeks and 42 weeks.