Complex sentence: The total gestation period from fertilization to birth is about 38 weeks (birth usually occurring 40 weeks after the last menstrual period) and the process of giving birth starts with a series of involuntary contractions of the muscular walls of uterus.
Split into simpler sentences: The total gestation period from fertilization to birth is about 38 weeks (birth usually occurring 40 weeks after the last menstrual period). The normal process of giving birth starts with a series of involuntary contractions of the muscular walls of uterus.