When does the pregnancy count?

Pregnancy days are calculated from the first day of the last menstrual period, not from the time of cohabitation. If menstruation is regular, 28 to 30 days of menstrual cycle, each month will come on time, pregnancy is calculated from the first day of the last menstrual period. If menstruation is irregular, one or two months to menstruation, this situation our doctor will calculate according to the time of cohabitation, or according to the size of the early color ultrasound baby to calculate the last menstrual period, calculate the expected date of delivery. It is suggested that early pregnancy can not smoke, can not drink, can not contact toxic substances, can not contact radiation, can not take drugs casually.