It is important to clarify the concept that the current way of describing the gestational week applied by obstetricians and gynecologists is calculated from the first day of the patient’s last normal menstrual period, 35 days after menopause which means 5 weeks of pregnancy. In early pregnancy it is the last menstrual period that is used to estimate the gestational age and week and the expected date of delivery, however, because some patients do not have regular menstrual cycles, they need to be confirmed or corrected by ultrasound in early pregnancy. In particular, measuring the size of the fetus at 11-14 weeks of gestation to estimate the gestational age is a more accurate method and is not clearly related to when the pregnant woman had sex.