Fetal size at 37 weeks of gestation is small by 1 week It is necessary to verify the week of gestation in conjunction with the last menstrual period and early ultrasound to determine whether the pregnancy is full term. Delivery at 28 weeks but less than 37 weeks (196-258 days) is called preterm labor, and fetuses delivered at this time are called preterm infants. The organs of a premature baby are not fully developed, and the lower the birth weight and the smaller the gestational week at birth, the worse the prognosis. At 37 weeks of pregnancy, if menstruation is usually regular, and the early ultrasound verification of gestational week is consistent with the time of menopause, the fetus at 37 weeks of pregnancy will be considered full-term even if it is one week smaller. If menstruation is usually irregular, and the verification of gestational week in early pregnancy is one week smaller than the actual time of menopause, then the 37th week of menopause will need to be counted according to the 36th week of actual pregnancy, which is not considered full-term. Regular checkups are required during pregnancy, and a professional obstetrician will assess the size of the fetus and the gestational week, and deal with any abnormalities in a timely manner.