The development of the fetal buds can normally be observed at 6-7 weeks of pregnancy in the case of twins. The fetal heart of a twin baby can be observed at 7-8 weeks of pregnancy, i.e. at this point the presence of a twin pregnancy can be fully detected. For women with regular menstrual cycles of 28-30 days, some women can make a preliminary diagnosis of the fetus by ultrasound at 5-6 weeks from the start of their last menstrual period. For women during pregnancy, the time of early pregnancy reaction is also related to the number of fetuses, the vast majority of women with a single fetus have early pregnancy reaction around 45 days of pregnancy. In the case of twins, due to the rapid rise in HCG levels in the body, the early pregnancy reaction can be seen at around 35 days. In addition, after 50 days of menopause, twins can be visualized through ultrasound, and if there are two gestational sacs and two fetal hearts, the diagnosis of twins can be confirmed. Usually the larger the gestational week, the higher the accuracy of the examination, whether singletons or twins, should be taken seriously. Pregnant women should undergo regular maternity checkups to ensure the normal growth and development of the fetus and to prevent preterm labor and other conditions.