1. How are the early, middle and late stages of pregnancy divided? The period from the 1st day of the last menstrual period to the 6th day of the 12th week (which is about 3 months of pregnancy) is called early pregnancy; the period from the 13th week of pregnancy to the 6th day of the 27th week of pregnancy (which is about 3 months of pregnancy to 6.5 months of pregnancy) is called middle pregnancy; the period from the 28th week of pregnancy to full term is called late pregnancy. 2.Is ultrasonography suitable for early pregnancy? What can be checked? Ultrasound can be done in early pregnancy, but it is not recommended to do frequent and complicated examinations, because the embryo in early pregnancy is fragile and can withstand the necessary examinations, but recreational ultrasound examinations, such as 3D and 4D examinations, should be avoided. The main tests in early pregnancy include: i. Determining if the pregnancy is intrauterine. An experienced physician will scan not only the uterus to observe the gestational sac in the uterine cavity, but also the adnexal areas on both sides of the uterus to exclude the possibility of ectopic pregnancy and to observe whether there is fluid (bleeding) in the pelvis. Second, the size of the gestational sac will be observed and whether it is viable. Third, observe NT (nuchal translucency layer thickness) at 11-14 weeks to determine if there is any abnormality. NT is normally less than 3 mm. when the fetus has chromosomal abnormality or severe cardiac structural abnormality, it can cause obstruction of fetal lymphatic system reflux, thus causing subcutaneous edema in the fetal neck and causing NT thickening. It is recommended that pregnant women of advanced maternal age, those who have had multiple embryonic stoppages, those who have had abnormal fetuses in the past, those with diabetes, those with chromosomal abnormalities, and those with a history of infection in early pregnancy should have NT screening at 11-14 weeks.