Some of the examinations have clear time limits, so early or wrong results may lead to inaccurate results, or abnormalities may not be detected in time. Early pregnancy examination: usually at least one ultrasound examination is performed before the 13th week of pregnancy to determine whether the pregnancy is intrauterine and to exclude ectopic pregnancy and embryonic dysplasia, so as to prevent the pregnant woman from critical situations. Mid-pregnancy checkups: 1. NT test: NT test is performed at 11-13 weeks + 6 days to determine the risk of chromosomal abnormalities, congenital diseases and malformations of the fetus through NT value, which cannot be advanced or postponed; 2. Down’s screening: Down’s screening is performed at 11-13 weeks + 6 days in early pregnancy and at 16-20 weeks in mid-pregnancy to screen for chromosomal abnormalities such as Down’s syndrome 3. Ultrasound: midterm teratology examination is required at 20-24 weeks of gestation, mainly to screen for fetal structural abnormalities. Third, late pregnancy examination: 1, fetal heart monitoring: after 36 weeks, pregnant women need to carry out weekly fetal heart monitoring, in order to timely detection of fetal abnormalities, ready to deal with, at this time, if you can not timely to the hospital to monitor the fetal heart, may ignore fetal abnormalities; 2, color ultrasound evaluation: 28-32 weeks of pregnancy, 36-37 weeks, also need to carry out color ultrasound evaluation. Maternity checkups are necessary for pregnant women to detect problems with the fetus in a timely manner. For pregnant women with primary diseases or those with high risks, they can control the primary diseases through maternity checkups and monitor them in a timely manner to ensure the health of the pregnancy.