Pregnancy is the process of development and growth of the embryo and fetus in the mother’s body. Fertilization of a mature egg is the beginning of pregnancy, and expulsion of the fetus and its appendages from the mother’s body is the termination of pregnancy. For clinical calculations, the gestation period is usually counted from the first day of the last menstrual period, which is about 280 days (40 weeks). Early pregnancy occurs before the end of the 12th week of pregnancy, mid-term pregnancy occurs between the end of the 13th and 27th week, and late pregnancy occurs at the 28th week and beyond. The process of expulsion of the fetus and its appendages from the mother’s body from the beginning of labor to the end of the 28th week of pregnancy and beyond is called labor. Delivery between the 28th and less than 37th week of pregnancy is called preterm labor; delivery between the 37th and less than 42nd week of pregnancy is called full-term labor; delivery between the 42nd and later weeks of pregnancy is called term labor. 1.Why prenatal checkup? Perinatal period refers to a period of time before, during and after childbirth, and China stipulates that the perinatal period should be from 28 weeks of pregnancy to 1 week after childbirth, and calculates the perinatal mortality rate accordingly. Prenatal checkups serve three main purposes: to assess risk factors; to benefit maternal, fetal and neonatal health; and to facilitate necessary medical and psychiatric treatment and follow-up. If serious fetal malformations are found, the pregnancy can be terminated at the right time to avoid the occurrence of birth defects, so it is very important to carry out correct prenatal checkups. 2.When is the prenatal checkup? Prenatal checkups should start from the diagnosis of early pregnancy, the first checkup without abnormalities, should be checked every 4 weeks during the 20-36 weeks of pregnancy, and once a week since the 36th week of pregnancy, making a total of 9 prenatal checkups. All high-risk pregnant women should increase the number of prenatal checkups as appropriate. Calculation of the expected date of delivery: counting from the first day of the last menstrual period, the month plus 9 or minus 3, and the number of days plus 7 (plus 14 in the lunar calendar). The normal blood pressure of pregnant women should not be more than 140/90mmHg, or not more than 30/15mmHg compared with the basal blood pressure. measuring weight should not increase more than 500g per week, more than those who have more edema or negative edema. 3.How many times is it appropriate to do ultrasound examination during pregnancy? The first ultrasound examination: usually in 6-8 weeks of pregnancy. Mainly observe whether it is intrauterine pregnancy, single or multiple fetuses, whether there is fetal heart, the length of the embryonic bud. It is mainly to provide reference for the documentation. Need to hold urine for abdominal ultrasound examination. Second ultrasound examination: 11-13 weeks, mainly measuring fetal NT value. Third ultrasound examination: 16-19 weeks. Provides ultrasound data for the Down screening test and estimates the risk rate. At this time the report appears to describe the biparietal diameter, head circumference, abdominal circumference, femur length, amniotic fluid depth, fetal position, and placental position. There is no need to hold urine. Fourth ultrasound: 22-24 weeks. It is a time-consuming procedure that detects major malformations of the fetus and examines the intracranial structures, heart structures, stomach blisters, kidneys, bladder, intestinal tubes, and the long bones of the limbs in detail. There is no need to hold your urine. At this gestational week, the fetal structure is more developed and most of the fetal abnormalities can be observed. Too early and the fetus is too small for the sonographer’s observation; too late and if severe fetal abnormalities are found, live birth and termination of pregnancy will pose ethical problems. Fifth ultrasound examination: 28-32 weeks. Some fetal malformations are not detected in mid-pregnancy, but may be recognized as the fetus grows and develops, so this is a secondary screening test for malformations. The amniotic fluid index begins to appear on the report. The amniotic fluid index, fetal weight, and umbilical artery S/D values begin to appear on the report. Sixth ultrasound: 36-38 weeks. Fetal biparietal diameter, head circumference, abdominal circumference, and femur length are measured to estimate fetal weight, and the amniotic fluid index, fetal position, and placental maturity and location are used to inform the clinician’s decision about the mode of delivery. In addition, the cervical canal length (cervical insufficiency) and the thickness of the lower uterine muscle layer (for women with a history of cesarean section) are also measured in the later stages of pregnancy, depending on the individual condition of the pregnant woman. If a pregnant woman develops symptoms of discomfort, such as abdominal pain or vaginal bleeding, additional tests can be performed at any time to monitor the condition of the fetus.