Antenatal fetal monitoring can prevent intrauterine fetal death. The primary monitoring is fetal heart monitoring, with reference to timely ultrasound and umbilical artery Doppler flow velocity to assess intrauterine fetal status. Clinical antenatal fetal monitoring techniques include fetal movement, contraction stress test, no stress test, biophysical scoring, and umbilical artery Doppler flow velocity. Maternal-fetal movement assessment Decreased fetal movement signals the onset of intrauterine fetal death, which in some cases occurs within a few days after the decrease in fetal movement. This sign suggests that maternal self-counting of fetal movements (number of fetal kicks) can be used as a means of prenatal fetal monitoring. Although several protocols for counting fetal movements are used in clinical practice, the ideal fetal movement count and fetal movement interval have not been determined. One monitoring method is to count the accurate number of fetal movements in the left lateral position of the pregnant woman, and 10 accurate fetal movements counted in 2 hours is considered as satisfactory fetal movements. The average interval of 10 consecutive fetal movements is 20.9 (±18.1) minutes; another monitoring method is to count fetal movements 3 times a week for 1 hour each time, and it is considered reliable if the number of fetal movements is equal to or exceeds the base number of previous fetal movements counted by the pregnant woman. Therefore, regardless of the method of fetal movement counting, if the exact number of fetal movements cannot be determined, further fetal evaluation is recommended. Contraction stress test is the change in fetal heart rate in the presence of contractions and is based on the theory that contractions cause transient fetal hypoxia. A satisfactory pattern of uterine contractions is at least 3 contractions in 10 minutes, each lasting 40 seconds. If the woman has satisfactory spontaneous contractions, no contractions need to be induced. If the contraction frequency is less than 3 contractions in 10 minutes or lasts less than 40 seconds, contractions can be induced by stimulation of the nipple or intravenous indocin. The results are classified as follows Negative: no late decelerations or significant variable decelerations; Positive: late decelerations after more than 50% of contractions (even if the contraction frequency is less than 3 contractions in 10 minutes); Highly suspicious positive: intermittent late decelerations or significant variable decelerations; Suspicious positive: fetal heart decelerations during every 2 minutes or more frequent contractions or each fetal heart deceleration lasting more than 90 seconds; Unsatisfactory CST : less than 3 contractions in 10 minutes or indeterminate contractions. CST before 37 weeks of gestation is a safe and effective method to monitor fetal heart response. The theory behind the stress-free test is that the fetal heart rate accelerates with fetal movement in the absence of acidosis or neurological stress. Changes in fetal heart rate are a good indication of normal fetal autonomic activity. Reactive disappearance is associated with the fetal sleep cycle in most cases, but may also be caused by central nervous system depression, such as fetal acidosis. The NST is divided into reactive and unresponsive: reactive NST or normal NST is commonly defined as the presence of 2 or more fetal heart accelerations within 20 minutes. Nonreactive NST is defined as no satisfactory fetal heartbeat acceleration for more than 40 minutes. There is a 50% chance that variant decelerations may occur with NST, and if they are not recurrent and last less than 30 seconds, there are no fetal complications or no obstetric intervention is required. Recurrent variable decelerations (3 occurrences in 20 minutes), even if mild, increase the risk of termination of pregnancy by cesarean section. decelerations lasting more than 1 minute in NST significantly increase the risk of cesarean section and intrauterine fetal death. In this case, the decision to terminate the pregnancy is made by considering the potential pros and cons risks. Biophysical score Fetal biophysical score: a four-component observation of the stress-free test combined with a timely ultrasound examination. It includes No Stress Test NST, Fetal Respiratory Movement, Fetal Movement, Fetal Tone, and Amniotic Fluid Depth. Each score is 2 or 0, 8 or 10 is normal, 6 is suspicious, and 4 or less is abnormal. Regardless of the total score, hypohydramnios (amniotic fluid deepest diameter less than ) should be further evaluated. Although hypohydramnios can be based on an amniotic fluid depth of less than 2 cm or an amniotic fluid index of less than 5 cm, data from RCTs support the diagnosis of hypohydramnios with an amniotic fluid depth of less than 2 cm. Umbilical artery flow Doppler flow velocity is used as a non-invasive technique for prenatal monitoring of fetal growth restriction because the umbilical artery flow velocity waveform is different in a normal developing fetus than in a growth restricted fetus. The umbilical artery in a normally developing fetus is characterized by high diastolic flow velocities, whereas the umbilical artery in a growth-restricted fetus has reduced diastolic flow velocities. In some cases of severe fetal growth restriction, the diastolic flow in the umbilical artery is absent or even refluxed. In this case, perinatal mortality is significantly increased. Clinical considerations and management How to ensure the reliability of normal prenatal fetal monitoring results In most cases, normal fetal monitoring results are highly reliable with a low false negative rate. data from RCT show a negative predictive value of 99.8% for NST and 99.9% for CST and BPP. Fetal umbilical artery flow velocimetry is the main monitoring tool for prenatal monitoring of intrauterine growth restriction and has a negative predictive value of 100%. The false-negative rate of these tests depends on the appropriate response during the rapid deterioration of the maternal clinical condition. These monitoring tools cannot predict stillbirth due to rapid changes in maternal-fetal status, such as placental abruption and umbilical cord torsion. In addition, normal antenatal monitoring results are not a substitute for fetal monitoring at delivery. There is no evidence that antenatal fetal monitoring reduces the risk of fetal death or improves perinatal outcomes Evidence on the significance of antenatal fetal monitoring is context-dependent, with evidence deriving mainly from the fact that the results of antenatal fetal monitoring are strongly associated with fetal mortality. There is no high-quality evidence from RCTs that antenatal fetal monitoring reduces the risk of fetal death, but nonetheless, antenatal fetal monitoring is widely used in clinical practice in developed countries. Indications for prenatal fetal monitoring Maternal conditions: 1, diabetes mellitus 2, hypertensive disorders 3, systemic lupus erythematosus 4, chronic kidney disease 5, antiphospholipid antibody syndrome 6, hyperthyroidism (unsatisfactorily controlled) 7, hemoglobinopathy (sickle cell-thalassemia) 8, cyanotic heart disease Pregnancy-related conditions: 1, hypertensive disorders of pregnancy 2, preeclampsia 3, decreased fetal movement 4, gestational diabetes mellitus (unsatisfactorily controlled or medically treated) The timing of starting antenatal fetal monitoring during pregnancy depends on a number of factors, including the prognosis of the newborn after survival, the risk of intrauterine fetal death, the risk of fetal death, and the risk of fetal death. The risk of intrauterine death, the severity of the mother’s illness, and the risk of potential complications for the preterm infant following a medically induced termination of pregnancy due to a false-positive monitoring result. Based on theoretical models and numerous clinical trials, it is recommended that prenatal fetal monitoring be initiated after 32 weeks of gestation, which is also appropriate for most pregnancies. However, for multiple comorbidities, especially in extremely complicated high-risk pregnancies (e.g., chronic hypertension combined with intrauterine growth restriction), prenatal monitoring can be started at the week of gestation when the terminated fetus is viable. Frequency of antenatal fetal monitoring There are no extensive clinical trials to guide the frequency of antenatal fetal monitoring; therefore, the frequency of antenatal fetal monitoring is not definitive and is individualized with clinical judgment. For most fetuses with intrauterine growth restriction, a series of ultrasound examinations every 3-4 weeks is sufficient to adequately assess fetal status; ultrasound examinations performed less frequently than 2 weeks are not recommended because systematic errors in ultrasound can interfere with proper assessment. Further evaluation is required once there is a significant change in maternal-fetal status. What to do in case of abnormal antenatal fetal monitoring Abnormal antenatal fetal monitoring findings should be analyzed in the context of the clinical situation. Acute maternal conditions (e.g., diabetic ketoacidosis or hypoxemia due to pneumonia) can lead to abnormal fetal monitoring results, which will normalize as the maternal condition improves. In this case, correcting the maternal condition and re-monitoring the fetal condition is the best way to handle the situation. Because of the high false positive rate and low positive predictive value of prenatal fetal monitoring, abnormal monitoring results often require further monitoring or consideration of termination of pregnancy in conjunction with gestational age and maternal-fetal condition. Multiple fetal monitoring methods are usually used to achieve a good negative predictive value and to avoid unnecessary termination of pregnancy due to abnormal results of a single monitoring method. The mother complains of decreased fetal movement and should be further evaluated with NST, CST, and BPP; abnormal NST results usually require further CST or BPP; a BPP score of 6 is suspicious positive and requires further evaluation or termination of pregnancy in the context of gestational weeks. A BPP score of 4 is usually an indication for termination of pregnancy, even if the gestational week is less than 32 weeks, management should be individualized and further monitoring is a reasonable option. In most cases, a BPP score of less than 4 is indicated for termination of pregnancy. If no termination is planned (e.g., less than 32 weeks’ gestation), prenatal fetal monitoring is not recommended because the results do not affect management. Does low amniotic fluid affect the decision to deliver? Low amniotic fluid is defined by ultrasound measurements of the deepest pool of amniotic fluid less than 2 cm or an amniotic fluid index less than the RCT indicating that a diagnosis of low amniotic fluid at the depth of the deepest pool of amniotic fluid compared to the amniotic fluid index reduces unnecessary obstetric interventions without increasing adverse perinatal outcomes. The management of hypohydramnios depends on a variety of factors, including gestational age and maternal-fetal status. Experts agree that simple persistent amniotic fluid hypohydramnios (deepest pool of amniotic fluid less than 36-37 weeks of gestation can terminate the pregnancy. In cases of hypohydramnios at less than 36 weeks of gestation with intact membranes, the decision to maintain or terminate the pregnancy is individualized, taking into account the gestational week and maternal-fetal status. If termination is not planned, follow up on amniotic fluid volume, NST and fetal growth. Implications of umbilical artery and other Doppler flow velocity studies In fetuses with intrauterine growth restriction, umbilical artery flow velocity measurements combined with NST and BPP monitoring may improve the prognosis. Other fetal arterial ultrasound monitoring, such as the middle cerebral artery resistance index, can simultaneously assess the status of the fetus with intrauterine growth restriction. However, these flow index measurements have not improved perinatal prognosis, so the clinical significance of these measurements has not been established. Do pregnant women need daily monitoring of fetal movements A number of studies have shown that decreased fetal movements are associated with an increased risk of adverse perinatal outcomes. Although counting fetal movements is an economical and convenient way to monitor fetal status, its effectiveness in preventing stillbirth is uncertain. Even the significance of fetal movement counting in helping to establish regular prenatal fetal monitoring is uncertain. data from RCTs suggest that increasing the frequency of prenatal monitoring does not increase the odds of obstetric intervention. Although daily monitoring of fetal movements is not mandatory for all pregnant women, if a pregnant woman feels a significant decrease in fetal movements herself, she should be advised to actively contact her obstetrician for further fetal monitoring. Conclusions Level of evidence 1. Diagnosis of hypohydramnios by the depth of the deepest pool of amniotic fluid compared with the amniotic fluid index reduces unnecessary obstetric interventions without increasing adverse perinatal outcomes. 2. In fetuses with intrauterine growth restriction, umbilical artery flow velocity measurement combined with NST and BPP monitoring may improve prognosis. Evidence 3. Abnormal NST results usually require further CST or BPP. Evidence 1. For multiple comorbidities, especially in extremely complicated high-risk pregnancies (e.g., chronic hypertension combined with intrauterine growth restriction), prenatal monitoring can be started at the gestational week when the terminated fetus is viable. 2, without obstetric contraindications, pregnant women with abnormal prenatal fetal monitoring can be induced, with close monitoring of fetal heart rate and contractions during delivery. 3.Simple persistent amniotic fluid is too small (the depth of the deepest pool of amniotic fluid is less than 36-37 weeks of gestation can be terminated). In cases of hypohydramnios at less than 36 weeks of gestation with intact membranes, individualize the treatment with the gestational week and maternal-fetal status to decide whether to continue to maintain the pregnancy or terminate it. If termination is not planned, follow up on amniotic fluid volume, NST and fetal growth.