To understand the function of the placenta can be from the following aspects: 1, ultrasound to see the maturity of the placenta, after 38 weeks of gestation placenta maturity level 3, suggesting that the placenta is mature and tends to aging. If the ultrasound before 38 weeks of gestation indicates placental maturity level 3 and S/D ratio > 3, it indicates that the placenta is not well supplied with blood and oxygen and should be further monitored. 2, combined with fetal movement, fetal movement is the best way for pregnant women to monitor themselves. If the fetal movement is abnormal, continuous electronic fetal heart monitoring can be performed in time for early detection and timely diagnosis of intrauterine distress.3. Urinary estriol values and human placental lactogen values in maternal serum can also assess the function of the placental unit, which is rarely used in clinical practice.