1. Reduced gestational age

　　It may be a miscalculation of the timing of the last period, resulting in a mismatch between the actual and estimated gestational weeks.

　　2. Non-singleton

　　It could be twins or multiple births, as the value of multiple pregnancies is higher than that of single births.

　　3.Hydatidiform mole

　　It may be an abnormal pregnancy, hydatidiform mole, where the blood HCG value is usually higher than the normal pregnancy value for the corresponding gestational week. If confirmed as hydatidiform mole, immediate hospitalization is required.

　　4. Fetal protection after injection of HCG

　　On the checklist of down's screening, the reference range of the median multiple of screen-hcg is 0-2.5. If the value is higher than that, it will have a negative impact on maternal and child safety during pregnancy, for example, pregnant women are more likely to suffer from preeclampsia, which needs to be judged based on the individual's actual situation. Some pregnant women have been injected with HCG in the early pregnancy to protect the fetus, so there is a possibility that the HCG value is too high when doing tang sifter.