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.