1. Less weeks of pregnancy
The time of the last period may have been misestimated, resulting in a
discrepancy between the actual gestational age and the estimated gestational
2. Non-single fetus
It could be twins or multiple births, as the number of multiple pregnancies
is higher than that of single pregnancies.
It may be an abnormal pregnancy - hydatidiform mole, in which blood HCG
values are usually higher than normal pregnancy values for the corresponding
gestational week. If hydatidiform mole is confirmed, immediate hospitalization
4. Injected WITH HCG to protect the fetus
The median multiple reference range of -HCG on the down's screening list is
0-2.5. If it is higher than that, it will have an adverse impact on the safety
of mother and child during pregnancy, such as the risk of pregnancy-induced
hypertension. Some pregnant women have been injected with HCG in the early stage
of pregnancy to avoid pregnancy, so there is a possibility that the HCG value
may be higher when tang sieving.