Materno-umbilical ratio of hepatitis B virus (HBV) surface antigen exceeds that of human chorionic gonadotropin in HBV-infected deliveries.

Low levels of HBV surface antigen (HBsAg) are commonly present in umbilical blood from neonates born to chronically infected mothers, but the origin and clinical significance of umbilical antigenemia is not clear. The present study was undertaken to investigate whether the umbilical HBs-antigenemia is linked to a demonstrable level of admixture with maternal blood, as evaluated by the assessment of the maternal-umbilical (M/U) ratio of human chorionic gonadotropin (hCG). The latter has a steep gradient across the placenta and is currently used as the most sensitive maternal marker in foetal sampling procedures. HBsAg and hCG were assayed in 6 paired maternal-umbilical serum samples from Kenya. In 3 cases with umbilical serum testing slightly positive for HBsAg, the M/U ratio of the antigen was around 8,000, or more than ten times the M/U ratio of hCG. In conclusion, the assessment of hCG in umbilical blood does not reveal the origin of umbilical HBsAg, unless the sample is grossly contaminated with maternal blood.