Occult abnormal pregnancies after first post-embryo transfer serum beta-human chorionic gonadotropin levels of 1.0-5.0 mIU/mL

The majority of negative first post-ET serum β-hCG levels are <1.0 mIU/mL. Results from 1.0 to 5.0 mIU/mL may fail to exclude abnormal pregnancy and are associated with poor outcomes compared with β-hCG levels <1.0 mIU/mL. Serial serum β-hCG may be warranted in this population.