Negative urine pregnancy test in a molar pregnancy: is it possible?

A urine pregnancy test is commonly used to detect pregnancy and is based on finding intact β-human chorionic gonadotrophin (hCG) molecules in the urine by an immunoassay system. However, the significantly large amount of β-hCG in molar pregnancy may paradoxically lead to a false-negative result due to a phenomenon known as the 'high dose hook effect'. A case of molar pregnancy with negative urine pregnancy test but very high serum β-hCG is reported. Every obstetrician should be aware of this limitation in the presence of a high index of suspicion of gestational trophoblastic disease but negative urine pregnancy test.