Objective The aim of this study was to develop a serum human chorionic gonadotropin (hCG) normogram for both uneventful complete and partial hydatidiform moles in the first-trimester ultrasound era.

Methods An hCG normogram for both complete and partial hydatidiform moles was constructed, based on 639 patients with uneventful serum hCG regression after evacuation between 1990 and 2014. Serum hCG was measured by an in-house–developed radioimmunoassay, detecting both intact hCG and free β-subunit. It has been in use for all serum measurements sent to the Dutch Central Registry for Hydatidiform Moles since 1977.

Results Since introduction of routine first-trimester ultrasonography, lower pre-evacuation and follow-up serum hCG concentrations were observed. When compared with complete hydatidiform moles, patients with a partial hydatidiform mole had significantly lower pre-evacuation serum hCG concentration (median, 4400 and 875 ng/mL, respectively; P < 0.001) and earlier hCG normalization (median, 7 and 6 weeks, respectively; P < 0.001) but higher gestational age (mean, 11.5 and 13.0 weeks, respectively; P < 0.001). For both complete and partial hydatidiform moles, 95% of patients reached normal serum hCG concentrations within 14 weeks after evacuation.

Conclusions A normogram for the detection of gestational trophoblastic neoplasia was developed for complete and partial hydatidiform moles. Although interesting from a scientific perspective, the small divergence in hCG regression between complete and partial hydatidiform moles will be of little importance in clinical practice, as actual differences in regression will encompass only days. To promote clarity and unity in daily practice, we therefore propose a combined normogram to be used as a reference guideline for follow-up after evacuation of a hydatidiform mole. This normogram will be compliant with patients in today’s clinical practice.