Objective The aim of this study was to reach a publicly applicable marker, using the increasing or decreasing trend of different forms of β-human chorionic gonadotropin (β-hCG) during the first 28 days after molar pregnancy evacuation.

Methods The present retrospective cohort study investigated all of the documents of patients with hydatidiform mole according to their pathological results during their admission and follow-up in the past 10 years (2003–2013). The type of the relationship was determined using locally weighted scatterplot smoothing (Lowess Smoother) and fractional polynomial regression (Fracpoly), and then a model tailored to data processing was used for drawing the receiver operating characteristic curve. During the investigation of gestational trophoblastic neoplasia (GTN) risk factors, the multiple logistic regression method was used to control the confounding variables.

Results Among individuals with high-risk molar pregnancy, 11 (18%) had GTN, and the prevalence of GTN in individuals with low-risk molar pregnancy was 13.4%. The slope of the β-hCG line slightly decreases with a rate of change close to zero in individuals with GTN, but the decrease is not statistically significant (P > 0.05). The receiver operating characteristics curve for serum β-hCG measurement after 21 days of molar pregnancy evacuation showed 83% sensitivity at 89% specificity (area under the curve, 0.9), which indicates that this variable has an optimal performance for discrimination between the GTN cases and patients who had spontaneous disease remission. The mean times of reaching the first negative titer in those without neoplasia and reaching a definitive GTN diagnosis were 8.1 (SD, 2) and 6.2 (SD, 1.5), respectively. The most effective remaining variable in the logistic model was uterine size larger than gestational age (95% confidence interval, 0.99–1.31; odds ratio, 1.14) with a slight increase in the risk and borderline significance (P = 0.07).

Conclusions The serum β-hCG measurement after 21 days of molar pregnancy evacuation and slope of the linear regression line of β-hCG showed to be a good test to discriminate between patients who will get spontaneous disease remission and patients developing GTN.