BACKGROUND: Singleton normal fetus with partial hydatidiform mole (PHM) pregnancy is a rare phenomenon. No previous reports have investigated the risk factors of gestational trophoblastic neoplasia (GTN) progression following this condition.
METHODS: We retrospectively enrolled cases of singleton normal fetuses with PHM pregnancies at West China Second University Hospital, Sichuan University, from 2005 to 2017. Other cases were identified from PubMed databases during 1975 to 2021 for the cohort study. Cox proportional hazards models were applied to evaluate risk factors for GTN progression based on the patient\'s clinical characteristics.
RESULTS: Overall, 36 cases of singleton normal fetuses with PHM pregnancies were enrolled. After a median follow-up of 4.0 (0.8-12.0) months, nine (25.0%) patients progressed to GTN. Gestational age at pregnancy termination (hazard ratio [HR] 0.88; 95% confidence interval [CI] 0.78-0.99, p = 0.032), hyperthyroidism (HR 5.75; 95% CI, 1.16-28.50, p = 0.032), and reasons for pregnancy termination (medical indications vs. patients\' choice; HR 0.25; 95% CI, 0.06-0.99, p = 0.049) were significantly correlated with GTN progression. Area under the receiver operating characteristic curve (AUC) of gestational age at pregnancy termination to predict non-progression to GTN was 0.784 (95% CI, 0.615-0.903, p < 0.001). A clinically significant cutoff value, that is, gestational age of 24 weeks, was determined by comprehensively considering the cutoff values of AUC and clinical significance of gestational age.
CONCLUSIONS: Compared to gestational age of pregnancy termination <24 weeks, ≥24 weeks was a protective factor for GTN. Therefore, there is enough evidence to continue pregnancy, except for uncontrolled severe complications, without increasing the risk of GTN progression.

Partial hydatiform mole (MHP) represents a spectrum of trophoblastic-related disorders occurring during pregnancy. Also known as embryonal mole, it is characterized by a recognizable ovum abnormality with vesicular transformation of villi but with recognizable placental appearance and amniotic cavity containing the fetus. First-trimester spontaneous abortion most commonly suggests the diagnosis. Partial moles rarely persist beyond the first trimester and are then a cause of maternal and fetal complications and diagnostic confusion. MHP of genetic origin is triploid with extra chromosome of paternal origin. The coexistence of normal fetal karyotype and MHP is exceptional. We report a rare case of partial molar pregnancy with liveborn diploid fetus in a 36-year-old woman diagnosed with threat of premature labour associated with placenta previa at 27 weeks of amenorrhea (WA).