Background. To investigate the value of a single determination of hyperglycosylated hCG (hCG-H) for predicting the clinical outcome of patients with threatened abortion in the first trimester of pregnancy. Methods. Prospective study performed on 86 consecutively selected women with a diagnosis of threatened abortion and viable intrauterine pregnancy in the first trimester of pregnancy, conducted in two tertiary care hospitals. All patients underwent a single blood sample to determine hCG-H and total hCG serum levels and a transvaginal ultrasound 12-24 hours after diagnosis. Patients were monitored to determine whether the outcome was a miscarriage before the 20th week of pregnancy. Results. Forty-three women (50%) had a miscarriage during the follow-up. We observed a very high correlation between hCG-H and total hCG (r = 0.91, p < 0.001). Median hCG-H and total hCG from pregnancies with normal outcome was significantly higher than those ending in abortion. hCG-H and total hCG were very similar predictors of pregnancy outcomes (AUC: 0.90 and 0.89, respectively). The ratio hCG-H / total hCG was a poor predictor (AUC: 0.64). Conclusion. A single hCG-H assay is helpful for predicting pregnancy outcomes in women with first trimester threatened abortion and viable or potentially viable pregnancy at the time of presentation. However, hCG-H is not a better predictor than total hCG.