EP21.04: Prediction of early pregnancy viability in pregnancies of uncertain viability on ultrasound

To develop a new prediction model for predicting pregnancy viability in a population of patients with pregnancies of uncertain viability (mean gestational sac diameter <25mm without a visible embryo, or an embryo measuring <7mm without cardiac activity). Providing women with a numerical prediction of viability has been shown to be acceptable and useful in reducing anxiety while they await a follow-up scan, but the model in use was derived before the definition of miscarriage was changed in 2012. This was a prospective observational study of 220 women with pregnancies of uncertain viability. Eleven independent variables (maternal age, BMI, smoking status, gestational age, bleeding status, pain score, gestational sac diameter, yolk sac diameter, Crown–rump length, serum progesterone and bhCG) were analysed in two stages. First, each variable's association with pregnancy viability, then their joint association with pregnancy viability in a multivariate logistic regression. A backwards selection procedure was used in the final model to retain only factors associated with pregnancy viability. Maternal age OR 0.36 (95%CI 0.23-0.57, p < 0.001), gestational age OR 0.38 (95%CI 0.24-0.62, p < 0.001), mean sac diameter OR 1.72 (95%CI 0.93-3.18, p = 0.08), presence of a yolk sac OR 4.53 (95%CI 1.81-11.3, p = 0.001), and serum progesterone OR 2.33 (95%CI 1.60-3.38, p < 0.001) were independently associated with pregnancy viability. The following model was devised to produce a probability score P=ey/(1+ey) where p=probability of a viable pregnancy, e=exponential function (inverse log) and y = 8.488-0.205.age-0.960.gestational age+0.109.sac diameter+1.510 if yolk sac present+0.042.progesterone. We have successfully produced a prediction model for pregnancy viability based on maternal age, gestational age, mean sac diameter, presence of a yolk sac and serum progesterone. This could be integrated into clinical practice in Early Pregnancy Units. A prospective validation study is currently underway.