Yolk sac size & shape as predictors of first trimester pregnancy outcome: A prospective observational study

To determine the value of yolk sac size and shape for prediction of pregnancy outcome in the first trimester.

500 pregnant women between 6⁺⁰ and 9⁺⁶ weeks of gestation underwent transvaginal ultrasound and yolk sac diameter (YSD), gestational sac diameter (GSD) were measured, presence/absence of yolk sac (YS) and shape of the yolk sac were noted. Follow up ultrasound was done to confirm fetal well-being between 11⁺⁰ and 12⁺⁶ weeks and was the cutoff point of success of pregnancy.

Out of 500 cases, 8 were lost to follow up, YS was absent in 14, of which 8 were anembryonic pregnancies. Thus, 478 out of 492 followed up cases were analyzed for YS shape and size and association with the pregnancy outcome. In our study, abnormal yolk sac shape had a sensitivity and specificity (87.06% & 86.5% respectively, positive predictive value (PPV) of 58.2%, negative predictive value (NPV) of 96.8% in predicting a poor pregnancy outcome as compared to yolk sac diameter (sensitivity and specificity 62.3% & 64.1% respectively and PPV and NPV of 27.3% and 88.7% respectively). The degree of association for both the variables was significant to the level of p<0.000.

The presence or absence of yolk sac has a strong predictive value for poor pregnancy outcome. Yolk sac shape was a better predictor of poor pregnancy outcome in terms of higher specificity and negative predictive value as compared to yolk sac diameter.