The value of the secondary yolk sac in predicting pregnancy outcome.

One hundred and five consecutive women had transvaginal sonography (TVS) at less than 12 weeks gestation to establish the normal size and shape of the secondary yolk sac (YS) and to assess the YS measurements in predicting pregnancy outcome in the first trimester. A yolk sac diameter more or less than two standard deviation (2SD) from the mean predicted abnormal pregnancy outcome with a sensitivity of 91.4%, specificity of 66% and a positive predictive value of 88.8%. A normal YS size predicted normal pregnancy outcome with a sensitivity of 66%, specificity of 91.4% and a positive predictive value of 95.6%. It is recommended that patients at risk of poor pregnancy outcome should have routine TVS before 12 weeks gestation to assess their YS and those with an abnormal yolk sac should be followed-up closely to exclude fetal abnormalities before 24 weeks gestation.