Yolk Sac Diameter as a Predictor of Pregnancy Outcome: A Prospective Observational study at KLES Dr. Prabhakar Kore Charitable Hospital and MRC, Belagavi

Abstract

Background and Objectives : The secondary yolk sac is the first extraembryonic structure which can be detected with transvaginal sonography (TVS) in the chorionic cavity. It can be seen from the 5th to the 12th week of menstrual age. Yolk sac is the primary source of exchange between the embryo and the mother during organogenesis and before placental circulation is established. It has nutritive, endocrine, metabolic, immunologic, secretory, excretory and hematopoietic functions. This study was conducted to evaluate the secondary yolk sac diameter as a predictor of pregnancy outcome. Methods : In this study the data was collected from the ultrasound records of the women who were evaluated for yolk sac diameter by transvaginal sonography between 6 to 10 week 6 days of period of gestation & who were fulfilling eligible selection criteria. Total 254 women were evaluated. The yolk sac diameter was measured by placing electronic callipers at inner margins. The range of normal yolk sac diameter was considered to be 3-5 mm. While the yolk sac diameter of > 5 mm & < 3 mm were considered as abnormal. Thus two groups were made with normal & abnormal yolk sac diameter. The cases falling in these two groups were followed up to 24 wks of gestation and considered as normal pregnancy outcome if pregnancy continues beyond 24 wks with no foetal anomaly and abnormal outcome if they have spontaneous abortion, missed abortion,threatened abortion ,incomplete abortion, complete abortion, demonstrable foetal anomalies or spontaneous preterm birth. Results : There was a significant correlation between yolk sac diameter and the pregnancy outcome (P= 0.0001). A normal range of yolk sac diameter was considered as 3-5 mm & yolk sac diameter of >5mm & <3mm were considered as abnormal. Using these criteria of yolk sac diameter to predict pregnancy outcome, sensitivity was 50 %, specificity was 83.64 %, positive predictive value was 32.08 % and negative predictive value was 91.54 %. It was also noted that sensitivity, positive predictive value and negative predictive value were highest when the scan was performed at 8th week of gestation and specificity was highest at 9th week of gestation. . The Sensitivity & PPV were very poor at 7th week of gestation. Interpretation & Conclusion : We can conclude from the present study that measurement of the secondary yolk sac diameter between 6th to 10th week 6 days of gestation can be used as a valuable tool to predict pregnancy outcome, even before the detection of the embryo. So that it will help in counseling the patient regarding the risk of miscarriage and the need for follow up ultrasound examinations.