Background: The purpose of this prospective clinical study was to determine and evaluate the prognostic value of secondary yolk sac diameter of the embryo on pregnancy outcome.
Methods: One hundred and thirty pregnant women in the first trimester were included in the study. Crown-rump length (CRL) and yolk sac diameters were measured in every patient and the outcome of the pregnancies were compared with the measurements. Intact normal pregnancy (group A), threatened abortion (group B) and missed abortion (group C) were diagnosed in 67, 43 and 20 pregnancies, respectively.
Results: We detected a significant linear correlation between secondary yolk sac diameter and gestational age in group A (r = 0.5085; p < 0.0001) and a moderate correlation in group B (r = 0.4048; p = 0.007) and C patients (r = 0.3478; p = 0.1333). When the groups were evaluated irrespective of gestational age, a significant difference in secondary yolk sac diameters among the groups was noted (p = 0.037). When confidence intervals for secondary yolk sac diameters of intact normal pregnancies (group A) were calculated by linear regression, two patients in group B were below the 5% confidence interval. However, in group C patients, the yolk sac diameter of six patients were detected below the 5% confidence interval, while two of the measurements were above 95% confidence interval. Therefore, eight measurements (40%) of group C patients were outside the 5-95% confidence interval.
Conclusion: In the first trimester, when discrepancy is detected between secondary yolk sac diameter and gestational age, additional sonographic investigation should be performed one or two weeks later, in order to estimate the pregnancy outcome.