Objectives: This study aimed to determine the frequency of a persistent yolk sac in pregnancies at 12 to 13 weeks and to investigate whether a persistent yolk sac is associated with an adverse gestational outcome.
Methods: This study reviewed a total of 282 women who had normal singleton pregnancies with a gestational age of 12 weeks to 13 weeks 6 days and who were consecutively admitted to the study center for first-trimester screening (for chromosomal abnormalities) between April 2010 and February 2011. A persistent yolk sac has been defined as a yolk sac that has achieved a diameter of 5.6 mm or greater without losing its internal pressure at the 12th week of pregnancy or later.
Results: A persistent yolk sac was detected by sonography in 25 pregnancies. The average diameter of the persistent yolk sacs ± SD was 6.3 ± 0.2 mm (range, 5.6-8.0 mm). The frequency of a persistent yolk sac in pregnancies at 12 weeks was significantly higher than that at 13 weeks (P = .017). A persistent yolk sac was not associated with adverse perinatal outcomes, including abnormal sonographic findings, isolated structural defects, poor obstetric outcomes, and perinatal mortality.
Conclusions: Although yolk sacs mostly disappear toward the end of the first gestational trimester, they may sometimes persist even to the 13th week of gestation. The persistence of the yolk sac seems to be unrelated to an adverse perinatal outcome.