Fourfold Improved Odds of a Good First Trimester Outcome Once a Yolk Sac Is Seen in Early Pregnancy

To compare first trimester prognosis when an early pregnancy sonogram demonstrates a gestational sac with yolk sac versus gestational sac without yolk sac.

Our study comprised 823 transvaginal sonograms without identifiable embryo performed at least 35 days from last menstrual period (LMP), in which mean sac diameter was <16 mm and first trimester outcome (live or early pregnancy loss) was known. We recorded the presence or absence of yolk sac, first trimester outcome, and several clinical features: maternal age, time since LMP, and presence or absence of vaginal bleeding. We compared the likelihood of a successful first trimester outcome in cases with a visible yolk sac to those without a yolk sac.

At the end of the first trimester, 113 of 270 (41.9%) cases without a yolk sac and 414 of 553 (74.9%) with a yolk sac were live (P < .000001, chi-square). This corresponds to an odds ratio of 4.14 for the presence of yolk sac, a result confirmed by logistic regression. Advanced maternal age, ≥42 days since LMP, and vaginal bleeding all carried an increased risk of loss (P < .000001, chi-square). Outcome was better with a visualized yolk sac than without a yolk sac, regardless of number of risk factors (P < .001, chi-square).

The odds of successful first trimester outcome are 4-fold higher when a yolk sac is seen on an early pregnancy sonogram than when no yolk sac is seen. For any level of risk, based on maternal age, vaginal bleeding, and time since LMP, outcome is significantly better when a yolk sac is seen.