Number of yolk sacs does not predict amnionicity in early first-trimester monochorionic multiple gestations.
OBJECTIVE
To determine the relationship between amnionicity and number of yolk sacs before 11 weeks of gestation.


METHODS
Twenty-two cases of monochorionic multiple pregnancy were scanned before 11 weeks of gestation. There were 21 sets of twins and one of triplets. Amnionicity was determined by visualization of a dividing amniotic membrane between the gestational sacs. The number of yolk sacs was recorded and compared with the presence or absence of a dividing membrane for all fetuses.


RESULTS
In 17/20 (85%) cases of monochorionic diamniotic twins, two yolk sacs were seen. In 3/20 (15%) cases of monochorionic diamniotic twins, a single yolk sac was seen. In the one case of monochorionic diamniotic triplets, two yolk sacs were visualized. In one case of monoamniotic twins, a single yolk sac was observed.


CONCLUSIONS
In monochorionic pregnancies, the presence of two yolk sacs predicts diamnionicity. However, the use of the number of yolk sacs as a predictor of amnionicity may not be accurate in a small proportion of patients. The diagnosis of monoamnionicity can be made only following a careful search for a dividing amniotic membrane.
Shen
O
O
Department of Obstetrics and Gynecology, Shaare Zedek Medical Center, Faculty of Health Sciences, Ben-Gurion University of the Negev, Jerusalem, Israel.
Samueloff
A
A
Department of Obstetrics and Gynecology, Shaare Zedek Medical Center, Faculty of Health Sciences, Ben-Gurion University of the Negev, Jerusalem, Israel.
Beller
U
U
Department of Obstetrics and Gynecology, Shaare Zedek Medical Center, Faculty of Health Sciences, Ben-Gurion University of the Negev, Jerusalem, Israel.
Rabinowitz
R
R
Department of Obstetrics and Gynecology, Shaare Zedek Medical Center, Faculty of Health Sciences, Ben-Gurion University of the Negev, Jerusalem, Israel.
D000650:Amnion / Q000000981:diagnostic imaging / Q000196:embryology*; D005260:Female; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011272:Pregnancy, Multiple / Q000502:physiology*; D014430:Twins, Monozygotic; D016216:Ultrasonography, Prenatal; D015017:Yolk Sac / Q000000981:diagnostic imaging / Q000196:embryology*