Gestational age‐specific reference ranges for amniotic fluid assessment in monochorionic diamniotic twin pregnancies

• Published in: Ultrasound in obstetrics & gynecology 2013-06, Vol.41 (6), p.649-652
• Main Authors: DeKoninck, P., Deprest, J., Lewi, P., Richter, J., Galjaard, S., Van Keirsbilck, J., Van Calsteren, K., Lewi, L.
• Format: Article
• Language: English
• Subjects: Adult; Amnion - diagnostic imaging; amniotic fluid; Amniotic Fluid - diagnostic imaging; Analysis of Variance; Female; Fetofetal Transfusion - diagnostic imaging; Gestational Age; Humans; monochorionic twin; Polyhydramnios - diagnostic imaging; Pregnancy; Pregnancy, Twin; reference range; Reference Values; single deepest pocket; transfusion; Twins, Monozygotic; Ultrasonography; Young Adult
• ISSN: 0960-7692; 1469-0705
• DOI: 10.1002/uog.12387

ABSTRACT Objectives To establish gestational age‐specific reference ranges for amniotic fluid measurements in monochorionic diamniotic twin pregnancies, to compare them with previously reported singleton and twin reference ranges and to examine the rationale for using a gestational age‐dependent cut‐off to define polyhydramnios in twin–twin transfusion syndrome, as is the practice in most European centers. Methods We retrospectively evaluated amniotic fluid volume in 32 monochorionic diamniotic twin pregnancies that were followed longitudinally at 2‐week intervals from the first trimester until birth. Amniotic fluid volume was assessed by measuring the deepest vertical pocket in both amniotic sacs. We used multilevel modeling to estimate the gestational age‐specific reference ranges for deepest vertical pocket measurements. Results Based on 429 observations in 64 fetuses, we constructed gestational age‐specific reference ranges from 11 weeks until term. The deepest pocket increased from the first trimester to reach a maximum at 26 weeks, followed by a gradual decrease towards term. Measurements between 18 and 28 weeks were comparable to those in singleton pregnancies. However, before 18 weeks values were higher, whereas after 28 weeks they were lower, as compared to singleton references. Conclusion In monochorionic twin pregnancies, the deepest vertical pocket is a gestational age‐dependent measurement. Therefore, a gestational age‐dependent definition of polyhydramnios in twin–twin transfusion syndrome, as used by most European centers, seems a logical approach. Copyright © 2013 ISUOG. Published by John Wiley & Sons Ltd.