EP14.24: Deepest vertical pocket of amniotic fluid in uncomplicated monoamniotic twins: can we use standard charts?

To describe the deepest vertical pocket (DVP) in a cohort of “uncomplicated” monochorionic monoamniotic (MA) twins, in comparison to the well established references for singletons and twins. Retrospective cohort study of all cases of “uncomplicated” MA twins followed at our Multiple Pregnancy Clinic at the Hospital Italiano de Buenos Aires between 2008 and December 2023. Our follow-up includes ultrasound with DVP every 2 weeks until 24-28 weeks, starting ultrasound 3x/week until delivery at 32-33 weeks. We excluded triplets and higher-order pregnancies, and MA with chromosomal abnormalities, major congenital defects, death of one twin, complications of monochorionicity (Twin–twin transfusion syndrome [TTTS], sFGR, TAPS), and maternal conditions that could affect the amniotic fluid volume. We included 13 uncomplicated MA pregnancies, with 111 measurements, with a median of 10 measurements (IQR 7-10.5) per pregnancy. Plotted against the amniotic fluid reference chart used in singletons and twins, no pregnancy had a DVP below the 5th percentile or below 2 cm, 13/13 had a DVP > 95th percentile, and the DVP was > 8 cm in 4/13 (31%) and > 10 cm after 20 weeks in 1/13 (8%). The distribution of DVP measurements in the current cohort of uncomplicated MA pregnancies appears to have somewhat higher values than singleton pregnancies. Amniotic fluid varies with gestation, reaching a maximum at the end of the second trimester. Establishing normal values for DVP in MA twins would be important because structural defects are more common and TTTS is less frequent than in MCDA but the diagnosis is more challenging.