Longitudinal assessment of amniotic fluid volume in monoamniotic twin gestations

Objective: The aim of this study is to describe normal amniotic fluid volume through gestation in a cohort of normal monoamniotic (MA) twins. Method: Our ultrasound database was queried for MA twin gestations from 2004 to 2011. Monochorionic twin pregnancies mimicking MA gestations, such as twin-twin transfusion syndrome, were excluded. Complicated MA gestations and higher-order multifetal gestations involving an MA pair were excluded. Thirty subjects were followed with serial amniotic fluid index (AFI) measurements from 15 to 32weeks gestation. Using each AFI measurement as a unique data point, a quadratic regression model and a multi-level growth model were developed against gestational age (GA), providing a predicted AFI at each completed week, with a 95% confidence interval. Results: The quadratic regression least squares and multi-level growth models yielded the same curve comparing the AFI to the GA. Figure1 depicts the model with the 95% confidence interval for normal amniotic fluid volume by GA for normal MA twins. Table2 shows the 5th, 50th, and 95th percentiles for AFI by week from 15 to 32weeks. Conclusion: We have generated normative data for amniotic fluid volume across gestation in uncomplicated MA twins. This can be used as a reference when managing MA pregnancies.