1129 How useful is assessment of amniotic fluid volume in antenatal surveillance of fetal growth restriction?

Abstract

Maximum vertical pocket (MVP) is commonly assessed for surveillance of fetal growth restriction (FGR) and small for gestational age (SGA). It is theorized that MVP becomes compromised when blood flow to the brain is prioritized. Our objectives are to evaluate the relationships among FGR and SGA, MVP, and perfusion parameters. This is a retrospective study of the last ultrasound prior to delivery of 105 fetuses with an estimated fetal weight <10th percentile. Data include biometry, MVP, middle cerebral artery Doppler peak systolic velocities (MCA-PI), and cardiac size, shape, and right-to-left disproportion. Fetuses were classified as FGR or SGA by International Society of Ultrasound in Obstetrics and Gynecology criteria. MCA-PI <10th percentile for gestational age was abnormal. Relationships between dichotomized and continuous variables were analyzed using Fisher’s exact tests and linear regressions respectively. Mean gestational age at time of ultrasound assessment was 36 +/- 2 weeks. A total of 61 (58%) and 44 (42%) fetuses met criteria for FGR and SGA respectively. Five fetuses (5%) had low or low-normal MVPs (≤3cm). MVP ≤3cm did not correspond to increased rate of FGR or abnormal MCA-PI (p=0.39 and 0.31 respectively). The risk ratio (RR) of FGR for MVP ≤3cm compared to MVP >3cm is 1.40 [95% confidence interval (CI) 0.88, 2.25], and the RR of MCA <10th percentile for MVP ≤3cm compared to MVP >3cm is 1.89 [CI 0.60, 5.89]. Cardiac deformation was present in all fetuses with MVP ≤3cm (table). In our series, MVP ≤3cm was found infrequently in fetuses with FGR. There were no differences in MVP between fetuses with FGR v. SGA. Low MVP was not associated with abnormal MCA-PI, contrary to the theorized competitive relationship between amniotic fluid production and fetal brain sparing. However, this pilot study suggests that MVP ≤3cm is associated with fetal cardiac deformation, indicating possible compromise of renal perfusion in the setting of cardiac remodeling; further research is needed to validate this relationship.