Comparison of Serial Amnioinfusion Strategies for Isolated Early-Onset Fetal Renal Anhydramnios

The optimal protocol for serial amnioinfusions to maintain amniotic fluid in pregnancies with early-onset fetal renal anhydramnios before 22 weeks is not known. We compared the performance of two different approaches.

A secondary analysis was conducted of serial amnioinfusions performed by a single center during the external pilot and feasibility phases of the Renal Anhydramnios Fetal Therapy (RAFT) trial. During the external pilot, higher amnioinfusion volumes were given less frequently; in the feasibility study, smaller volume amnioinfusions were administered more frequently. Procedural details, complications, and obstetric outcomes were compared between the two groups using Pearson's χ2 or Fisher's exact tests for categorical variables and Student's t tests or Wilcoxon rank-sum tests for continuous variables. The adjusted association between procedural details and chorioamniotic separation was obtained through a multivariate repeated measure logistic regression model.

Eleven participants underwent 159 amnioinfusions (external pilot: 3 patients, 21 amnioinfusions; feasibility: 8 patients, 138 amnioinfusions). External pilot participants had fewer amnioinfusions (7 vs. 19.5 in the feasibility group, p = 0.04), larger amnioinfusion volume (750 vs. 500 mL, p < 0.01), and longer interval between amnioinfusions (6 [4-7] vs. 4 [3-5] days, p < 0.01). In the external pilot, chorioamniotic separation was more common (28.6% vs. 5.8%, p < 0.01), preterm prelabor rupture of membranes (PPROM) occurred sooner after amnioinfusion initiation (28 ± 21.5 vs. 75.6 ± 24.1 days, p = 0.03), and duration of maintained amniotic fluid between first and last amnioinfusion was shorter (38 ± 17.3 vs. 71 ± 19 days, p = 0.03), compared to the feasibility group. While delivery gestational age was similar (35.1 ± 1.7 vs. 33.8 ± 1.5 weeks, p = 0.21), feasibility participants maintained amniotic fluid longer.

Small volume serial amnioinfusions performed more frequently maintain normal amniotic fluid volume longer because of delayed occurrence of PPROM.