A Rabbit Model for Optimization of Amniotic Fluid Components in the EXTrauterine Environment for Newborn Development (EXTEND) System

Abstract

In this model article, we present a protocol for continuous amniotic fluid exchange in rabbits using a novel system to test the effects of growth factor-deficient, artificial amniotic fluid on bowel development. <b><i>Background:</i></b> Ideally, the EXTrauterine Environment for Neonatal Development (EXTEND) will provide physiologic support to the extreme premature infant. An important component of that environment is the amniotic fluid. Thus, we developed an animal model to study the growth factors found within amniotic fluid and inform design of a synthetic fluid to optimize fetal development. <b><i>Methods:</i></b> We designed a model of amniotic fluid exchange within the pregnant rabbit, continuously removing the natural fluid from around 2 fetuses per doe and replacing it with a physiologic electrolyte solution during the final 100 h of gestation. Two fetuses from the contralateral uterine horn were used as sham-operated controls. Thirty-eight fetuses were analyzed, 19 in each group. We analyzed the fetal growth and bowel development. <b><i>Results:</i></b> Ultrasound after 100 h of exchange showed equivalent fluid volumes, <i>p</i> = 0.63. Cultures were negative for bacterial colonization. Final fluid protein concentrations were 11.6% that of control fluid (mean 1,451 ± 224.2 vs. 12,491 ± 849.2 μg/mL). There was no significant difference in fetal growth, with experimental weights 91.4% of control weights, <i>p</i> = 0.07. Fetal bowel weights (90.1%, <i>p</i> = 0.16) and lengths (94.2%, <i>p</i> = 0.49) were also not significantly less compared to controls. There was no significant difference in villous height or crypt depth measurements between the groups, and absorptive capacity of the bowel was not different between groups, <i>p</i> = 0.44. <b><i>Conclusion:</i></b> This animal model allows for manipulation of the components of amniotic fluid. Marked reduction of natural amniotic fluid proteins during gestation does not appear to significantly impair fetal growth or bowel development. Further work with this model will assess the importance of amniotic fluid components for normal development to inform design of a synthetic fluid for use during EXTEND.

Artificial womb: a paradigm shift for saving extremely premature infants

“…Most current studies have used a simple electrolyte solution, but amniotic fluid contains many trophic factors and other components that may be beneficial to the fetus. To develop an optimal "amniotic fluid" for optimal fetal growth and development, Baumgarten et al [ 6 ] designed a model of continuous amniotic fluid exchange around a fetal rabbit. Monitoring of fetal development and timely adjustment of the nutrient concentration during the medical practice are of great significance, including checking blood glucose daily, calculating weight gain, or checking insulin-like growth factor (IGF)-1 and IGF binding protein, which can also be treated as an indicator of fetal growth in the management of nutrition.…”