Maternal-fetal transfer of indocyanine green across the perfused human placenta

Indocyanine green (ICG) is an FDA-approved near-infrared imaging probe, given also to pregnant women. We aimed to characterize ICG's transplacental transfer using the ex-vivo perfusion model. Placentas were obtained from caesarean deliveries. Cotyledons were cannulated and dually perfused. ICG, 9.6 μg/mL and antipyrine (50 μg/mL) were added to the maternal circulation in the absence (n = 4) or the presence of the organic anion transporting polypeptide (OATPs) inhibitor rifampin (10 μg/mL; n = 5) or the P-glycoprotein inhibitor valspodar (2 μg/mL; n = 3). ICG's maternal-to-fetal transfer was evaluated over 180 min. The cumulative percent of ICG in the fetal reservoir was minor. When ICG transfer was normalized to that of antipyrine, it was lower in the presence of rifampin (a 41% decrease; p < 0.05). Valspodar did not appear to modify the kinetics of ICG. ICG's transplacental transfer is minimal and is probably OATP-mediated. The placenta is an effective protective barrier to ICG's distribution into the fetus.