Optical properties of human amniotic fluid: implications for videofetoscopic surgery.

OBJECTIVE

Videofetoscopy typically demands the substitution of oft-turbid amniotic fluid with clear crystalloid. This maneuver can be cumbersome and may lead to complications. We sought to determine the optical properties of the amniotic fluid, as a pre-requisite for optimizing video image processing during videofetoscopy and eventually avoid amniotic fluid replacement.

METHODS

Human amniotic fluid samples (n = 21) were procured at 19-36 weeks of gestation. Optical refraction and reflection indices were recorded as percentages of light transmission through the fluid using an integrated spectrometer covering wavelengths of 400-950 nm, with 1.0 nm resolution. Statistical analysis was by one-way ANOVA (p < 0.05).

RESULTS

Peak optical refraction fell within a relatively limited window of the near-infrared spectrum, at 848.1 +/- 52.3 nm, regardless of gestational age or overall light absorbance. Within the visible spectrum, transmission was highest at the highest wavelengths. A statistically significant inverse relationship existed between gestational age and overall light transmission. Light reflection was negligible in all samples.

CONCLUSIONS

Light transmission through amniotic fluid is optimal in the near-infrared spectrum and at the highest visible wavelengths, regardless of gestational age. Overall light transmission through amniotic fluid decreases throughout gestation. The light source and camera of videofetoscopy systems should be designed accordingly, possibly obviating the need for routine intraoperative amniotic fluid exchange.