Spectrophotometric determination of meconium concentration in amniotic fluid

When a fetus is acutely distressed, for example as a result of strangulation by the umbilical cord, the bowel content, meconium, may be passed into the amniotic fluid. Assessment of meconial contamination of the amniotic fluid is important in the management of late pregnancy. Fresh or increasing meconium content is an indication for urgent delivery. 'Old' meconium is usually distinguished from 'new' by visual inspection of the stained amniotic fluid; a more objective method could have advantages. We consider the effects of meconium staining of amniotic fluid on the spectrophotometric properties of the liquor. The absorption spectra of meconial amniotic fluids reveal an excess absorption band, centred around 410 nm. Quantification of the band height is proposed and it is shown that the height is linearly related to meconium concentration, with a proportionality factor, or sensitivity, of 0.046 ± 0.009 (mean ± s.d.) optical density (OD) units per g l^-1. This sensitivity factor may be used to estimate meconium concentration in samples of amniotic fluid.