As pregnancy progresses, the amniotic fluid becomes more turbid. This can be semiquantitated by measuring its absorbance at 650 nm. It correlates with the increase in lamellar bodies, which serve to scatter light and thus make the fluid appear turbid.


Specimen: Amniotic fluid, protected from light


Testing: Spectrophotometric absorbance of amniotic fluid at 650 nm.



• optical absorbance >= 0.1 indicates maturity



(1) heme pigment

(2) porphyrins

(3) bilirubin



• Polyhydramnios results in false negative values due to dilutional effect.


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