A METHOD FOR CONTINUOUS MONITORING OF MECONIUM IN THE AMNIOTIC-FLUID DURING LABOR

In about 10% of pregnancies overall, the fetus discharges meconium (it s bowel contents) into the amniotic fluid during labour. In about 10% of cases where meconium is Passed, the fetus gasps, inhaling the stick y meconium into the upper respiratory tract. After birth the meconium blocks the air passages in the lungs, impairing gas exchange - meconiu m aspiration syndrome (MAS). Up to 20% of infants suffering from MAS d ie and recently published studies have shown a long-term effect of MAS in causing cough and wheeze. The risk of meconium aspiration is thoug ht to be increased by intrauterine hypoxia. At present, meconium is on ly noticed at birth or occasionally when amniotic fluid leaks past the presenting part of the fetus. A method has been developed which measu res absolute meconium concentration with a 99% prediction internal of +/- 30 g l-1; allows monitoring of the rate of appearance of meconium linearly with a nonlinearity of 5%, and differentiates between meconiu m and blood. The method uses the ratio of the intensity of back-scatte red light from the amniotic fluid at 700 and 415 nm, the latter being near the peak of light absorption by meconium and the former a referen ce value. The ratio is also affected by the presence of blood However, blood has specific absorption peaks at 540 and 575 nm from which it c an be detected (the presence of blood is also a significant abnormalit y, and is relatively uncommon). The measurement method could easily be integrated into an optical sensor mounted onto an intrauterine probe. The measurement of back-scattered light at 415, 540 and 700 nm would allow continuous monitoring of meconium which could provide valuable i nformation for the study of the pathophysiology of meconium Passage in utero during labour and allow preventative measures to be developed.