Continuous meconium monitoring during labour using an intrauterine probe

The fetus discharges meconium (its bowel contents) into the amniotic fluid during labour in approximately 10% of pregnancies. In about 10% of cases where meconium is passed, the fetus gasps, inhaling the sticky meconium into the upper respiratory tract. After birth, the meconium blocks the air passages in the lungs, impairing gas exchange (meconium aspiration syndrome, MAS). Up to 20% of infants suffering from MAS die and recently published studies have shown a long-term effect of MAS in causing cough and wheeze. At present, meconium is only noticed at birth or occasionally when amniotic fluid leaks past the presenting part of the fetus. We have developed a system to monitor meconium continuously during labour, using a flexible intrauterine probe. The system provides a measurement of the meconium concentration of amniotic fluid during labour every 2 min, with a 60% prediction interval of +/- 10 g l-1, and a 99% prediction interval of +/- 30 g l-1 (clinically 'thick meconium' contains around 100 g l-1). The noise of the measurement is of the order of +/- 10 g l-1, and the response to changes in the meconium concentration is from 40 to 120 s, depending on its configuration. The system also provides other obstetric variables such as fetal heart rate and uterine activity measurement, obtained from a fetal monitor. Preliminary clinical results indicate that this system can measure meconium not apparent to the attending staff; the system can detect changes in the meconium concentration of amniotic fluid; the measurements are confirmed by visual observation at delivery; and changes of meconium concentration seem to correlate with known stressful stimuli. The system therefore provides a new tool from which new variables are obtained, which can greatly enhance clinical research into the pathophysiology of meconium passage and aspiration.