The probability of fetal metabolic acidosis during labor in a population at risk as determined by clinical factors.

The clinical data derived from 2,772 pregnancies managed in an intrapartum intensive care unit have been analyzed to establish which criteria will indicate in a more definite manner the probability that fetal metabolic acidosis will occur during labor and delivery. All antepartum and intrapartum clinical factors indicate a pregnancy and fetus with an increased probability of fetal metabolic acidosis. However, there is a remarkably consistent relationship between decreasing fetal weight in each week of gestational age and in increasing probability of fetal metabolic acidosis that will permit the magnitude of the risk to be determined with greater precision. The following clinical guidelines are proposed: (1) Current antepartum and intrapartum risk factors are appropriate for the selection of patients for intrapartum intensive care. (2) An accurate gestational age and an estimate of fetal weight within 200 gm will provide an indication of the probability of fetal metabolic acidosis in the individual fetus ranging from 15% to 50%. (3) The presence of meconium in the amniotic fluid increases the probability of metabolic acidosis as defined by fetal weight in relation to gestational age.