Deceleration/contraction ratios as an index of fetal health during labor.

Internal FHR tracings of 259 patients with variable decelerations and 49 with late decelerations were analyzed for frequency and severity of the pattern in an attempt to correlate with fetal pH or Apgar score at 1 minute. A significant increase in the risk of fetal acidosis was associated with a frequency of greater than 30% variable decelerations and 20% late decelerations. It also increased with the increase of severity of the pattern. Variable decelerations are not good predictors of Apgar scores less than or equal to 6 at 1 minute, but late decelerations are predictive when they occur more than 20% of the time. The fetus with variable decelerations a normal pH can be observed through the first stage of labor with a high degree of confidence. However, when a 20% or more moderate-to-severe late deceleration/contraction ratio is present, intervention is necessary even if scalp blood pH is normal. The FHR deceleration/uterine contraction (UC) ratio is a simple bedside technique for assessing fetal outcome.