Fetal heart rate pattern interpretations are subjective. hus, the potential for computer assistance to enhance the precision of identiying abnormal patterns appeared promising. he INFANT Collaborative Group (2017) studied whether the addition of computer-based decision-support software for interpretation of fetal heart rate patterns lowered the number of poor neonatal outcomes. In this trial, 23,515 women were randomized to computer-assisted interpretation compared with 23,055 women in a conventional clinical interpretation arm. Perinatal outcomes such as intrapartum stillbirth, early neonatal death, and neonatal encephalopathy were not improved by computer assistance. Cesarean delivery rates were similar in both groups. Moreover, a 2-year follow-up of a subset of the surviving children showed no diferences in their neurological development.
According to the American College of Obstetricians and Gynecologists (2017a), measurements of the pH in capillary scalp blood may help identiy the fetus in serious distress. However, this group also emphasizes that neither normal nor abnormal scalp pH results are predictive of neonatal outcome. Notably, the procedure is now used uncommonly and is not available at most hospitals in the United States.
With sampling, an illuminated endoscope is inserted through the dilated cervix after membrane rupture and is pressed irmly against the fetal scalp (Fig. 24-22). The skin is wiped clean with a cotton swab and coated with a silicone gel, which allows fetal blood to accumulate s discrete globules. An incision is made through the fetal scalp to a depth of 2 mm with a special blade on a long handle. As a drop of blood forms on the surface, it is immediately collected into a heparinized glass capillary tube . The pH of the blood is measured promptly.
FIGURE 24-22 The technique of fetal scalp sampling using an amnioscope. The end of the endoscope is displaced from the fetal vertex approximately 2 cm to show the disposable blade against the fetal scalp before incision.
The pH of fetal capillary scalp blood is usually lower than that of umbilical venous blood and approaches that of umbilical arterial blood. In one algorithm, if the pH is :7.25, labor is observed, and if between 7.20 and 7.25, the pH measurement is repeated within 30 minutes (Zalar, 1979). If the pH is <7.20, another scalp blood sample is collected immediately, and the mother is taken to an operating room and prepared for surgery. Delivery is performed promptly if the low pH is conirmed. Otherwise, labor is allowed to continue, and scalp blood samples are repeated periodically.
he only beneits reported for scalp blood pH testing are fewer cesarean deliveries for fetal distress (Young, 1980b). However, Goodwin and coworkers (1994) showed a decrease in the scalp pH sampling rate from approximately 1.8 percent in the mid-1980s to 0.03 percent by 1992. This drop in sampling rate was not associated with a higher cesarean delivery rate for fetal distress. They concluded that scalp blood pH sampling was unnecessary.
Kruger and colleagues (1999) have advocated the use of fetal scalp blood lactate concentration as an adjunct to pH. WibergItzel and associates (2008) randomly assigned 1496 fetuses to scalp blood pH analysis and 1496 to scalp blood lactate analysis. They found either to be equivalent in predicting fetal acidemia. The advantage of lactate measurement was that a smaller amount of blood was needed, which led to a lower procedural failure rate compared with scalp blood sampling for pH.