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BACKGROUND

KEY QUESTIONS

  • Describe the general procedure for obtaining umbilical cord blood gas samples.

  • What information about fetal status is reflected in umbilical artery and vein samples?

  • Name four neonatal signs that are consistent with an acute peripartum or intrapartum event.

  • What is the primary variable that alters fetal oxygenation during the labor course and potentially affects umbilical cord results?

CASE 51-1

A 24-y.o. gravida 1, para 0 at 37 2/7 weeks gestation is admitted for gestational hypertension. Vaginal misoprostol is administered for cervical ripening with a Category I tracing. After 12 hours, oxytocin augmentation is initiated for a protracted active phase. Uterine tachysystole accompanied by an FHR baseline of 185 bpm, minimal variability, and recurrent late decelerations are recorded 3 hours later. Corrective measures are ineffective. An emergency C-section is performed for vaginal bleeding, and a fetal bradycardia ranges from 60–80 bpm. A male infant is delivered weighing 2623 g, with Apgar scores of 1, 2, and 2 at 1, 5, and 10 minutes, respectively. A Grade 2 placental abruption is identified. Umbilical cord blood gas results are shown in Table 51-1. How would you interpret these values?

TABLE 51-1Case Study Umbilical Cord Gas Results

Electronic fetal monitoring to assess adequate oxygen delivery to the fetus occurs in approximately 89% of births in the United States.1 Data obtained from monitoring allows clinicians to potentially identify interruptions in the transfer of oxygenated blood from the environment to the fetus. The focus of monitoring is to identify fetal heart rate (FHR) characteristics that reflect an inadequate oxygen supply so that interventions may be carried out. Interruptions in oxygen delivery can occur at several levels of a pathway, with uterine activity being most common. Most fetuses tolerate brief interruptions, so long as episodes are brief and respond to corrective measures. Over time, if oxygen delivery continues to be interrupted or occurs for longer periods, insufficient oxygen levels could potentially result in fetal hypoxia, and ultimately neurologic injury or death.

Inaccurate interpretation and management decisions concerning FHR and uterine activity patterns may affect fetal oxygenation, specifically acid-base values and metabolic condition at birth. Unfortunately, an insufficient number of prospective electronic fetal monitoring studies validates an association between specific FHR patterns and fetal acidemia. As a result, electronic fetal monitoring's ability to decrease adverse perinatal and neonatal outcomes remains unsupported. Apgar scores, which guide neonatal resuscitation, may not correlate with acid-base status or predict adverse neurologic development because other circumstances, such as prematurity or intra-amniotic infection, may influence acid-base values. Therefore a direct, objective, and sensitive measurement of fetal acid-base status may become necessary at birth to assess the ...

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