Acute Fetal Distress

Acute fetal distress is a serious complication in the perinatal period, indicating hypoxia of the fetus [1]. It may result from interference of oxygen transport at the level of the mother, the placenta, the umbilical cord, or the fetus itself [2]. Common high-risk obstetric conditions that increase the risk of fetal distress include preeclampsia, chronic hypertension, and diabetes mellitus [2]. Hypertension during pregnancy is the most common maternal factor to cause fetal distress [1]. Placental abruption and placental previa are the most common placental factors to cause fetal distress [1]. Low fetal oxygen often leads to heart, lung, and brain damage of the fetus [1]. Prolonged periods of fetal distress can result in fetal death due to neonatal asphyxia [1].

Accurate diagnosis of fetal distress continues to be a clinical challenge [2]. Traditionally, electronic fetal heart rate monitors have been the primary tool used to screen for fetal distress [2]. Gradual declines in fetal oxygenation produce a variety of distinct heart rate patterns [2]. Early signs of hypoxia may include tachycardia, persistent sinusoidal fetal heart rate pattern, and periodic changes consisting of late and variable decelerations [2]. Profound decreases in fetal oxygenation often result in bradycardia, usually less than 90 beats per minute [2]. In extreme cases of fetal distress, fetal heart rate pattern may reveal a straight-line tracing devoid of accelerations, variability, and decelerations [2]. However, the diagnosis of fetal distress based on heart rate is imprecise with poor sensitivity [3]. Additional support for the diagnosis of fetal distress may be obtained from the presence of meconium in the amniotic fluid, declining fetal acid-base status, lack of fetal heart rate response to stimulation, and umbilical artery Doppler velocimetry [2].

Evaluation of the characteristics of umbilical cord blood flow with ultrasound may provide references for the prediction and diagnosis of fetal distress [1]. A 2016 study analyzed the significance of umbilical cord blood flow in 52 patients with acute fetal distress from May 2012 to August 2015 [1]. Researchers placed an ultrasound probe at the ventral side of the fetus to determine characteristics of umbilical artery blood flow [1]. The systolic/diastolic (S/D) ratio, resistance index (RI), and pulsatility index (PI) were calculated [1]. When acute fetal distress occurred, RI, PI, and S/D of the pregnant women were shown to be significantly elevated, indicating increased vascular resistance and decreased blood flow in vessels [1]. Therefore, changes in umbilical blood flow detected by ultrasound are highly predictive of intrapartum fetal distress [1].

Immediate intervention is needed to optimize neonatal outcome in settings of acute fetal distress [4]. There is currently no treatment for acute fetal distress other than urgent operative delivery of the fetus [4]. Interventions to improve fetal oxygenation during labor include maternal hyperoxygenation using 100% oxygen, maternal repositioning, intravenous fluid administration, amnioinfusion, tocolysis, and intermittent pushing [4].

References

1. Dai, W., Xu, Y., Ma, X. et al. (2016). Ultrasonic characteristics and clinical significance of umbilical cord blood flow in acute fetal distress. Journal of Acute Disease, 5(6), 483-487. doi:10.1016/j.joad.2016.07.003
2. Bucklin, B. (2007). Fetal Distress. Complications in Anesthesia, 770-773. doi:10.1016/b978-1-4160-2215-2.50197-6
3. Vannuccini, S., Bocchi, C., Severi, F., & Petraglia, F. (2016). Diagnosis of Fetal Distress. Neonatology, 1-23. doi:10.1007/978-3-319-18159-2_156-1