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

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
Bucklin, B. (2007). Fetal Distress. Complications in Anesthesia, 770-773. doi:10.1016/b978-1-4160-2215-2.50197-6
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