Chestnut Chapter 8- Lesson 6

• Fetal assessment during labor is challenging, requiring optimized outcomes with minimized maternal interventions.

Fetal Risk During Labor

• Intrapartum stillbirths account for 1.3 million perinatal deaths yearly, with a range of 10% to 50% of all stillbirths in developed and developing countries.
• An increase in cesarean delivery rates up to 15% correlates with a decrease in intrapartum stillbirth rates by 1.61/1000.
• Fetal hypoxia in utero can cause neurologic injuries, seen in studies of monkeys suffering neurologic injuries similar to those seen in children
• 20% of pregnant women considered high-risk account for 50% of perinatal morbidity and mortality cases.
• High-risk pregnancies include; maternal medical complications, fetal complications, and intrapartum complications
• Risk scoring systems have not demonstrated improved pregnancy outcomes due to inadequate sensitivity and poor positive predictive values.
• 70% fetal neurologic injuries come from events before labor, like congenital anomalies, chemical exposure, or infection.
• Only 4% of neonatal encephalopathy cases result solely from intrapartum hypoxia, with incidence being 1.5/1000.
• Acute intrapartum hypoxic-ischemic events can cause neonatal encephalopathy
• Obstetricians need clear definitions of intrapartum injury with improved monitoring tech and standardized interpretation to enhance ascertainment of the fetus at risk to correct reversible pathophysiology.
• Placental transfer is affected by concentration gradients, villus surface area, placental permeability, and placental metabolism.
• Uterine contractions can decrease uteroplacental blood flow, leading to fetal asphyxia in borderline placentas.
• Compensatory responses of the fetus to hypoxia include decreased oxygen consumption and redistribution of blood flow to key organs.

Electronic Fetal Heart Rate Monitoring

• FHR monitored intermittently with a stethoscope or continuously using Doppler ultrasonography or fetal ECG.
• Parasympathetic outflow decreases FHR, while sympathetic activity increases FHR and cardiac output.
• Electronic monitors record FHR and uterine contractions, determining baseline rate and patterns.
• Doppler ultrasonography detects changes in ventricular wall motion and blood flow in major vessels.
• FHR is calculated using the intervals between fetal myocardial contractions or successive R-R intervals from scalp electrodes.
• Uterine contractions monitored externally or internally using devices like tocodynamometers or intrauterine pressure catheters.
• Normal contraction frequency is ≤5 in 10 minutes; tachysystole is >5 contractions in 10 minutes and utilizing electrohysterography may decrease the need for intrauterine pressure catheter placement.
• FHR pattern features: baseline measurements, variability, accelerations, and decelerations.
• Normal baseline FHR is 110-160 bpm., lower in term fetuses due to parasympathetic activity.
• Bradycardia can be caused by increased vagal activity is the response to acute hypoxemia and maternal medications like atropine.
• Variability reflects intact pathways from fetal cerebral cortex, midbrain, vagus nerve, and cardiac conduction system and parasympathetic tone influencing variability.
• Hypoxemia reduces variability and normal variability predicts early neonatal health
• Decreased variability includes fetal hypoxia, sleep state, neurologic abnormality, and drug exposure
• Accelerations are abrupt FHR changes from baseline and acceleration that extends for 2 minutes is prolonged, at 10 minutes considered baseline change
• FHR accelerations during the antepartum period signal fetal health, but less clear during intrapartum.
• Accelerations may indicate a vulnerable umbilical cord, but commonly preclude fetal acidosis.

Decelerations

• Early decelerations coincide with contractions, caused by reflex vagal activity, and are not ominous.
• Late decelerations begin after contractions, due to hypoxemia or myocardial failure
• Late decelerations combined with decreased FHR variability signal fetal compromise.
• Variable decelerations vary in depth, shape, and duration, result from umbilical cord occlusion or head compression
• Some practitioners use atypical patterns to describe decelerations but may not always indicate additional hazard for the fetus.
• Sinusoidal patterns may signal fetal anemia