Fetal health is closely monitored throughout pregnancy and labor to ensure well-being. Monitoring aims to identify signs that the fetus is not receiving adequate oxygen or nutrients, a condition historically called “fetal distress.” The medical community now uses more precise terminology, reflecting a better understanding of the underlying physiology. This article explains the current medical language, the causes, detection methods, and treatments used for a safe delivery.
Defining the Condition and Modern Terminology
The term “fetal distress” is imprecise and has largely fallen out of favor with healthcare providers. Modern obstetrics prefers specific phrases like “Nonreassuring Fetal Status” (NRFS) or “Fetal Compromise” to describe concerning findings. This vocabulary change occurred because the binary term “distress” did not reflect the varying degrees of severity.
NRFS indicates the fetus may be experiencing reduced oxygen supply, known as hypoxia. When hypoxia is severe or prolonged, the fetus shifts from aerobic to anaerobic metabolism. This process creates lactic acid as a byproduct, which accumulates in the fetal bloodstream.
The accumulation of lactic acid leads to metabolic acidosis, disrupting the blood’s acid-base balance. This acid buildup is a physiological concern, as it can be harmful to fetal organs, particularly the brain. The goal of monitoring and intervention is to prevent or reverse this progression from suspected hypoxia to established acidosis.
Common Causes of Fetal Compromise
Compromise occurs when the supply chain of oxygen and nutrients from the mother to the fetus is interrupted. Placental issues are a frequent source of concern, as the placenta is responsible for all gas and nutrient exchange. Conditions like placental abruption, where the placenta prematurely separates from the uterine wall, or placental insufficiency, involving poor blood flow, can drastically reduce oxygen delivery.
The umbilical cord can also cause problems, particularly during labor contractions. Compression of the cord, due to a knot or entanglement, can temporarily or permanently block blood flow. Umbilical cord prolapse, where the cord slips into the birth canal ahead of the baby, creates severe compression requiring immediate attention.
Maternal health factors also affect fetal oxygenation. Conditions such as severe low blood pressure, preeclampsia, or uncontrolled diabetes can impair blood flow to the uterus and placenta. Uterine hyperstimulation, characterized by contractions that are too frequent or too strong, can reduce the resting time needed for the placenta to refill with oxygenated blood.
Detection Through Monitoring
Healthcare providers primarily identify potential fetal compromise by continuously monitoring the fetal heart rate (FHR), typically using a cardiotocograph (CTG). The FHR tracing provides valuable information about the fetus’s oxygenation status. A normal FHR tracing shows a baseline rate between 110 and 160 beats per minute, with moderate variability. This variability, an unevenness in beat-to-beat timing, signifies a healthy nervous system response.
Abnormal FHR patterns are categorized by severity. Late decelerations, which are drops in the heart rate that begin after a contraction starts and recover after it ends, suggest poor placental blood flow. Minimal or absent heart rate variability can signal that the fetal nervous system is suppressed due to lack of oxygen.
Other diagnostic clues assess fetal status, especially outside of labor. Meconium staining, the presence of the fetus’s first stool in the amniotic fluid, is sometimes associated with compromise, though it is not a definite sign of hypoxia. In non-labor settings, an ultrasound-based assessment called a Biophysical Profile (BPP) evaluates four parameters: fetal breathing, body movements, muscle tone, and amniotic fluid volume.
Medical Interventions and Delivery
Once the medical team identifies nonreassuring signs, they implement intrauterine resuscitation steps aimed at improving the fetal environment. The first conservative measure is changing the mother’s position, usually moving her to her side, to relieve pressure on the large blood vessels supplying the uterus. This action often increases blood flow to the placenta.
Supplemental oxygen is administered to the mother, increasing the oxygen carried by her blood to the placenta. Increasing intravenous (IV) fluid delivery helps improve the mother’s blood volume and circulation, enhancing blood flow to the uterus. If the mother is receiving medication to stimulate labor, such as oxytocin, the team will reduce or stop the infusion to allow the uterus to relax and oxygenate the placenta more effectively.
If these conservative measures fail to improve the FHR tracing and compromise persists, urgent intervention is necessary. When the fetus is in a persistent state of hypoxia and progressing toward acidosis, rapid delivery is the safest course. This may involve an assisted vaginal delivery using instruments like a vacuum extractor or obstetric forceps to expedite the birth. If immediate vaginal delivery is not possible or the compromise is severe, an emergency Cesarean section is necessary to resolve the condition and ensure the baby’s safety.