What should happen to the fetus's heart rate during uterine contractions?

Normal Fetal Heart Rate Response to Contractions

The fetal heart rate should remain stable during contractions with no decelerations in a healthy fetus, maintaining a normal baseline of 110-160 bpm with moderate variability (6-25 bpm). 1

Expected Normal Pattern

• The normal fetal heart rate tracing shows no decelerations in response to uterine contractions, with maintenance of baseline rate and moderate variability throughout labor 2
• The presence of moderate variability (6-25 bpm) during and between contractions is reassuring and predictive of the absence of fetal acidemia 3, 1
• Accelerations (increases in FHR) may occur with contractions or spontaneously, and their presence indicates fetal well-being 4

Abnormal Patterns That Require Attention

When decelerations occur with contractions, they indicate different pathophysiologic processes:

Early Decelerations

• These have a gradual onset that is coincident in timing with the uterine contraction, with the nadir occurring at the peak of the contraction 2
• Early decelerations are generally benign and result from fetal head compression rather than hypoxia 2

Variable Decelerations

• These have an abrupt onset and are variable in timing, duration, and relationship to contractions 2
• Variable decelerations suggest umbilical cord compression and become concerning when recurrent with absent variability 3, 5

Late Decelerations

• These show a gradual decrease in FHR with onset, nadir, and recovery occurring after the onset, peak, and end of the contraction 2
• Late decelerations indicate uteroplacental insufficiency and are particularly ominous when combined with absent variability 3, 5

Clinical Significance of Variability

• Normal FHR variability represents normal central nervous system integrity and adequate oxygenation, even in the presence of some decelerations 5
• The combination of absent baseline variability with recurrent decelerations defines Category III (abnormal) tracings requiring immediate intervention 3, 1
• Moderate variability during contractions provides strong reassurance that physiologic compensations are intact 5

Key Clinical Pitfall

• Do not confuse temporary decreased variability from fetal sleep cycles (20-40 minutes) with pathologic absent variability 3
• The critical distinction is that pathologic patterns show absent variability combined with recurrent decelerations or bradycardia, not isolated findings 3