48 Obstetrics and Gynecology Board Review •••
❍ What is a late deceleration?
Visually apparent, usually symmetrical and gradual decrease and return of FHR. Cause: Uteroplacental
insufficiency
Characteristics:
- Deceleration is delayed in timing with respect to the contraction; nadir of decelerations occurs after peak of contraction.
- Onset to nadir ≥30 seconds.
❍ What is a prolonged deceleration?
Visually apparent decrease in FHR that lasts ≥2 minutes but >10 minutes.
❍ What are recurrent decelerations?
When they occur with ≥50% of contractions in any 20-minute window.
❍ What are periodic decelerations?
Decelerations associated with contractions.
❍ What are episodic decelerations?
Decelerations not associated with contractions.
❍ How are uterine contractions quantified?
- Number of contractions in a 10-minute window, averaged over 30 minutes.
- Normal: ≤5 contractions in 10 minutes, averaged over 30 minutes.
- Tachysystole: >5 contractions in 10 minutes, averaged over 30 minutes.
❍ What defines a FHR Category I tracing?
Includes all the following:
- Baseline heart rate: 110 to 160 bpm.
- Variability: Moderate.
- Accelerations: Present or absent.
- Early decelerations: Present or absent.
- Late or variable decelerations: Absent.
❍ What defines a FHR Category II tracing?
Includes all FHR tracings not categorized as Category I or III:
- Baseline:
- Bradycardia not accompanied by absent variability
- Tachycardia
- Variability:
- Minimal
- Absent variability not accompanied by recurrent decelerations
- Marked variability
- Accelerations:
- Absent