A nulliparous woman at 38 weeks is in active labour with cervix 7 cm, 100% effaced, vertex at +1 station, and membranes intact. CTG shows repetitive late decelerations with reduced variability. She is taken for emergency caesarean. What is the minimum umbilical cord arterial pH that defines perinatal asphyxia per ACOG criteria?
- A pH < 7.20
- B pH < 7.00 ✓
- C pH < 7.10
- D pH < 6.90
Correct answer: B. pH < 7.00
Explanation
ACOG defines birth asphyxia (pathological fetal acidemia) as umbilical cord arterial pH < 7.00. This threshold is associated with increased risk of neonatal neurological injury and organ dysfunction. A pH of 7.00–7.10 constitutes acidemia but not necessarily pathological asphyxia. HIE and neonatal encephalopathy criteria additionally require a base deficit ≥ 12 mEq/L. The pH < 7.00 threshold is the commonly tested ACOG criterion for birth asphyxia.
Reference: Williams Obstetrics, 26th ed.
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