Fetal transcutaneous carbon dioxide tension during the second stage of labour.

Fifteen women were studied during the second stage of labour by measuring simultaneously fetal transcutaneous carbon dioxide tension (Tc PCO2 and maternal end-expiratory PCO2. A linear increase of Tc PCO2 with time was observed, predominantly because of changing maternal respiration patterns. The degree of maternal hyperventilation had no adverse effect on the status of the newborn infant.