The effect of maternal hypercapnia and hyperoxia on breathing movements in the normal and growth-retarded fetus.

Fifteen normal pregnant subjects inhaled a 7% CO2 mixture over a period of 5 min, resulting in a markedly increased rate of fetal breathing. In a further 15 normal pregnant subjects, an 80% O2 mixture was administered over a period of 10 min; during the second half of this stimulation period a significant increase in fetal breathing rate was noted. Finally, a 7% CO2 mixture was administered during a 5-min period to a total of 26 pregnant patients with fetal growth retardation. Seventeen of these 26 patients were subsequently administered an 80% O2 mixture during a 10-min period, immediately followed by a mixture of 80% O2 and 7% CO2 over a 5-min period. During both maternal hypercapnia and hyperoxia a marked increase in fetal breathing rate was noted, which was not essentially different from that seen in normal pregnancy. Administration of a mixture of O2 and CO2 did not result in any significant change in fetal breathing activity. At birth, all growth-retarded infants had an Apgar score of 6 or more at one minute. It can be concluded that respiration in both the normal and the clinically non-hypoxic growth-retarded fetus shows a similar reaction pattern towards alterations in maternal gaseous exchange.