The changes in fetal habituation patterns due to a decrease in inspired maternal oxygen.

Habituation is widely regarded as a basic form of learning. A fully functioning central nervous system is probably required for a normal habituation pattern. Habituation of the behavioural response to vibroacoustic stimulation was studied in 23 normal human fetuses whose gestational age was 36 or more weeks. Eighteen were tested whilst their mothers breathed either air or a 12% oxygen in nitrogen mixture. The test was repeated the following day with the order of the gases reversed. In addition five fetuses were tested while their mothers breathed air on both occasions. Of the 18 fetuses 17 had a normal habituation pattern when tested in air but only two had a normal pattern when their mothers breathed 12% O2. Four of the five fetuses tested both days in air had normal patterns on the second day. Altering the amount of inspired maternal O2 alters the fetal habituation pattern.