In this context, it should also be of interest that the frequency and phase co-ordination of the heart rhythms of mother and child in the womb also participate in this nocturnal intensification of the rhythmic functional orders. Thus, it could be proven that, while preg­nant women were asleep at night, not only is the heart rate ratio of mother and child more strictly adjusted to the whole numbered value of 1:2, but that, at the same time, a phase co-ordination sets in during which the child's heart beat prefers certain phases of its mother's heart beat. (illustration 15). At the same time, this example makes the func­tional importance of harmonic co-ordination between rhythmic functions clear, as with correct phase co-ordination, an uneconomical-simultaneous arrival of the mother's and child's pulse waves in the placenta can be avoided.