Incidence of spontaneous and evoked fetal movements in the first half of twin pregnancy.

Fetal movements (FM) may be spontaneous, originating in the fetus itself, or evoked, caused by external stimuli. The FM in 21 normal twin pregnancies at 10 and 21 weeks of gestation were studied. The percentage rate of evoked FM which occur simultaneously in both twins was 4.96% of all observed FM. The rate of the spontaneous FM which occur independently in each fetus was 95.04% of all FM. The low incidence of evoked FM, at an early gestational age (10-21 weeks) emphasizes the ability of these young fetuses to perceive external stimuli and to react to them by FM.