The relationships between fetal heart rate (FHR) patterns and fetal movements (FM) were evaluated in 20 normal fetuses between 20 and 20 weeks' gestation. In 10 fetuses at 20 to 22 weeks' gestational age, 602 of the 620 observed FHR changes (97.1%) were decelerations. In this same group, most of the FHR changes (62.4%) were associated with FM. Similarly, 387 of 569 (68%) recorded FM between 20 and 22 weeks' gestation were associated with FHR changes. In a second group of fetuses between 28 and 30 weeks' gestation, in contrast to the less mature group, 227 of 670 FHR changes (33.9%) were decelerations. Among the remainder of the FHR changes, 240 (35.8%) were accelerations and 203 (30.3%) were accelerations with decelerations. As in the less mature group of fetuses, most of the FHR changes in these older fetuses were associated with FM (81.8%) and 548 of 611 (89.7%) recorded FM were associated with FHR changes. In summary, in normal pregnancy, FHR decelerations are common between 20 and 30 weeks' gestation. With advancing gestation, FHR decelerations are less commonly seen, and the frequency of acceleration and acceleration/deceleration patterns increases. The association between FHR and FM becomes stronger with advancing gestational age between 20 and 30 weeks. These findings suggest that the criteria for evaluating the health of the fetus before 30 weeks may be different from the criteria used later in pregnancy. Consequently, in the evaluation of low-birth weight fetuses between 20 and 30 weeks' gestation, new criteria for normal and abnormal nonstress monitoring tests must be developed.