The fidgety fetus hypothesis: Fetal activity is an additional variable in determining birth weight of offspring of women with diabetes

OBJECTIVE - To determine whether some offspring of women with diabetes are intrinsically more active than others in utero and whether those who are active are able to normalize their birth weight despite maternal hyperglycemia. RESEARCH DESIGN AND METHODS - We conducted a three-phase study to view the relationship between fetal movements and subsequent birth weight in women with diabetes. Phase I was designed to assess maternal perception of fetal movements in a population of 10 women with diabetes. To improve our fetal monitoring techniques, in phase II we analyzed fetal movements using the Card Guard home fetal monitoring device (CG 900P) in a population of 13 women with gestational diabetes mellitus (GDM). To apply our observations of fetal movements to a larger population, during phase III we conducted a retrospective analysis of fetal monitoring strips (HP 8041A) from 46 women with GDM to examine the relationship between fetal heart rate (FHR) accelerations and percentile birth weight, corrected for gestational age. RESULTS - Phase I confirmed that there is little variability in fetal movements (i.e., fetal kicks did not significantly deviate from one another on a day-to-day basis). In phase II, the fetal monitoring strips illustrated that the active fetuses (defined as ≥4 FHR accelerations in a 20-min period) were always active, and the inactive fetuses were always inactive. The mean birth weight percentile, corrected for gestational age, in the active group was 37 vs. 63% in the inactive group (P = 0.05). In phase III, the fetal monitoring strips showed an inverse correlation between the mean number of FHR accelerations and the birth weight of the fetus, corrected for gestational age. The mean birth weight percentile in the active group was 37 vs. 62% in the inactive group (P = 0.0017). CONCLUSIONS - The fetus appears to play a role in determining its own destiny. Increased fetal activity may minimize the impact of hyperglycemia on subsequent birth weight. The inactive fetus appears to be at a higher risk for glucose-mediated macrosomia.