Fetal cardiac axis in non-anomalous pregnancies: does fetal gender or maternal body mass index (BMI) matter?

Objectives: To determine if cardiac axis obtained at an early ultrasound study (11-15 weeks) differs from that obtained at a late ultrasound study (18-22 weeks) in the same fetus and to evaluate the impact of fetal gender and/or maternal body mass index (BMI). Methods: Cardiac axes of 324 non-anomalous fetuses at 11-15 weeks gestation were measured, with follow-up measurements obtained at 18-22 weeks. Comparisons were performed based on gestational age period, fetal gender and obese/non-obese maternal status. Results: (1) Mean fetal cardiac axis did not change between 11 and 15 weeks; p = 0.8, (2) mean fetal cardiac axis was more levorotated at 11-15 weeks than measurements obtained at 18-22 weeks; 48.1 +/- 7.1 degrees versus 43.7 +/- 8.9 degrees; p<0.0001, (3) male fetuses had less levorotated cardiac axis than female fetuses in late ultrasound studies but there was no difference between them at early ultrasound studies; 18-22 weeks male fetus, 42.7 +/- 9.3 degrees versus female fetus, 45.2 +/- 8.3 degrees; p = 0.02 and 11-15 weeks male fetus, 48.1 +/- 7.0 degrees versus female fetus, 48.4 +/- 7.4 degrees, p = 0.7, respectively, and (4) similar trends with the overall study population were observed in the comparison between fetuses of obese and non-obese women. Conclusion: Fetal cardiac axis remains stable at 11-15 weeks, becoming less levorotated at 18-22 weeks. This may be attributed to increments in fetal lung volume. The differences in cardiac axis measurements between male and female fetuses examined at 18-22 weeks may also be attributable to differences in increment of fetal lung volume during this gestational age period.