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

Abstract

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° versus 43.7 ± 8.9°; 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° versus female fetus, 45.2 ± 8.3°; p = 0.02 and 11–15 weeks male fetus, 48.1 ± 7.0° versus female fetus, 48.4 ± 7.4°, 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.