Association of solar and geomagnetic activity with fetal growth

Background and aim: Solar and geomagnetic activity have been previously shown to suppress melatonin, which is an important hormone for fetal development. We explored whether solar and geomagnetic activity were associated with fetal growth. Methods: We included singleton births with routine ultrasounds at an academic medical center in Eastern Massachusetts from 2011 through 2016. Sunspot number (SSN), interplanetary magnetic field (IMF), and Kp index were obtained from the NASA Goddard Space Flight Center. Three exposure windows were considered, including the first 16 weeks of pregnancy, one month prior to fetal growth measurement, and conception until fetal growth measurement (cumulative). Ultrasound scans from which we extracted biparietal diameter (BPD), head circumference (HC), femur length (FL), and abdominal circumference measurements were categorized as anatomic (<24 weeks’ gestation) or growth scans (≥24 weeks’ gestation). Ultrasound parameters and birth weight were standardized, and linear mixed models adjusted for seasonality, long-term trends, meteorological factors, and maternal characteristics were fitted. Results: Among 9,428 pregnancies, prenatal exposure was negatively associated with ultrasound parameters among growth scans. Associations varied by exposure window, solar metric, and fetal growth parameter. Cumulative exposure to solar and geomagnetic activity was important across exposure metrics, where an interquartile range (IQR) increase in SSN was associated with a -0.20 (95% CI: -0.30, -0.11), -0.28 (95% CI: -0.39, -0.17), and -0.16 (95% CI: -0.26, -0.06) difference in average BDP, HC, and FL z-scores, respectively. Cumulative IMF and Kp index were also associated with reduced average HC, -0.23 (95% CI: -0.36, -0.10) and -0.14 (95% CI: -0.24, -0.03) z-score difference per IQR increase, respectively. Conclusions: Solar and geomagnetic activity were associated with reduced fetal growth. Future studies are needed to better understand the impact of these natural phenomena on clinical endpoints. Keywords: fetal growth, solar activity, pregnancy