Associations of solar activity and related exposures with fetal growth

Solar and geomagnetic activity have been shown to suppress melatonin and to degrade folate levels, important hormones for fetal development. We examined whether solar and geomagnetic activity were associated with fetal growth.

We included 9573 singleton births with 26,879 routine ultrasounds at an academic medical center in Eastern Massachusetts from 2011 through 2016. Sunspot number 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, head circumference, femur length, and abdominal circumference measurements were categorized as anatomic (<24 weeks' gestation) or growth scans (≥24 weeks' gestation) based on clinical practice. Ultrasound parameters and birth weight were standardized, and linear mixed models adjusted for long-term trends were fitted.

Prenatal exposures were positively associated with larger head parameters measured <24 weeks' gestation, negatively associated with smaller fetal parameters measured ≥24 weeks' gestation, and not associated with birth weight. The strongest associations were observed for cumulative exposure in growth scans, where an interquartile range increase in sunspot number (32.87 sunspots) was associated with a -0.17 (95 % CI: -0.26, -0.08), -0.25 (-0.36, -0.15), and -0.13 (95 % CI: -0.23, -0.03) difference in mean biparietal diameter, head circumference, and femur length z-score, respectively. An interquartile range increase in cumulative Kp index (0.49) was associated with a -0.11 (95 % CI: -0.22, -0.01) and -0.11 (95 % CI: -0.20, -0.02) difference in mean head circumference and abdominal circumference z-score, respectively, in growth scans.

Solar and geomagnetic activity were associated with fetal growth. Future studies are needed to better understand the impact of these natural phenomena on clinical endpoints.