Solar activity and number of live births in Massachusetts neonates 2000-2015

BACKGROUND AND AIM: Previous studies have shown a possible effect of solar energy on pregnancy and fetal growth. The objective of the present study is to investigate the impact of solar and geomagnetic activity on the number of live births in Massachusetts, USA neonates during 2000 to 2015. METHODS: Non-linear distributed lag models (DLNM) along with quasi-poisson models based on a variation of the time-series design were applied to determine the potential impact of week-to-week solar activity level [represented by total interplanetary magnetic field strength (IMF)]] and geomagnetic activity level [represented by Kp index] on conceptions resulting in live births using Massachusetts Birth Registry 2000-2015 and identify the critical window of vulnerability. Factorized month variable and natural spline of year with 17 knots were included in the models to adjust for long-term trend and seasonal effect. We also investigated the association between same exposures and conceptions resulting in preterm birth within the same cohort. RESULTS:For IMF, we observed a non-linear exposure lag-response relationship during gestational weeks 13 to 35, with the strongest effect on live birth-identified conceptions (LBIC) occurs around week 25-30. During this window, per IQR increase in IMF level is associated with 0.4% decrease in LBIC. On the other hand, for Kp index, the non-linear exposure lag-response relationship were observed during gestational week 13 to 28. The strongest effect of Kp index on LBIC occurs around 18-23 and per IQR increase in Kp index is associated with 0.2% decrease in LBIC. We also identified non-linear positive relationships between exposures and preterm birth-identified conceptions (PBIC) during gestational weeks 20-30. CONCLUSIONS:Increased level of prenatal exposure to solar and geomagnetic activity were associated with decreased number of weekly live birth-identified conceptions as well as increased number of preterm birth-identified conceptions. Middle to late pregnancy appears to be window of vulnerability regarding these exposures. KEYWORDS: Solar activity, geomagnetic field, fetal growth, pregnancy, critical window, live birth bias