Seasonal variation in pregnancy hypertension is correlated with sunlight intensity.
OBJECTIVE
To examine seasonality of pregnancy hypertension rates, and whether they related to sunlight levels around conception.


METHODS
Data were obtained for 424,732 singleton pregnancies conceived from 2001 through 2005 in Australia. We analyzed monthly rates of pregnancy hypertension and preeclampsia in relation to monthly solar radiation.


RESULTS
Pregnancy hypertension rates, by month of conception, were lowest in autumn (7.3%) and highest in spring (8.9%). Higher sunlight intensity before delivery, but not around conception, was associated with decreased pregnancy hypertension (r = -0.67). Increased sunlight around conception may correlate with decreased rates of early-onset preeclampsia (r = -0.51; P = .09).


CONCLUSIONS
The correlation between sunlight after conception and pregnancy hypertension was opposite to that hypothesized; however, sunlight levels before delivery did correlate with lower hypertension rates. For sunlight or ambient temperature to explain seasonal variation, the plausible exposure window is the period before delivery, but this may not apply to early-onset preeclampsia.
Kolling Institute, University of Sydney, New South Wales, Australia.
Charles S
CS
Algert
Christine L
CL
Roberts
Antonia W
AW
Shand
Jonathan M
JM
Morris
Jane B
JB
Ford
D001315:Australia / Q000453:epidemiology; D036861:Delivery, Obstetric; D005260:Female; D005306:Fertilization; D006801:Humans; D046110:Hypertension, Pregnancy-Induced / Q000453:epidemiology*; D011247:Pregnancy; D012621:Seasons; D013472:Sunlight