Seasonal variation in pre-eclamptic rate and its association with the ambient temperature and humidity in early pregnancy.
OBJECTIVE
To determine any relationship between ambient temperatures adjusted for humidity at conception and the occurrence of pre-eclampsia.


METHODS
The subjects were singleton primiparae delivered in a Teaching Hospital between 1995 and 2002. We studied the odds of developing pre-eclampsia across months and investigated the association between the pre-eclamptic rates based on the months of conception and the mean monthly heat index.


RESULTS
A total of 245 (1.6%) women were diagnosed pre-eclampsia and eclampsia during the study period. There was a significant association between the seasons of conception and rate of pre-eclampsia (logistic regression Wald chi(2) = 9.2, p = 0.03). Conceptions during summer had a higher risk of pre-eclampsia than those during autumn (2.3 vs. 1.6%, OR 1.7, 95% CI 1.2-2.5). Women who conceived in June had the highest risk of developing pre-eclampsia (OR 2.8, 95% CI 1.5-5.2) while women who conceived in October had the lowest after adjusting for age. A 2-month time lag was observed between the peak pre-eclamptic rate in women who conceived in June and the peak heat index in August.


CONCLUSIONS
Singleton primiparous women who conceived in summer and had a longer exposure to higher ambient temperature were at a greater risk of pre-eclampsia.
Tam
Wing Hung
WH
Department of Obstetrics and Gynecology, The Chinese University of Hong Kong, Hong Kong, SAR, China. tamwh@cuhk.edu.hk
Sahota
Daljit S
DS
Lau
Tze Kin
TK
Li
Chi Yin
CY
Fung
Tak Yuen
TY
D000328:Adult; D002681:China / Q000453:epidemiology; D005260:Female; D005306:Fertilization; D006801:Humans; D006813:Humidity; D015994:Incidence; D011225:Pre-Eclampsia / Q000453:epidemiology*; D011247:Pregnancy; D012307:Risk Factors; D012621:Seasons; D013696:Temperature; D013997:Time Factors