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    Geographic variation in the incidence of hypertension in pregnancy.

    World Health Organization [WHO]. International Collaborative Study of Hypertensive Disorders of Pregnancy


    The Maternal and Child Health Unit of the World Health Organization undertook a series of prospective studies in the early 1980s in Burma, China, Thailand, and Viet Nam to determine how much variation in the incidence of hypertensive disorders of pregnancy there was and how much of it reflected differences in baseline blood pressures. Pregnant women in 3 urban and 2 rural centers in Burma, a part of the city of Shanghai, 1 urban and 1 rural center in Thailand, and 1 urban and 2 rural centers in Viet Nam were enrolled. Each mother was given a card recording weight, signs of edema, proteinuria, and blood pressure with diastolic pressure based on the 4th Korotkoff sound. Gestation was calculated from the 1st day of the last menstrual period, and all the women were primigravidas. There was wide variation in the distribution of highest diastolic pressure before the onset of labor. The proportion of mothers whose diastolic pressure was greater than 89 mm mercury at any time during pregnancy varied from 33% in China to 26% in Thailand, 7% in Burma, and 5% in Viet Nam. There as very little variation in the numbers of mothers with proteinuria. China had the lowest rate of eclampsia but the highest prevalence of hypertensive disorders, presumably because preeclampsia was treated. Hypertensive disorders were diagnosed among 31% of Chinese women, 5% of Burmese women, and 1% of women in Viet Nam and Thailand. Blood pressure measurements were analyzed for each country by week of gestation, and the mean diastolic pressure in the 2nd trimester was constant across all 4 populations; the difference between the lowest and highest was only 3.5 mm mercury. Thereafter the differences increased, with the greatest increases in China and Thailand and very little increase in Burma and Viet Nam. The differences thus appear to be racial, but whether they are genetically or environmentally caused remains to be determined.
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