Geographic variation in the incidence of hypertension in pregnancy. World Health Organization International Collaborative Study of Hypertensive Disorders of Pregnancy.

Prospectively collected information on blood pressure and proteinuria was available for geographically defined populations of primigravidas in Burma, China, Thailand, and Viet Nam. Clinically recognized hypertension during pregnancy varied by a factor of 25 between countries, and even a strict definition of proteinuric preeclampsia revealed a variation by a factor of 5. Serial measurements of blood pressure in each country showed remarkably similar levels early in the second trimester but a divergence thereafter. We conclude that there are genuine differences in the incidence of hypertensive disorders of pregnancy in the populations of Southeast Asia and that these are not caused by underlying differences in the baseline blood pressures in these populations.