Special to The Washington Post KIDNEY DISEASE For the tiniest babies, chronic kidney problems loom largest. THE QUESTION The kidneys of babies who are unusually small at birth might not have developed fully in the womb. Could a person's size at birth, then, increase the likelihood of developing chronic kidney disease later in life? THIS STUDY analyzed data from 18 studies, involving more than 2.2 million people. Those who weighed less than 5 1/2 pounds at birth had about a 70 percent greater risk for developing kidney disease as adults than did people who were born at a normal weight. WHO MAY BE AFFECTED? People whose weight at birth was considered low. Experts suggest that people with an increased risk for kidney disease should have their blood, urine and blood pressure checked periodically for signs of the disease and should avoid medications that could harm the kidneys. CAVEATS The authors indicated that little information was available on lifestyle factors, including smoking and socioeconomic status, which have been shown to affect risk for kidney disease. The average age at which the presence of kidney disease was assessed varied widely among the studies. FIND THIS STUDY August issue of the American Journal of Kidney Diseases. LEARN MORE ABOUT kidney disease at www.nkdep.nih.gov and www.kidney.org. The research described in Quick Study comes from credible, peer-reviewed journals. Nonetheless, conclusive evidence about a treatment's effectiveness is rarely found in a single study. Anyone considering changing or beginning treatment of any kind should consult with a physician. 