Washington ? Good news for the nation’s babies: Nearly 90 percent of newborns are getting tested for a host of rare but devastating genetic disorders.

Since 2004, specialists have urged that every U.S. newborn be checked for 29 conditions, to detect the few thousand who will need early treatment to avoid death, retardation or other serious problems.

The federal government hasn’t issued national screening guidelines, but more states are following the advice on their own. As of June 1, 40 states required testing for more than 20 of those disorders, according to a March of Dimes report issued today.

Topping the list are 13 states plus Washington, D.C., that required testing of every newborn for the entire list of 29 conditions, which range from sickle cell anemia and cystic fibrosis to lesser-known diseases such as the metabolic disorder LCHAD.

New Hampshire also began testing for all 29 conditions on July 1, after the report’s deadline.

The report marks steady progress: Just 38 percent of babies were born in states with intensive screening when the March of Dimes counted in 2005, and 64 percent last year. This year, that number rises to 87.5 percent of newborns, or about 3.6 million babies, the child advocacy group calculated.

Still, almost half a million infants are born in states that require testing for 12 or fewer of the conditions, the analysis found. They include Arkansas, Massachusetts, Nebraska, Oklahoma, Pennsylvania and Washington.

Three more – Kansas, Montana and West Virginia – passed legislation this year requiring checks for all 29 disorders, but that expanded testing hasn’t yet begun.

While some states tout testing for even more conditions, the 29 on this “core list” – hearing loss plus 28 genetic diseases that can be diagnosed using a single drop of blood – are those deemed most important for screening by the American College of Medical Genetics.