Redefining [beta]-HCG in viable pregnancies: rose 50% every 2 days.

SAN ANTONIO -- Serial [beta]-HCG levels rose at a minimum of only 50% every 2 days in a study of 293 viable first-trimester pregnancies, contradicting the widely held belief that levels should rise at least 66%.

"This should hopefully change our clinical care. We were overestimating how fast a pregnancy should grow in the past, and this shows that we should be more conservative and not intervene so quickly," Dr. Kurt Barnhart said at the annual meeting of the American Society for Reproductive Medicine.

"We found that instead of rising by 66% every 2 [days], [beta]-HCG levels in viable pregnancies can rise by as little as 50% every 2 days. Under the old rule, if the levels rose less than 66%, people theoretically would have said it was nonviable, whereas these new rules are saying ...