What does it mean if the hCG level is increasing but not doubling in early pregnancy? Is this a sign of miscarriage?
In about 85% of normal pregnancies, the level of the pregnancy hormone hCG (human chorionic gonadotropin) will double every two to three days during early pregnancy. When the hCG levels are increasing but not doubling at least every 3 days, this may be a warning sign of problems -- but not necessarily. In one study that monitored hCG increase patterns in early pregnancy, the lowest documented 2-day hCG increase in a normal pregnancy was 53%. This might mean that an hCG level that increased by about 75% after three days could theoretically be normal.
So if your hCG levels are increasing but not quite doubling, your doctor might continue to monitor your pregnancy, but it's too early to say that the levels are a sign of miscarriage. Remember too that the rate of hCG doubling slows down as the pregnancy progresses, so slower hCG doubling times are normal if you're past the first weeks of pregnancy. By the second half of the first trimester, ultrasound is more reliable than hCG levels for judging whether a pregnancy is viable.
Note that if your hCG level is decreasing in early pregnancy, this is unfortunately a reliable sign of miscarriage. An hCG level that doesn't increase considerably (even if not double) over two to three days in early pregnancy most likely means miscarriage as well, but your doctor will give you more information on what to expect.
Barnhart, Kurt T. MD, MSCE; Sammel, Mary D. ScD; Rinaudo, Paolo F. MD, PhD; Zhou, Lan PhD; Hummel, Amy C. CCRC; Guo, Wensheng PhD. "Symptomatic Patients With an Early Viable Intrauterine Pregnancy: hCG Curves Redefined." Obstetrics & Gynecology: July 2004 - Volume 104 - Issue 1 - pp 50-55.
Human Chorionic Gonadotropin (hCG) - The Pregnancy Hormone. American Pregnancy Association. Accessed: Apr 5, 2010. http://www.americanpregnancy.org/duringpregnancy/hcglevels.html