During the first few weeks of pregnancy, hCG levels usually double every 29-53 hours. They peak about 8-10 weeks after implantation, and then they slow down and level off, according to Dr. Brennan Lang, an Ob-Gyn at Baylor Obstetrics and Gynecology at Texas Children’s Pavilion for Women.
There’s a wide range of normal hCG levels, so high or low numbers aren’t usually cause for concern. In fact, up to 25% of healthy pregnancies don't have hormone levels that double every two days, says Michele Hakakha, M.D., an obstetrician and co-author of Expecting 411.
Even so, too-low numbers – or numbers that start dwindling or plateauing – may raise concerns. It’s possible that the doctor miscalculated your conception date, and your pregnancy isn’t as far along as previously thought. But you could also be suffering from blighted ovum, ectopic pregnancy, or a miscarriage.
Your doctor may perform a single hCG test at each prenatal appointment to make sure your first trimester is progressing properly. If hCG levels aren’t rising like they should – or if you’re experiencing symptoms of miscarriage – your Ob-Gyn may request that you take two hCG tests about 48 hours apart. Comparing the results will let her see trends in your hCG levels.
“During a miscarriage, hCG levels usually fall, plateau, or rise abnormally slow,” says Dr. Lang. He clarifies a “slow” rise as less than 35% over 48 hours. Any of these trends can signal miscarriage, but most of the time, “you have to wait until a pregnancy can be seen on ultrasound around six weeks to confirm things are going normally,” says Maureen Baldwin, M.D., MPH, an assistant professor of Obstetrics and Gynecology at Oregon Health & Science University.
Besides falling or plateauing hCG levels, other signs of miscarriage include:
After suffering from a miscarriage, your hCG levels will continue to decrease. They should return to normal in about 4-6 weeks, depending on how far along the pregnancy progressed. “After a miscarriage has been completed, there is not typically any need to monitor hCG levels,” says Dr. Baldwin. “If a home urine pregnancy test is still positive after a month, or if you still feel pregnant after a week, you should speak with your provider.”