Human chorionic gonadotropin hormone (HCG), also known as beta human chorionic gonadotropin (b-HCG), is one of the most talked-about hormones of pregnancy. We asked Michele Hakakha, M.D., an obstetrician and co-author of Expecting 411, and Elisa Ross, M.D., an ob-gyn at Cleveland Clinic's Hillcrest Hospital, to explain HCG levels and give a thorough explanation of why this hormone is so important during your pregnancy.
Q: What is HCG?
A: HCG is a hormone made by the placenta. HCG levels surge in the first trimester of pregnancy and is detectable in your urine within a day or two of implantation -- so when you pee on a home pregnancy test you're actually measuring your HCG levels. "What makes HCG so interesting is that there is a huge range of what's normal when it comes to this number," says Dr. Hakakha. In normal pregnancies, she notes, it's likely that there is a such a wide range because different women have different placentas, each with different functional abilities.
Q: What patterns do HCG levels maintain during pregnancy?
A: Although most hormones increase at the beginning of pregnancy and continue to rise throughout the 40-week journey, HCG is different. From the time your baby is conceived until 10 weeks of gestation, your HCG levels rise rapidly, doubling every two to three days, but then the levels begin to fall. "This means that at the beginning, your number might be two. It'll then move to four, eight, and 16, and then it really picks up speed, moving into the 25,000 to 50,000 range," says Dr. Ross. "When it gets to 100,000, it turns around and goes down again. For the rest of your pregnancy, your HCG level will likely remain at 10,000."
Q: Why do HCG levels fluctuate so much?
A: The answer is complex. Most experts theorize that the reason for change in HCG levels is that--at a certain point in the pregnancy--the placenta takes over making the hormones estrogen and progesterone. This means HCG is no longer needed to stimulate the ovary to make hormones, says Dr. Ross. Again, it's at the beginning of your pregnancy that your HCG levels are especially crucial. Those levels help your doctor determine whether or not your pregnancy is a healthy one. But keep in mind that even if you're bleeding at the beginning of pregnancy, it's a healthy pregnancy if your HCG number doubles.
Q: What can my doctor tell from my HCG levels?
A: Because the normal range is so great, it's often hard to tell much about a pregnancy from just one HCG measurement, according to Dr. Hakakha. Doctors can, however, can gain information from looking at trends. A normal pregnancy has HCG levels that double every 48 hours. Although there are exceptions, HCG levels that rise at a lower rate, and then plateau or even decline, often indicate an abnormally developing pregnancy or an ectopic pregnancy, one that exists outside of the uterus.
Q: Can my doctor tell whether or not I'm having twins from my HCG levels?
A: Yes. Two or more babies means two or more placentas. Each placenta makes its own HCG, so more babies means higher levels of this hormone.
Q: Is HCG causing my morning sickness?
A: "We believe that HCG stimulates an area in the brain that triggers nausea. This makes a woman very sensitive to smells and tastes," says Dr. Hakakha. Historically, this would serve a pregnant woman well. Anything that smelled or tasted bad (and could therefore be dangerous to her unborn child) would trigger the nausea reflex, steering a woman away from that particular food. But we also see that once HCG levels plateau, nausea and vomiting taper off--usually after the 14th week of pregnancy. That said, HCG might not be the only culprit resposible for morning sickness - estrogen may also play a role.
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