The outermost cells of an embryo make the hormone human chorionic gonadotropin, or hCG, to establish and maintain the pregnancy. A woman's blood or urine will only contain significant amounts of hCG when she is pregnant. In early pregnancy, levels of hCG should steadily increase, peaking at about the 12th week and then steadily declining. In early pregnancy, a single "low" measurement of hCG is not a cause for concern unless a later test indicates that the levels have not increased as expected.
Non-Pregnant
According to the American Association of Pregnancy, levels of hCG less than 5 mIU/ml indicate that a woman is not pregnant. Before menopause, a non-pregnant woman has hCG levels less than 5 mIU/ml. For women who have been through menopause, normal hCG levels are slightly higher but still below 9.5 mIU/ml.
Early Pregnancy
An hCG level over 25 mIU/ml indicates that a woman is pregnant. Even as early as 11 days after conception, or a few days before a missed period, doctors can measure this level of hCG in the blood. By 12 to 14 days after conception, a woman usually can measure hCG in the urine with a home pregnancy test kit.
The normal level of hCG for a given stage of pregnancy varies within a huge range. The American Association of Pregnancy provides a table of normal hCG levels throughout pregnancy. In a normal early pregnancy, levels of hCG double about every 48 to 72 hours. By the fifth week of pregnancy, a level of hCG less than 18 mIU/ml is outside of the normal range. By the sixth week, the low end of the range is 1,080 mIU/ml.
Later Pregnancy
As pregnancy progresses, the production of hCG slows and levels double approximately every 96 hours. In the ninth to 12th weeks, the low end of hCG levels lies at about 25,700 mIU/ml. By this point in pregnancy, a doctor can detect the fetal heartbeat with a stethoscope or see the fetus on ultrasound, so hCG levels assume less importance as a diagnostic tool.
Expected Increase
A single low measurement of hCG is not necessarily a concern. If a repeated test a few days later shows less of an increase than expected, that is more worrisome. In "Primary Care for Women," Dr. Phyllis Leppert and Dr. Jeffrey Peipert outline the minimal expected percentage increase in hCG levels in early pregnancy. Testing daily, hCG levels should increase at least 29 percent and using two-day intervals, hCG levels should increase at least 66 percent. Eighty-five percent of normal pregnancies fall within these guidelines, compared to only 13 percent of ectopic, or tubal, pregnancies.
Significance
A lower than expected level of hCG can mean that the pregnancy is not as far along as originally thought. Repeated low levels of hCG that fail to increase as expected can mean a miscarriage, a blighted ovum--a gestational sac with no embryo inside it--or an ectopic pregnancy.
References
- American Pregnancy Association: Human Chorionic Gonadotropin (hCG)
- "Primary Care for Women;" Phyllis Leppert and Jeffrey Peipert; 2004
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