Human Chorionic Gonadotropin (HCG) is a hormone uniquely produced during pregnancy. It is initially secreted by specialized cells surrounding the developing embryo, which later form the placenta. HCG’s primary function in early pregnancy is to signal the body about the pregnancy and support the corpus luteum, a temporary structure in the ovary. The corpus luteum, in turn, produces progesterone, a hormone essential for thickening the uterine lining and maintaining the pregnancy. HCG also tells the body to stop menstruating.
The Expected HCG Level Progression
In a healthy pregnancy, HCG levels exhibit a predictable pattern of increase, peak, and then decline. After conception, HCG levels rise rapidly, doubling every 48 to 72 hours during the first 8 to 11 weeks of pregnancy. This rapid increase indicates that the pregnancy is progressing as expected. Healthcare providers may monitor this doubling time in early pregnancy if there are concerns about viability.
HCG levels reach their highest concentration between 8 and 12 weeks of gestation. Following this peak, the levels begin to decrease and then stabilize at a lower level for the remainder of the pregnancy. This decline occurs because the placenta develops sufficiently to take over the production of essential hormones like progesterone and estrogen. Once the placenta is mature and functioning, high levels of HCG are no longer needed to stimulate the corpus luteum, leading to the drop.
Reasons for Concerning HCG Declines
A common reason for a concerning drop in HCG levels is a miscarriage, the loss of a pregnancy before 20 weeks of gestation. In such cases, HCG levels fail to rise as expected or begin to decrease. After a miscarriage, HCG levels will fall, returning to pre-pregnancy levels within 7 to 60 days, depending on how far along the pregnancy was.
An ectopic pregnancy, where the fertilized egg implants outside the uterus, most commonly in a fallopian tube, can also be associated with abnormal HCG patterns. In an ectopic pregnancy, HCG levels may rise more slowly than in a healthy pregnancy, or they might plateau or even drop erratically. This abnormal rise in HCG, combined with ultrasound findings, helps healthcare providers diagnose this potentially life-threatening condition.
A chemical pregnancy is another scenario where HCG levels rise briefly and then fall rapidly. This refers to a very early miscarriage where a fertilized egg implants enough to produce HCG, but then fails to develop further. HCG levels decrease as the embryo stops developing.
A blighted ovum, also known as an anembryonic pregnancy, is a type of early miscarriage where a fertilized egg implants and a gestational sac develops, but an embryo never forms. The body still produces HCG because the gestational sac and placenta-forming tissues are present. Eventually, HCG levels will decline. Lower-than-expected or dropping HCG levels can indicate a blighted ovum, though ultrasound is necessary for definitive diagnosis.
Responding to a Drop in HCG Levels
If a drop in HCG levels is observed, it is important to consult a healthcare professional. A single HCG measurement is not sufficient for diagnosis, as levels can vary widely among individuals and between different pregnancies for the same person. Instead, healthcare providers look at the trend of HCG levels over time.
The next steps often involve a series of repeat HCG blood tests, usually taken 48 to 72 hours apart, to assess whether the levels are rising, plateauing, or declining. An ultrasound examination is also used in conjunction with HCG levels. An ultrasound can help determine the location of the pregnancy, confirm the presence or absence of a gestational sac or embryo, and assess the pregnancy’s development.
These evaluations help determine the cause of the HCG decline and guide medical management. Low or declining HCG levels are a symptom of an underlying issue, not a cause. While nothing can be done to directly increase HCG levels, identifying the reason for the drop allows for medical intervention and support.