What’s the Deal with hCG?

Beta hCG is often referred to as the “pregnancy hormone,” because at any given time when it is detected in the blood – a woman is considered pregnant. Of course there are other less common clinical scenarios in which beta hCG is found in the blood, but that’s out of the range of this blog. Most commonly when this hormone is found in the blood it is an indication of pregnancy after implantation takes place.

An individual beta hCG level usually does not mean much – it’s the pattern of change (hopefully rise) that predicts whether the pregnancy is likely to be normal. Traditionally, in a normal pregnancy the beta hCG doubles every 48-72 hours. The truth is that a rise of at least 53% can still be consistent with a normal pregnancy.

There are several different scenarios that can play out once beta hCG is detected in the blood:

  1. The beta hCG falls – this pregnancy is termed “biochemical,” meaning that implantation took place and the hCG was in the system, but the embryo stopped growing before anything could ever be seen on ultrasound.
  2. The beta hCG rises appropriately – hopefully this is a normal pregnancy, and once the hCG reaches a threshold level (usually ~1,500-2,000) an early pregnancy sac can be seen in the uterus via ultrasound.
  3. The beta hCG rises, but not appropriately – these are the pregnancies I worry most about. The rise in b-hCG indicates that there is pregnancy tissue secreting the hormone, but it’s not producing enough (a sign that it is abnormal). Most often when this occurs the pregnancy is in the uterus where it should be, but it just is not developing normally. A more worrisome situation, but thankfully less common, is something called an ectopic pregnancy.

In scenario #3, although it is more common for the abnormally rising beta hCG to indicate an abnormal intrauterine pregnancy, the bigger concern is an ectopic pregnancy. The definition of an ectopic pregnancy is any pregnancy that implants outside of the uterus. Most commonly ectopics are seen in the fallopian tube, but it could be elsewhere. An ectopic pregnancy will never be a normal pregnancy because for one reason or another it decided to develop in a location that is not suitable to sustain a pregnancy for 10 months. The earlier an ectopic pregnancy is detected, the better. There are medical and surgical treatments options when the ectopic is found early, but when an ectopic is discovered late it may result in bleeding from the fallopian tube, or even rupture of that tube with resultant internal bleeding.

This is why doctors always suspect an abnormally rising beta to be an ectopic – because missing that diagnosis can be catastrophic.

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