How Miscarriage Affects HCG Levels

The Human Chorionic Gonadotropin is a hormone that both men and women possess in their bodies.  Studies have connected it with fertility, but for women, this hormone is more prevalent and increases at conception and throughout the stages of pregnancy due to production by the placenta.  Its purpose is to first send messages to the endometrium to prepare for the fertilized egg and during pregnancy, it acts as protection for the developing baby.

The levels of HCG vary widely from person to person since everyone’s body is different.  Thus, even for women the levels can differ during and after pregnancy depending on their chemical make-up.  With that in mind, the unfortunate event of a miscarriage can wreak havoc on the levels of this hormone, sometimes even weeks or months later.  So open and consistent communication with an obstetrician/gynecologist along with attention to one’s overall feeling of well-being is vital, especially if a couple wishes to attempt conception again.

So one may ask what happens to the HCG levels at the beginning of pregnancy, and when do the numbers signal a miscarriage?  Immediately at conception the levels rise and continue to double every 48 to 72 hours for the first four weeks of pregnancy.  At about six or seven weeks, they might reach 1200 mIU/ml (milli-international units per milliliter).  (Again, this can vary.) At this point, the HCG levels take a bit longer to double sometimes three and half days, give or take.  They tend to peak at about eight to eleven weeks and of course, drop off after the baby is delivered in the case of a full term pregnancy.  While remembering that one blood test that indicates low levels does not necessarily point toward miscarriage, an extremely slow increase, a significant drop, or no increase at all during the first trimester usually relates to a complication or loss of the pregnancy.  (Doctors will often order two or more blood tests just to be sure.)  In particular, when one blood test shows an HCG level that is significantly lower than a previous test, then the physician will order additional tests in one to two days to ascertain whether or not levels are still declining.  If levels are still not doubling, if not still decreasing, then this would indicate that a miscarriage has occurred.

To give a better idea of “normal” HCG levels throughout the course of a pregnancy, the following shows number of weeks of gestation in relation to how many mIU/ml:

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  • Three weeks: 5 to 50 mIU/ml
  • Five weeks: 18 to 17,340 mIU/ml
  • Seven to eight weeks: 76,590 to 229,000 mIU/ml
  • Nine to twelve weeks: 25,700 to 288,000 mIU/ml
  • Thirteen to sixteen weeks: 13,300 to 254,000 mIU/ml
  • Seventeen to twenty-four weeks: 4060 to 165,400 mIU/ml
  • Twenty-five to forty weeks: 3640 to 117,000 mIU/ml

These ranges are based from the time of the last missed menstrual cycle.  So, as one can see levels do plateau right about the third trimester; therefore the first trimester is really the time to keep an eye on HCG ranges.  Most doctors, oftentimes, rely more on ultrasound during the latter stages of pregnancy anyway.  However, if during the first trimester, blood tests indicate a change in levels that do not show the normal doubling, if not a significant decrease, a healthcare provider needs to be notified right away if any one or more of the following symptoms are exhibited:

  • Vaginal bleeding
  • Abdominal cramping that accompanies bleeding or spotting
  • Passing tissue from the vagina

Once a miscarriage has occurred, understanding when HCG levels will drop to zero can be a challenge—again because the rate of decrease varies among woman along with the symptoms that accompany this physiological change.  The length of time depends the most on high the HCG levels were at the time of the miscarriage.  Therefore, if the miscarriage happens very early on in the first trimester, then the HCG level will drop to zero much more rapidly; whereas when the loss of pregnancy occurs in the second or even early in the third trimester, the level takes even more time to decline. Typically, according to the American Association for Clinical Chemistry, it takes nine to thirty-five days (an average of nineteen days) for the HCG to become undetectable.  Regardless, doctors often order quantitative blood tests to monitor the amount of HCG while caring for women who have suffered a miscarriage.  The reason for this is to take extra caution in case HCG levels do not become undetectable and thus, to rule out the possibility of the presence of any HCG-producing material.  If this happens, then the material would be to be removed as soon as possible.

Similarly, in the case of an ectopic pregnancy, alarmingly low levels of the hormone would be detected, and after treatment is administered, then levels would have to be continuously monitored.  In either case, keeping watch over the HCG levels, physical symptoms, and emotional well-being will help in the recovery process, especially if a couple wishes to attempt to conceive again.

Another important reason for being mindful of the HCG levels and following the doctor’s orders after a miscarriage is that normally, a provider will advise to wait another six to eight weeks before attempting to conceive, which is the standard waiting time after a major medical event like this one.  If the hormone levels are back to zero, this could indicate that the uterine lining is back to its original condition and ready for the implantation of another fertilized egg.  Moreover, if HCG levels are still elevated slightly, then a normal menstrual cycle may not occur for another one to two months and longer in a few cases.  (If a period does not arrive in two months or more, a woman should contact her healthcare provider.)  Also, waiting for HCG levels to drop before trying to conceive ensures that an accurate lab result will be obtained, thus avoiding a “false positive” gained through an over-the-counter home pregnancy test.

Although HCG levels may have dropped dramatically in the weeks that follow, a certain amount can show up on a urine test, which can lead to the false positive reading when a couple tries too soon to conceive.  Worse yet, a continual drop in the hormone’s level during the course of weekly lab testing could give the false impression of another miscarriage.  In a similar scenario, if attempting too soon after, considering the changes the woman’s body undergoes after a miscarriage, she might still exhibit some of the physical symptoms.  As a result, a healthcare provider would have to consider monitoring through regular blood testing and eventually ultrasound anyway just to be certain of what exactly is going on—another pregnancy or continued recovery after the previous miscarriage.  All in all, waiting for at least six to eight weeks, if not longer, is the safest choice.

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