The Real Meaning of Beta hCG Levels

13 Jul
Beta hCG Pregnancy Test

Certainly the most anticipated lab test in a fertility clinic is a human chorionic gonadotropin (hCG) level. While everyone knows that having a positive beta hCG is the ultimate prize, it is far more difficult to truly understand what the test is really telling you.

First, what does a positive (+) beta hCG test really mean? Here we must differentiate between a urine test and a blood pregnancy test. The only real difference is the sensitivity of the test, meaning how high does the hCG level actually have to be to get detected. On a home pregnancy test, the lowest level routinely detected varies between 20-30 mIU/ml. As these levels are achieved fairly early in pregnancy – in fact by the time the expected period is missed – the levels should be above this detection level.

A blood test, on the other hand, is a more vigorous tool and can detect hCG very accurately as low as 5 mIU/ml. Levels below 5 can be detected, but the accuracy of these evaluations suffers greatly. These levels can be detected even before the missed period, hence their usage in IVF cycles. One thing that must be understood here is that these tests cannot distinguish between hCG created by the pregnancy or that given by injection. One must therefore be careful interpreting levels that have been drawn close to the time of the hCG trigger of ovulation/maturity. Twelve days is generally enough time to allow what was injected to be completely metabolized and cleared.

Second, how high must the beta hCG level be before we can actually expect to see something on ultrasound? Once upon a time, when the world was young and I was fresh out of training, we did primarily abdominal scanning. The hCG level most commensurate with seeing the pregnancy was very high, about 6500 mIU/ml. Since the advent of the trans vaginal probe and the great increase in the ability to see things in the uterus, this “U/S detectable” level decreases to about 1000 mIU/ml. This can be equated to about 6 weeks gestation (remember, we always add two weeks to go all the way back to the start of the cycle, not from the time of implantation).

Beta hCG Levels

The hardest question to answer is how fast these levels should increase. A common rule of thumb is that on average they should approximately double every two days. But remember that these are averages. When following such numbers, we must use curves like the one shown above. The only truly abnormal parts of the curve are the upper 2.5% and the lower 2.5%. All the other values strung between these two points are still normal, they are simply more or less than their neighbor. It is the same with hCG levels. If the number is not doubling, that is not a reason to “hang crepe” and panic. It is still most probably normal.

Additionally, the doubling time (time needed for the value to double) also changes as the pregnancy advances, hence you can expect the increase to slow down as you follow it. In fact, once the thresholds for ultrasound detection have been passed, following serial hCG levels does little except overly worry people. Again if I had a nickel for every baby I have held in my arms that did not initially have perfectly doubling hCG levels or for every D & C I have had to perform for a failed pregnancy that was indeed doubling, I would be retired in the South of France reading poetry and eating peeled grapes. At a bottom line, do not hesitate to ask your coordinator or physician about their ideas concerning these levels so you do not unduly worry yourselves.

1,053 Comments

  • Jessica says:

    I had a tubal reversal June 14th 2013. After 10 months I finally got my positive. Tuesday I had a very faint positive and called my Dr for a blood test to be sure. That was 15 dpo. my levels that day which was taken about 4:30pm were at 6.8. I then had quite a bit of bleeding on and off since Wednesday. Even still today (Monday) but its really dark and not much. I did another blood test Friday at 18 dpo at about 11am ish. Those levels were 12.2. Have been taking home PG test all weekend and all still very positive and getting darker. But she doesn’t want to do anymore blood test for a whole week. She did put me on 200 mg of progesterone today. Says it can’t hurt but could help. Does it sound like I will be ok with those numbers?

  • Lina says:

    I have had several chemical pregnancies this year. My betas this cycle are: 29 on 11dpo, 109 on 13dpo (25 hr doubling time), and 166 on 15dpo (79 hr doubling time). My last beta is worrisome- does it look like I’m heading toward another chemical?

    • Geoffrey Sher says:

      Hi Lena,

      The recurrent nature of your very early pregnancy losses is indeed concerning. If this pregnancy goes the same way…then you really need to be thoroughly re-evaluated as to cause. Such an evaluation done against the backdrop of your age and your husband’s sperm quality should include the protocol(s) used for ovarian stimulation and also of those factors that play an important role in implantation (anatomical and immunologic).

      Please go to the home page of this blog, http://www.IVFauthority.com . When you get there look for a “search bar” in the upper right hand column. Then type in the following subjects into the bar, click and this will take you to all the relevant articles I posted there.
      1. “An Individualized Approach to Ovarian stimulation” (posted on November 22nd, 2010)

      2. Ovarian Stimulation for IVF: The most important determinant of IVF Outcome” (Nov. 2103)

      3. “Agonist/Antagonist Conversion Protocol”

      4. “Immunologic Implantation Dysfunction” (posted on May, 10th and on May 16th respectively.

      5. “Thyroid Autoimmune Disease and IVF”

      6. “Embryo Implantation………” (Part-1 and Part- 2—-Posted August 2012)

      7. “Traveling for IVF from Out of State/Country– The Process at SIRM-Las Vegas” (posted on March, 21st 2012)

      8.“A personalized, stepwise approach to IVF at SIRM”; Parts 1 & 2 (posted March, 2012)

      9. “IVF success: Factors that influence outcome”

      10. “Use of the Birth Control Pill in IVF”

      Consider calling 800-780-7437 or 702-699-7437 to arrange a Skype with me so we can discuss your case in detail.

      Finally, perhaps you would be interested in accessing my new book (recently released). It is the 4th edition (and a re-write) of “In Vitro Fertilization, the ART of Making Babies”. The book is available through “Amazon.com” as a down-load or in book form. It can also be obtained from most bookstores.

      Geoff Sher

      P.S: Please go to http://www.youtube.com/watch?v=Vp3GYuqn2eM&feature=youtu.be
      To view a video-tutorial by Linda Vignapiano RN, Clinical Manager at SIRM-Las Vegas.

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