Testing for pregnancy after an embryo transfer in an IVF cycle
Posted Jan 05 2011 10:04pm
While all IVF patients understand with their heads that not every IVF cycle results in success, in their heart of hearts, every patient expects to get pregnant every time they do IVF ! This is why the 2ww after the embryo transfer can be so nerve-wracking ! Am I pregnant or not ? Have the embryos implanted or not ? The suspense during the 2ww can be even worse than the pain of the IVF injections !
Most patients would love to have a test which will allow them to find out if they are pregnant immediately after the embryo transfer ! Have the embryos stuck or not ? Why can’t we do a pregnancy test and find out right now ? Even if I am not pregnant, at least it’s better to know than to be unsure.
To understand why patients ( and their doctors ) still have to suffer through a 2 week wait to find out the outcome of an IVF cycle, let’s look at the biological basis of pregnancy tests and how they work.
A pregnancy test measures the amount of beta hCG ( human chorionic gonadotropin) that is in your body. HCG is a hormone which is produced by the trophectoderm cells of the embryo. It is produced in detectable quantities only after the embryo implants. Since implantation occurs 3 - 8 days after the embryo transfer ( depending upon whether you have had a Day 3 transfer or a blastocyst transfer), this means that the HCG produced by your embryo will be first detectable in your bloodstream only after this time.
As your pregnancy progresses, the amount of hCG in your system will increase. At 10 days past ovulation ( DPO) , for example, the average woman has an hCG measurement of around 25 mIU. This amount doubles to 50 mIU at 12 days past ovulation, and then doubles again to 100 mIU at around two weeks past ovulation. Every woman’s body is different, and there’s a lot of variation in HCG levels from woman to woman !
Home pregnancy tests measure the level of HCG in urine. Different pregnancy tests have different levels of sensitivity which means if you use a home pregnancy test that is sensitive to 100 mIU, it will not tell you that you are pregnant if your level of hCG is only 75 mIU. These tests cannot measure a level lower than 25, so they do not become accurate until a few days after embryo implantation. A negative result before then is meaningless, since there would not be a high enough level of HCG to detect even if you were pregnant. If your test is negative, you should retest after 2 days. This is why taking a pregnancy test too early can lead to inaccurate results. I know it’s hard to wait those extra days and you may want to try much earlier. It’s fine to do this, but please don’t assume that a negative results means that you are not pregnant. This is also why blood tests for HCG are much better than urine tests. Not only are they more reliable, accurate and sensitive, they also give the doctor a number which he can measure and monitor.
If blood tests are so sensitive, then why not do a blood test for HCG 1 week after the embryo transfer ? Unfortunately, doing a blood test for HCG so soon does not make any sense. This is because there will still be some HCG in your body as a result of the HCG trigger shot ( Choragon or Ovidrel) which the doctor gave you to trigger off ovulation 36 hours prior to egg collection. If you test too early, the test will always be positive, as this HCG will show up in the test and give rise to false hopes ! This is why the doctor needs to repeat the blood test for HCG after 48-72 hours. In a healthy pregnancy, the HCG levels will continue to rise. If they do not do so, this means this is not a viable pregnancy.
Finally, remember that you should do the test even if you bleed. Bleeding can sometimes occur during pregnancy as well – and just because you have had bleeding or spotting does not mean you are not pregnant !