ERA Test for IVF: What Is It and When Should You Do It?
The ERA or Endometrial Receptivity Array has emerged as an important test for maximizing IVF success. When should IVF patients consider having it done?
What is the ERA test?
The ERA or endometrial receptivity array is a test used to determine whether a frozen embryo is being transferred at the correct time. The uterus needs two hormones to prepare for implantation.
Which hormones needed to prepare the uterus for implantation?
The first hormone, estrogen, works to thicken the uterine lining. The length of time that a woman takes estrogen does not seem to be important. Whether longer or shorter, the chance for pregnancy doesn't seem to change - as long as the lining gets thick enough.
The second hormone, progesterone, causes changes in the uterine lining that allow an embryo to implant. These changes don't occur immediately, however. It takes several days before the uterine lining develops the capacity for allowing an embryo to implant.
The importance of timing and the "Window of Implantation"
The uterus only maintains this ability for a short time. This is known as the "window of implantation". If an embryo is placed into the uterus before or after the window of implantation, it has a lower ability to implant and produce a pregnancy. Stated another way for an embryo transfer - Timing is Everything!
How is the ERA test performed?
Doctors will have their patients perform a "mock cycle". In a mock cycle, women take the same medications that she would take during a transfer cycle: estrogen followed by progesterone.
Then, instead of doing a transfer, the doctor takes a small sample of the uterine lining. This is called an "endometrial biopsy". The testing is done on this sample.
What do the results of the ERA mean?
When the results are received, they will indicate that the timing was correct, this is called "Receptive" or that the timing was incorrect, which is called "Non-receptive" The non-receptives can be further divided into two groups:
"Pre-Receptive" means that the lining needs more time before it is ready. "Post-Receptive" means that the lining was already past the time of maximal receptivity and therefore needs to be shortened.
If the results are pre or post receptive, the testing lab will also give a recommendation for how to change it.
How do you correct a uterine lining that is "Non-Receptive"?
For example, if the biopsy was performed 125 hours after progesterone was started and was "Pre-Receptive", the recommendation might be to perform it 24 hours later at 149 hours.
For most women, the window of implantation occurs on the sixth day of progesterone.
When should women consider having the ERA test?
Couples who have never failed an embryo transfer have a low chance for finding an abnormal result. Somewhere around 5 to 10%. In other words, more than 90% of the time, couples without any previous failures will not benefit from doing the test.
Studies tell us that couples who have failed to achieve pregnancy after multiple attempts at embryo transfer, with high quality embryos, have a higher chance for continued failure with additional attempts.
The first group that might benefit from an ERA are those that have had multiple failures. Studies show that in couples with multiple failures, about one third will have an abnormal test.
Couples with a non-receptive result that don't make any changes to the timing, will have a lower chance for success if they try another embryo transfer.
Another group that seems to have a higher chance for an abnormal result are women who are obese. Fertility doctors designate patients with obesity as those women with a BMI or body mass index over 30. Women with a BMI over 30 have the same rate of abnormal results as couples with multiple failures. Women with a BMI over 40 have an even higher rate of abnormal test results.
One group of patients that I get asked about frequently are those with early miscarriage. In this group, implantation of the embryo occurred, but there was a miscarriage in the first several days before a pregnancy could be seen on ultrasound. Some people thought that this could be the result of placing the embryo at a less than optimal time outside the peak window of implantation. However, the studies so far do not show a benefit of using the ERA in this group.
Our bottom line
Women with multiple failures should consider having an ERA before their next transfer and women with a high BMI should consider having the ERA before their first transfer. The ERA is designed to benefit couples who have not had first-time IVF success.