During an IVF cycle, there are three things you want to know after every office visit; follicle size, the thickness of your uterine lining, and your estradiol level. These are the key data that let you and your doctor know how your cycle is progressing.

Follicle Size and Follicle Count

IVF is all about the eggs and one important indicator of your cycle is follicle size. Follicle size indicates how your eggs are developing and when they will be mature enough for retrieval. Follicles grow approximately two millimeters a day and size is an average. Thus a follicle that is ten by twelve millimeters averages to eleven millimeters. While every clinic is different, the trigger shot of HCG (given right before egg retrieval) is administered around the eighteen to twenty millimeter mark.

It is important to realize, though, that follicles don't grow unless estradiol levels are just right. Estradiol levels, more than any other factor can derail an invitro fertilization cycle.

Uterine Lining Thickness

In-vitro patients undergo multiple ultrasound appointments and blood draws to gather data about how their cycle is progressing. The ultrasound technician will count the number of follicles, measure follicle size as well as the thickness of the uterine lining. A thicker lining is better, but thinner linings may not necessarily be a problem.

Uterine lining should measure at least 7 to 8 mm in thickness. Progesterone given toward the end of the IVF cycle will assist in thickening the uterine lining. Estradiol levels also affect the uterine lining, with higher levels correlating to a thicker uterine lining.

Estradiol Levels During In-Vitro Fertilization

Just like Goldilocks' porridge, the estradiol level during an IVF cycle needs to be just right. Too high, you're at risk for hyperstimulation. Too low, your response to your doctor's protocol may not be optimal. But what exactly is a good, low, or high estradiol level? How can you judge the progress of an in-vitro fertilization cycle by the estradiol levels?

It's difficult to give exact numbers because every cycle and body is different, but, in general, a 'good' estradiol level is between 150- 500 pg/ml on day eight of an IVF cycle. Approximate doubling of the day eight value every 48 hours is a positive sign of continued follicle development.

High Estradiol Levels

As for high estradiol levels, anything over 3000 is considered high and at risk for hyperstimulation (also referred to as Ovarian Hyperstimulation Syndrome or OHSS). Because hyperstimulation can be serious, yourfertility treatment center may reduce the dosage on your medications and 'coast' until the levels come down. If levels remain high, the cycle could be canceled due to the risk to your health as well as the fact that coasting for too long can reduce egg quality.

Low Estradiol Levels

Low estradiol levels aren't necessarily better. According to a 2004 study published in the Journal of Assisted Reproduction and Genetics, levels lower than 75 pg/ml were predictive of cycle cancellation.

What to Do When Estradiol Levels Are Too High or Too Low

What can you do as a patient? Know your estradiol level and your clinic's cutoffs for high and low levels. If your estradiol appears to be low or high, ask your doctor to reevaluate your protocol and consider coasting to see if estradiol levels even out. Be sure to discuss the benefits and risks of moving forward as well, especially with regards to Ovarian Hyperstimulation Syndrome and the risk of pregnancy multiples.


If you decide to coast to see if the E2 (estradiol) levels come down, be aware that coasting can negatively affect egg quality. Be sure to discuss any changes to your protocol thoroughly with your doctor and prepare for the possibility of cancellation, particularly if the estradiol levels continue to rise despite coasting.

In terms of preventing pregnancy multiples and the mom-to-be's health, cancellation may be the safest course, but that doesn't make it a happy occasion. However, keep in mind that even failed cycles yield important data that may be pivotal in achieving a future pregnancy. All is not lost if an in-vitro cycle is canceled. Be gentle with yourself if a cycle is cancelled and don't stop believing in a positive outcome.