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A1. I don't think the studies were that detailed to predict the probability of success at specific endometrial thicknesses. These studies were designed to determine the "breakpoint" thickness under which the chances of pregnancy were significantly reduced. 8mm was the breakpoint.

A2. The endometrial thckness is related to the amount estrogen given, but once there's enough in your sytem to facilitate maximum growth, taking more will not improve the thickness. An E2 in the 600's is more than enough to facilitate endometrial growth. However, the endometrium needs time to respond to the E2. That is why a couple of days in the stimulated cycle made a difference in the thickness. There is one other variable. Different people (nurses, techs, doctors) can measure the same lining and come up with different numbers. It is somewhat subjective. One person's 8 is another person's 9, etc.

We have had patients that had adequate linings on stimulated cycles, but less than optimal linings of FET's or donor cycles. When this happens, we cancel the cycle and then, on the next cycle, we stimulate the patient (as we would for an IUI/IVF cycle), but not give them hCG at the end. At the appropriate time, they start there progesterone. In many cases, the endometrium is adequate in the stimulated cycle for the FET or donor cycle using this approach.

You are correct that more diligent monitoring could have identified this problem earlier. Perhaps in time to cancel the cycle. Some programs even go so far as to have the patient go through a "mock" or "trial" cycle to determine if the endometrium will respond adequately to exogenous E2 (tablets, patches, injections, etc.). This also can prevent transferring embryos in a less than oprimal environment.

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Thank you for your replies. Do you have any idea what exactly "significantly reduced" chances amount to? And do you have any sense of why it would make a difference to recieve stimulation medications? Is the idea that the body reacts differently to endogenous estrogen than it does to exogenous estrogen?

The people at my clinic don't seem very concerned about the 7mm lining. They do about 400 IVFs per year, and they say they see pregnancies in the 6-10 mm range all the time. I don't know whether to find this reassuring or not.

Do you know at what point in the cycle your program begins the recipient on estrogen (and in what form it is given, if it matters)?

I want to say that I read your answer to the post regarding 3-day or 5-day transfer, and the fact that you easily admitted making a mistake gave me a great deal of confidence in you. In my experience people who really know what they are doing, and people who really care about the truth, find little problem in saying they were mistaken.

As always, thank you.

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The term "significant" in this context refers to statistical significance. Its a bit complicated to explain unless you have a background in statistics. The bottom line is that difference between the pregnancy rates when the endometrium was above or below 8mm was greater than expected from chance alone.

We have seen pregnancies from patients with 6mm endometriums too, but its not optimal and, more times than not, it doesn't work. The other thing to consider is that endometrial thickness measurements are somewhat subjective. Different people (doctors, techs, nurses) can measure the same endometrium and come up with different answers. One person's 6 is another person's 7, and so on.

We synchronize donor and recipient cycles with birth control pills. The recipient stops her pills 4 days before the donor, so that she gets her period first. The recipient then starts the estrogen patches (1X 0.1, then 2X 0.1, then 4X 0.1) so that she has 4 extra days for the endometrium to grow. Every program does things a little differently. There is no absolute right or wrong way to do this.

Yeah, well, what can I say. I goofed and I'm supposed to be an "expert". I'll check my facts to make sure I got it straight before posting next time.

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