The time between the hCG and retrieval For an FSH injection cycle leading to insemination, it’s ok if the ovulation naturally occurs a little early (via a premature LH surge) because we can just do the insemination early. Rarely it’s too early, before the follicle is big enough, and we cancel the cycle. However, for an IVF cycle we have to cancel the cycle if there is an early natural LH surge, even if it’s only a little early, because the timing of the retrieval is very dependent on when the surge starts. The retrieval needs to be about 34-36 hours past the start of the surge (which would also be the time if the hCG shot).
Because we are not taking blood every hour, if the blood test shows a rise in the LH level, we don’t really know when the rise started so we don’t know the right time for retrieval. Lupron, Antagon and Cetrotide prevent the natural rise of the LH, so the premature surge usually cannot occur. However, these drugs do not interfere with the effects of an hCG injection. So there is no natural surge, but there is an artificial surge which starts the moment the hCG goes in.
Final Maturation There is a second very important job of the LH Surge/hCG injectionit causes the egg to mature. As the days of stimulation progress the eggs are slowly maturing, but more is needed for the final maturation. Necessary last minute changes occur inside the egg from the LH/ hCG.
Why is this important? An immature egg will not fertilize. If the retrieval is before about 33 hours after the hCG, the result will be immature eggs. Sometimes they are all immature, or just some.
If the retrieval is 38-39 hours after the hCG, the eggs will be mature but they will already have ovulated. We would retrieve none; they would be floating in the pelvis around the ovaries waiting to get picked up by the tubes. So we need to grab the eggs just after they mature but just before they ovulate, which is at about 34-37 hours after the hCG injection.
What day should you get your hCG? hCG can only mature eggs that have been growing for enough time for the follicle to become large. The sizes of all of the follicles need to be taken into consideration before giving hCG in IVF cycle.
Not all of the follicles grow at the same rate. For example, if there are 10 follicles, and the biggest is 18mm, they will not all be 18 mm. Some will be mid-sized and some will be much smaller. Each follicle does not need to be 18 mm to produce an egg that is mature. As long as the biggest (the lead follicle) is 17-18mm, the mid-sized (13-16) should also have mature eggs. The small follicles (10-12) may or not be mature. But if the lead follicle is 14 mm, none of the eggs have yet reached maturity. Giving hCG would not be enough to achieve maturity.
How Important are Estrogen Levels? Not very. When you are monitored for your IVF cycle, the follicle size is much more important that the estrogen (estradiol) levels. We need the estrogen to rise, but if midway through your cycle we see 10 follicles, with the biggest being 13 mm, we don’t really care if the estrogen level is 500 or 900. Estrogen is more important when we are monitoring someone who may be on track for hyperstimulation.
Therefore, we use mostly the size of the follicles, with not much emphasis on the estradiol levels, to determine when to give the hCG. At NYU we feel the best time to get the hCG is when the lead follicle reaches 18 mm. Now because there are many variations from cycle to cycle and from patient to patient, it’s not easy to say that 18 mm is the rule.
For example, let’s say there is one follicle 18 mm, three that are 15 mm and others that are smaller. Here we may worry that some of the small ones may be too immature, so we may wait another day before giving the hCG. Let’s say there are 20 follicles, with the biggest 17mm and an estrogen level of 2900. Here we are aware that the smaller follicles may be immature, but we also are concerned about the estradiol getting much higher because the woman would be increasing her risk of hyperstimulation. So we give the hCG at 17 mm, which may yield some immature eggs, but should give us enough mature eggs to work with.
And there are many more variations. Some women have gotten their hCG a little on the early side and have all mature eggs. Some women in their first cycle get the hCG at 18 mm with lots of good size follicles, and have ½ their eggs be immature. So next cycle we wait till the follicles are 20-22 mm before giving hCG. This sometimes gets more mature eggs but sometimes no matter what we do, that woman’s ovaries make more immature eggs than expected.
So why not wait and give hCG later? Because eggs can get over-mature. This over-maturity can lead to lower embryo quality and lower pregnancy rates.
When we see the records of women who have failed IVF elsewhere, many times we see that he hCG was given with large sized follicles. The first and easiest “fix” we can do is to give the hCG earlier in her next cycle, more inline with our standard procedures.
Why do some doctors wait longer to give the hCG? Some may feel that the higher the estradiol level the better, so by waiting estrogen levels will go up. This is probably not important. Others may feel that it is necessary to wait so there will be no immature eggs. Well this sounds good, but it may not be worth sacrificing the quality of the eggs form larger follicles, which are probably the best eggs anyway.
And back to the original question. What if instead of the average 11-12 days it takes to grow the follicles, they are of the right size after only 6 days or 8 days? If the size is good, but it seems early, we usually go at least one more day that we normally would, maybe 2. If it’s day 9 and the follicles are 19-20 mm, it really sounds ok to give hCG. If it’s day 7 (so 5-6 days of FSH injections), and the follicles are 17-18 mm, more time would probably be a good idea.
Thanks for reading and don’t forget the disclaimer 5/17/06.