by Fred Licciardi, M.D.
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 MaturationThere is a second very important job of the LH Surge/hCG injection:
it
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.
Recent Comments