Follicle size for IVF

Well, the very moment is coming, when eggs are ready to be extracted. How to determine this moment, you want to know? The primary sign, that indicates readiness degree of woman’s eggs, is follicle size.


The fact is that during the late luteal phase population of follicles with diameter 2-5 mm is formed; the dominant follicles will be selected for the next cycle. It is called ‘recruitment. Typically, we can talk about 3-11 follicles, but their number is reduced with age.

At the beginning of the menstrual cycle the largest follicles (5-10 mm) continue to develop, and the others regress. At 5-7 day one of the follicles 10 mm in size becomes dominant. The dominant follicle suppresses other ones. It becomes more on 2-3 mm daily and as a result reaches 17-27 mm. What is interesting, it is impossible to determine in advance what follicle will be dominant.

Before ovulation, follicle grows very quickly. It protrudes from the ovarian cortex, attains its border, and then explodes to release the egg and some antral fluid.


 Follicular monitoring

Follicular monitoring is used to track the state of follicles from late luteal phase to ovulation. To do this the follicle is assessed at regular intervals, and the result is recorded in the documents. Follicular monitoring is carried out by means of ultrasound diagnostics. The first measurements can be carried out on the third day of the cycle, their aim is to describe the features of the follicles (their quantity, shape and so on, everything, that is possible).

On the seventh day, we can begin to guess what follicle will be dominant and destined for ovulation. As a rule, there are three types of follicles competing for this role:

  1. Atretic dominant follicle.On the third day this follicle can be the largest, but it doesn’t mean it will lead to ovulation. Such follicle has rough edges and an irregular shape.
  2. Ovulatory dominant follicle. This follicle has smooth borders and round shape.
  3. Anovulatory-luteinizing dominant follicle. This type of dominant follicles grows quickly but fails to ovulate, and later turns to a cyst. These are smooth and round too.

As soon as one of the follicles reaches 16 mm size, specialists recommend a daily follicle monitoring. The next step is the detection of ovulation thanks to some signs.

Time to retrieve

Specialists say it’s very important to catch the moment when eggs will have ripe enough: in this case it’s just the time for egg retrieval when size at least 2 follicles is 18mm or greater, 50% or even more of all the follicles are at least 15mm in size and Estradiol levels are 1500-5000. These numbers refer to blood levels and measurements taken on the last day of stimulation, because, as a rule, nobody will take any blood on the day of retrieval.

Now, eggs must be retrieved, but they are not mature yet. To determine the moment when each follicle of 15mm or more produces a mature egg, doctor takes a final injection, that is called HCG.

For the first 36-40 hours after the HCG shot is taken, the larger eggs will go through their final maturation process. Full maturation of oocytes is a prerequisite, it’s a vital question: immature oocyte will not be fertilized. This is unacceptable to extract eggs prematurely. But also it must be done not more than 40 hours pass after the HCG shot, otherwise the egg is not fertilized too. The point is that ovulation can occur after 40 hours:  egg will come out from the ovary and appear in abdominal cavity; therefore, there will be nothing to retrieve. That is why it is so important that the last injection has been carried out according to the instructions. Optimal time is 36 hours. If you are late only on couple of hours, it’s not a disaster. But a longer delay can reduce the chances for success to zero.

So, an Egg Retrieval will be nearly in 36 hours following. This procedure implies minimal surgical intervention: a needle penetrates through the upper vaginal wall directly into the ovary and thus the eggs are retrieved. Depending on the number of follicles, this procedure can take from 20 to 45 minutes.

Is an Egg Retrieval painful? No, fortunately, it’s absolutely painless procedure. The only thin, after anesthesia mild drowsiness can remain.

The most interesting fact is that some follicles may be empty. In its turn, eggs from follicles 14 mm or less in size are often difficult to fertilize because they are immature. Then an embryologist studies the contents of all the follicles under the microscope and extracts eggs.


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