Semen Prep for Fertilzation

Providing a Semen Sample

During the IVF process, the male partner usually provides a fresh semen sample on the day of the egg retrieval.

Occasionally, one or more semen samples are frozen, in advance, for use on the day of the egg retrieval. This is done for one of three reasons; if there is a possibility that the male partner may not be available on the day of the egg retrieval, if the male partner has a very low sperm count and needs to bank several samples in order to accomplish fertilization, or if the male partner feels significant anxiety about collecting a semen sample on the day of egg retrieval.

A third option that couples may employ is the use of frozen semen samples from a donor.

Processing the Sperm

Regardless of the source of the sperm, there are similarities in the method of processing it and in its use once the process is completed.

The first thing that the embryologist must do with a semen sample is an analysis in order to determine the number and the quality of the sperm in the sample. The semen analysis will reveal the concentration, the number of motile sperm and the number of normal sperm. This initial determination will dictate the treatment of the sample and the eventual method that will be used to try to accomplish fertilization of the eggs.

If the sperm are present in high numbers and the motility (movement) and the morphology (shape) are each in normal range, insemination will be used to accomplish fertilization of the eggs. Even if there is a high number of good quality sperm, insemination may not be used to achieve fertilization when the following conditions exist; the presence of anti-sperm antibodies, a previous IVF case with poor fertilization, a previous case with high abnormal fertilization, the male partner having had a vas reversal or a if a low number of eggs has been retrieved (5 or fewer) during the current egg retrieval. In these special cases, ICSI will be required to fertilize the eggs.

If the sample has an abnormally low number of sperm, a low percent of either motile sperm or morphologically normal sperm, ICSI will be used to accomplish fertilization. As mentioned above, ICSI will also be used in those circumstances such as; anti-sperm antibodies, previous IVF cases with poor fertilization, high abnormal fertilization, vas reversal or when a low number of eggs have been retrieved.

Semen samples are prepared in a manner that will yield a population of sperm that are highly motile, have a high percent of normal morphology and have a fast forward movement or progression. This is accomplished by centrifuging the semen sample through a column of silica beads that act as a filter. The beads trap most of the sperm that are not moving or those sperm that have an abnormal shape.

When there is a low number of quality sperm in the initial semen sample, there will not be enough quality sperm in the sample after the prep to accomplish fertilization by using insemination.

The goal in insemination in the IVF lab is to provide 15,000 to 30,000 motile normal sperm to place in each drop of medium that will contain one or two eggs. When the percent of motile or normal sperm after prep is low, a greater number of sperm must be used in each drop in order to have the right number of motile, normal sperm available to fertilize the eggs.

For example, if there are 6 million sperm in the final prep but only 50% are moving and only 50% have a normal shape, then there are actually only 1.5 million sperm that are moving and normal. If the insemination number is determined to be 15,000 motile, normal sperm in each drop containing eggs, the math dictates that the embryologist should place one hundredth of the volume of the final prep volume in order to yield 15,000 sperm that are both moving and normal. However, in order to provide 15,000 “good” sperm, the embryologist has to place a total of 60,000 sperm in each drop. This high number of actual sperm in the drop with the eggs can be harmful in two ways. First, sperm are living cells that use the medium and put off waste products. In the insemination process, sperm and eggs are together for 18 hours. This large number of sperm will degenerate the conditions in the drop so as to make it a poor environment for the eggs. Secondly, sperm have an enzyme in the front portion of their head that assists them in entering the egg. The large amount of enzyme from 60,000 sperm will destroy the outer shells of the eggs and prevent their development into embryos.

So, when the motility and/or morphology are low, the preferred method of achieving fertilization is ICSI. This method will allow for fertilization with a poor semen sample without exposing the eggs to a poor quality environment for 18 hours.

If ICSI is so effective, why isn’t it used exclusively to fertilize eggs? ICSI remains an invasive procedure in which a glass micro needle is inserted into the cell material of the egg. Since the inner membrane is penetrated, it is a fact that some eggs will not survive the procedure. For this reason, ICSI is only used when it is believed to be the best way to maximize fertilization and embryo development.