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Sunday, 22 June 2014

ICSI: Intracytoplasmic sperm injection

Conventional IVF involves placement of motile sperms in close proximity of the eggs (oocytes). The sperms release enzymes that disperse the cumulus cells around the eggs and one of the sperms then penetrates the shell of the egg and the combination of egg and sperm leads to the formation of an embryo. When the motility of sperms is less or the number is insufficient, fertilisation may fail to occur. Intracytoplasmic Sperm Injection is the technique used to overcome this situation. ICSI is also required in cycles where PGD or PGS is employed as otherwise erroneous results may occur. 

The procedure is carried out in the embryology laboratory. Oocytes are normally surrounded by a thick fluffy cluster of cells (cumulus cells). In order to perform ICSI, the oocytes need to be denuded which means the cumulus cells need to be removed from around the oocytes by chemical or mechanical means. Denudation is essential for smooth and correct ICSI technique. Only mature eggs can be used for ICSI. The immature eggs cannot be used as these will form abnormal embryos.

The pregnancy rates and outcomes of cycles do not vary with the technique used for fertilisation (i.e., IVF versus ICSI). Embryo created are not superior to those produced after IVF and hence the decision to perform ICSI is based on the assessment of the couple and the embryologist's assessment of the semen parameters on the day of the egg collection. 

Sunday, 8 June 2014

Alternative trigger shot

Trigger shot is essentially to facilitate retrieval of eggs which up until the final maturation are attached with a stalk to the wall of the follicle. After trigger injection, the final maturation starts and the eggs complete their maturation division. Also the egg is released into the follicle fluid. Unless this happens, all the efforts of stimulation would be futile as lesser number or no eggs will be obtained at egg collection procedure. The traditional shot consists of hCG (or pregnancy hormone). The way it works has been explained in my previous post: IVF trigger shot.

What is the need for an alternative? It is the very real and very serious risk of OHSS (also discussed in a previous post: Is too much stimulation good?). In order to negate the risk of OHSS, an alternative trigger shot can be used. This is in the form of GnRH agonist. I have explained how agonists and antagonists work in my post: How is ovulation prevented in IVF?

The alternative trigger shot can only be used in antagonist cycles, in those women who are at risk of OHSS or those who are going through a egg donation cycle. Agonists 'trigger' a response from the pituitary in the form of release of a large amount of LH. This causes the final maturation in the follicles. As the life of LH is much shorter than hCG molecules, the risk of OHSS is very limited and short lasting with this protocol.

Women who have agonist as a trigger, should have a modified luteal phase support as otherwise the pregnancy rates are lower and miscarriage rates are higher. In my opinion, in the strife to eliminate OHSS, patients should be adequately counselled with respect to freezing of all embryos. My reason is that even if pregnancy occurs in these women, they are still at a risk of secondary OHSS which occurs from the pregnancy hormone released from the new pregnancy that has implanted. These symptoms will take much longer to abate in the background of an ongoing pregnancy!

Sunday, 1 June 2014

In vitro fertilisation

Once the eggs are collected, there are two methods of making embryos. The most common method is IVF. In vitro literally means in glass. So fertilisation that happens in petri dishes that were originally made of glass was termed in vitro fertilisation or IVF. The other method is called ICSI or Intra Cytoplasmic Sperm Injection which I will cover in the next post.

The eggs that are retrieved through aspiration of the follicle fluid are surrounded by a fluffy coat of small cells that surround and nourish the egg. These cells are called cumulus cells. These cells are also crucial for the maturation of the egg. In the natural cycles, the released egg is  surrounded by the cumulus cells. These cells are dispersed by the enzymes released from the head of the sperms (acrosome). This dispersal allows the sperms to reach the egg and one of the sperms is selected by nature to fertilise it.

The procedure is carried out on the same day as the egg collection and solution with specific concentration of motile sperms is added to the culture drops on the petri dish that contain the eggs. This mirrors what happens in nature. We rely on nature to certain extent to allow the best sperm to fertilize each of the eggs retrieved. It is generally recommended to fertilize eggs using this technique whenever possible. Next post on ICSI.....