Fertilization Failure

Fertilization can be defined as the union of oocyte and sperm, which are female and male reproductive cells, to form a single-celled zygote, which will form the embryo through subsequent cell divisions. Therefore, in order for fertilization to occur, the sperm must first reach the oocyte. This process occurs in the “in vitro” environment (in the woman’s uterus), where the sperm poured into the vagina after the man’s ejaculation during sexual intercourse first pass through the mucus-like cervix, which is the passage corridor to the uterus, and proceed in the uterus, reaching the oocyte that has been ovulated and waiting in the tubes, binding and changing its genetic structure within the sperm head. It occurs by transferring the nucleus containing DNA (DNA) and the cytoplasm containing many biomolecules that play a role in fertilization into the oocyte.

Fertilization Failure Treatment at Liv Hospital

Liv Hospital offers effective treatment options specifically tailored to couples who want to deal with fertilization failure. Expert teams evaluate the medical history and special conditions of couples and apply a wide range of reproductive health treatments. In vitro fertilization, genetic testing, hormone treatments, and a variety of other techniques are just a few of the approaches used in Liv Hospital’s fertilization failure treatment program. This comprehensive approach aims to provide couples with personalized and most effective treatment plans.

First Priority is for Sperm to Reach the Uterus

The first priority to ensure fertilization in the in vitro environment is that a sufficient number of motile sperm (~2 million) can reach the uterus. Secondly, sperm must be mature enough to have the necessary receptors and enzyme content in order to pass through the cumulus cell layer surrounding the oocyte in the part of the front of the head, called the acrosome, to bind to the zona pellucida layer, the outer protective sheath of the oocyte, and eventually to reach the oocyte. Various negativities that may occur during this process (low sperm count, tail defects affecting motility, acrosomal defects) may prevent fertilization from occurring.

Latest Technological Methods

The first priority in IVF treatments is to ensure that the sperm meets the oocyte directly, skipping the steps that may prevent the sperm from reaching the egg. For this purpose, IUI (Intra Uterine Insemination), IVF (In vitro Fertilization) or ICSI (Intra Cytoplasmic Sperm Injection) methods are applied to infertile couples, depending on the infertility status.

IUI Procedure

The purpose of the IUI process is; It is the delivery of motile sperm cells directly into the uterus by overcoming possible cervical problems that prevent sperm from reaching the uterus. Subsequent fertilization depends on the structural characteristics of the sperm and oocyte. In cases where IUI cannot be successful or results cannot be obtained with IUI due to predefined problems related to the gametes, fertilization methods are applied in the laboratory. For this purpose, IVF or ICSI is preferred, again in line with the indication of infertility.

Sperm Number and Quality is Important

Fertilization is achieved by keeping the sperm cells obtained through preliminary preparation procedures in the IVF process in the same culture environment with the oocytes obtained through the OPU (Oocyte Pick-up) process performed after the KOH (Controlled Ovarian Hyperstimulation) treatment applied to increase the number of oocytes. In order for this method to be applied, the number and quality of sperm must be sufficient (the number must be over 2 million/ml and there are no obvious morphological defects). Fertilization rates with IVF under favorable conditions are around 50-60 percent.

ICSI Method

Although the ICSI method is a preferred method, especially in couples with low sperm count, it is widely used because its fertilization success is higher (> 70 percent) than the IVF method. In this method, prepared sperm cells are selected under a microscope with the help of special micropipettes, using alternative selection methods preferred depending on their morphological characteristics, motility style and sperm structure, and are injected directly into the oocyte. In this way, other possible factors that may prevent sperm from reaching the oocyte are overcome. The ICSI method allows sperm to reach the oocyte directly; However, this does not mean that every oocyte will definitely be fertilized. Achieving fertilization requires the proper functioning of many stages at the molecular level, beyond the physical reaching of the sperm to the oocyte.

The first priority for the oocyte to be fertilized is that some factors in the sperm cytoplasm can activate the oocyte. The oocyte is a waiting cell in the metaphase 2 phase of meiosis and needs a stimulus from the sperm in order to continue dividing. At this point, the most prominent factor identified so far is a biomolecule called phospholipase-C. Phospholipase-C is the factor that initiates a series of processes in the oocyte cytoplasm that ultimately cause an increase in the intracellular calcium level and fluctuations that continue for a while. Meiosis of the oocyte that receives this signal continues and eventually a fertilized cell called zygote is formed.

The success rate of the ICSI method, which allows overcoming many obstacles that may affect fertilization, is around 70-80 percent; However, in some cases (3-5 percent) fertilization may not occur at all. The underlying causes of fertilization failure are quite complex and depend on many factors such as cycle-specific parameters, oocyte number and quality, and whether sperm number and quality are sufficient. Ultimately, the main reason for fertilization failure is the failure of oocyte activation. At this point, sperm defects take the lead.

Fertilization Failure

In order for normal fertilization to occur, the sperm must first have sufficient nuclear maturity and there must be no defects in the packaging of its genetic material. During the maturation process of the sperm, it is necessary for the tightly packaged DNA to transition to a looser packaged form in order to protect the genetic structure against environmental adverse effects during sperm production. Sperm morphological defect defined as globozoospermia is the most striking anomaly in this regard. In addition to the absence of acrosomes in sperm with this defect, the DNA remains tightly packed, which significantly affects fertilization success (0-20 percent). In addition, insufficiency of oocyte-activating factors in the sperm and defects in the organelle called centrioles, which form microtubule structures that manage the fertilization process, also negatively affect the success of fertilization.

The primary factor affecting the success of fertilization in the oocyte is the insufficient maturity of the oocyte cytoplasm (cytoplasmic maturation). The maturity of the oocyte is evaluated in two parts: nuclear and cytoplasmic. Although the observation of a cell called a polar body within the zona is a sign that the oocyte has reached nuclear maturity, an oocyte with this structure may not be at a sufficient level in terms of the amount of organelles (especially mitochondria) that will play an important role in the fertilization process, defined as cytoplasmic maturation. In this case, fertilization may not occur even if there is no problem with the sperm.

Alternative Methods

There are alternative methods that can be applied to overcome fertilization failure in the laboratory. The common point of these methods, defined as AOA (Assisted Oocyte Activation), is the artificial induction of intracellular calcium increase, which is the primary priority for fertilization of the oocyte. The methods used for this purpose are grouped under three headings: mechanical, electrical and chemical activation:

In the mechanical activation method, the aim is to increase the possibility of intra-oocyte calcium discharge by giving and receiving the oocyte cytoplasm several times with a micropipette during microinjection. Additionally, external administration of calcium into the oocyte during microinjection can also be applied. The chance of success is lower than other methods.

In the electrical activation method, low voltage electrical signals are given to microinjected oocytes using special devices and culture dishes for this method. It is aimed to widen the channels (pores) on the cell membrane and increase the entry of extracellular calcium into the cell.

In the chemical activation method, the aim is to expand the channels in the cell membrane by keeping the oocytes in various chemicals, just like in electrical activation. Ethanol, calcium ionophore A213187, ionomycin, puromycin, strontium chloride, phorbol ester and thimerosal can be given as examples of chemicals used for this purpose.

Although very successful results have been reported with oocyte activation, especially in sperm-related fertilization failures (fertilization rates of up to 100 percent can be achieved in cases of globozoospermia), it may not be possible to achieve the same success in oocyte-related cases. In this case, the most useful approach is to extend the waiting time until microinjection after OPU or to increase the probability of maturation of the oocytes obtained by manipulations during the KOH process (extending the time or trying different protocols), in line with the possibility that oocyte cytoplasmic maturation may be insufficient in cases of fertilization failure in previous attempts.