Infertility often involves challenges with sperm quality, particularly morphology, or the sperm’s shape. Couples pursuing assisted reproductive technology frequently encounter sperm washing or preparation. This process is a prerequisite for many treatments and aims to optimize the semen sample for fertilization. The central question for many patients is whether this laboratory intervention can physically correct or improve the shape of their sperm.
Assessing Sperm Quality and Morphology
Sperm morphology refers to the size, appearance, and structure of the sperm cells, including the head, midpiece, and tail. The shape of the sperm is a factor in its ability to swim correctly and to penetrate and fertilize an egg. Abnormal morphology, termed teratozoospermia, occurs when a high percentage of sperm deviates from the ideal shape.
Assessment is typically done in a laboratory using specific criteria, most notably the Kruger strict criteria, incorporated into the World Health Organization’s guidelines. These criteria are highly rigorous, defining a normal sperm as having a smooth, oval head and an absence of defects in the neck, midpiece, or tail. Under these strict standards, a sample is considered to have normal morphology even if only 4% or more of the sperm meet all the criteria. Evaluating morphology helps predict the potential success of fertilization, though it is only one component alongside sperm count and motility.
The Process of Sperm Preparation
Sperm preparation, commonly called sperm washing, is a laboratory technique performed on a semen sample before it is used in fertility treatments. The primary goals of this procedure are not directly related to shape correction. Instead, the process focuses on separating the sperm cells from the seminal plasma, which contains substances like prostaglandins that can cause severe uterine cramping if introduced during procedures like Intrauterine Insemination (IUI). The washing also removes debris, non-motile cells, and white blood cells that can interfere with fertilization or cause oxidative stress.
The two most common techniques used are density gradient centrifugation and the swim-up method. Density gradient centrifugation involves spinning the sample through layers of liquid with varying densities, which allows the denser, healthier, and more motile sperm to travel to the bottom layer. The swim-up method relies on the active movement of the most motile sperm to swim from the semen pellet into an overlying culture medium.
Washing’s Impact: Selection, Not Correction
The answer to whether sperm washing improves morphology is that it does not physically reshape an individual sperm cell. Morphology is an intrinsic characteristic of the sperm, determined during its development; a misshapen sperm cannot be corrected by washing. The laboratory techniques are highly effective at selecting the best available sperm, which often results in a final, processed sample that shows a higher percentage of normal morphology. This apparent improvement is a result of filtration, not transformation.
The methods, particularly density gradient centrifugation, select for sperm with better motility and density, characteristics that are frequently correlated with normal morphology and better DNA integrity. The process filters out the non-motile and less viable sperm, which are often the ones with severe morphological defects. If a sample contains very few normally shaped sperm to begin with, the washing process cannot create more, but it will ensure that the few healthy ones are concentrated for use.
Application in Assisted Reproductive Technology
The purified, concentrated sample of motile sperm is immediately ready for use in various assisted reproductive technology procedures. For Intrauterine Insemination (IUI), the washed sperm are placed directly into the woman’s uterus, bypassing the cervix and increasing the number of motile sperm reaching the fallopian tubes.
In In Vitro Fertilization (IVF) and Intracytoplasmic Sperm Injection (ICSI), sperm preparation is also a necessary initial step. For standard IVF, the purified sample is placed with the eggs in a dish to allow natural fertilization to occur. During ICSI, a single, morphologically sound, and viable sperm is selected from the washed sample and directly injected into the egg. This careful selection and preparation maximizes the chances of successful fertilization and implantation by delivering the highest quality sperm available for the procedure.