You’ve talked to your fertility provider and decided intrauterine insemination (IUI) is the right choice for you. Great!
By this point, we generally have a sperm count. This can be divided into two parts: The initial sample and the washed sample.
We like to see sperm in the “normal” range. This is because normal sperm, as you know, are able to enter eggs on their own. Fertilization is a very likely outcome.
The capacity to enter eggs is based on the “acrosome reaction”. While we’re not able to measure this capacity directly, we can use indirect measurements like concentration, motility, and morphology.
A normal range sperm sample will have a concentration over 20 million/mL, motility over 40% or 50%, and morphology over 5%. If your sperm are below these numbers in any one of those parameters, it reduces the chances that any individual sperm will be able to enter an egg.
The process of washing involves putting the sperm in a Centrifuge. The sperm will form a pellet at the bottom of the tube. We discard the seminal fluid and place a layer of special culture medium on top of the sperm. This allows us to separate the functional sperm – which “swim up” into the medium – and leave the less motile sperm behind. This may be repeated a few times until we end up with a smaller number of high-quality sperm with a motility of at least 80%.
We routinely see motility rates in the 90% or 95% range. One reason your sample may be less is if the technician had to “dive deep” to find any sperm at all.
If you’ve selected frozen-thawed sperm, you may see significantly reduced motility rates. We find 60% – 70% motility is common with donor sperm. While it’s not uncommon to see numbers as low as 30% or 40%, we ask the sperm banks to provide a new sample when we see numbers in that range.
Reduced motility usually means the sperm have a reduced capacity for entering eggs.
Why don’t we add samples together?
Adding three or four donor sperm packets together doesn’t actually provide any extra value. The sperm have the same concentration, motility and morphology levels. This is a case where more does not equal better.
After all, when a couple have intercourse, only 60 thousand sperm enter the uterus. With IUI, there’s a much higher number than that. So your odds on volume are already increased.
The key isn’t really about the number, but the quality of the sperm. The more normal the sperm appears, the more likely it is that they’re able to enter eggs on their own.