We have just experienced a failed IVF. We had 25 eggs retrieved and 8 million sperm with average motility, yet none were able to fertilize the eggs. We are both in our early 30s and have endured eight years of fertility treatment. What are some possible causes of unfertilized eggs? Would another IVF make sense?

-- Andria

I would certainly consider another trial of IVF. Early studies showed that when no fertilization occurred on round one, at least 50 percent of couples had normal fertilization on the second go-around. Luckily things are even better now. But first let's consider why this might have occurred.

Fertilization requires sperm hyperactivation. As a sperm approaches the egg, its movement changes from straight-line swimming to a rapid circular motion. This drilling type of swimming pattern makes it easier for the sperm to pass through the outer cells surrounding the egg and ultimately through the outer protein layer or shell of the egg, called the zona pellucida. The sperm has a sac atop its head called an acrosomal membrane. As the sperm approaches the zona pellucida, the acrosomal membrane starts to leak enzymes that help soften the zona pellucida, allowing the sperm to penetrate the egg's outer surface. Once the sperm is through the outer protective layers, the egg becomes impenetrable, so that no other sperm can approach the inner egg membrane. Meanwhile, the egg engulfs the sperm and draws it inside. The sperm head is digested and the chromosomes prepare for cell division. While this is going on, the egg is finishing the process of meiosis (reducing its chromosome number from 46 to 23). Fertilization is complete when the fertilized egg divides. This is a very simplified description of egg fertilization; be assured that the process is quite a bit more complicated, and things can go wrong at just about every step.

So what do we do? I think it is important to review your case with your doctor to determine whether there was any evidence of correctable problems with either the sperm or egg that might interfere with a future attempt. Once any such issues are corrected, another cycle, this time using intracytoplasmic sperm injection (injecting a single sperm into each egg) would appear to be your best option. While ICSI does not solve all fertilization problems, in most cases, fertilization and embryo development will proceed normally.