Miscarriage tests men should have . . .

Your partner must not be left out of the evaluation. Sperm might be slippery liuttle swimmers but they shouldn't escape responsibility for what needs to follow!

To begin with, he should have a blood test for a karyotype, to look for a balanced chromosomal translocation. But there are more specialized tests that can be done on the semen.

When sperm are formed (in the process called spermiogenesis, which transforms a round cell into one with the profile of a cruise missile, see WebPage 3), the DNA gets tightly packed, like a warhead. To do this, the chains of DNA in the chromosomes need to form super coils, which involves breaking the chains and reforming them. After the sperm fertilizes the egg this process has to be un-done (and results in the chromosomes forming the male pronucleus). Almost always, probably, some DNA breaks are left over that the egg has to repair as best it can.

If there's too much DNA damage in the sperm head it swamps the egg's ability to repair it. As a result, the embryo won't form properly. It doesn't under cleavage, or it fails to undergo implantation, or it may go on to miscarry.

There is a test available at Sydney IVF to measure DNA breakage in sperm, the sperm chromatin structure assay, developed at the State University of South Dakota by Dr Don Evenson. If the proportion of sperm cells in the sperm count showing DNA damage is more than 15% then subfertility or miscarriage are more likely. More than 30% of sperm cells damaged is likely to cause sterility or recurrent miscarriage. This is a useful addition to just having a careful sperm count done (though this is important also ... with "strict criteria" used for normality.

The second structural feature the fertilizing sperm endows to the embryo is the centriole, a minute rod-shaped structure at the head-end of the sperm's tail filament, or flagellum. After fertilization the centriole replicates, forming the two poles that the chromosomes are oriented towards in the cell divisions of mitosis. Faults in the centriole mean faults in cell division, and faults in cell division mean faults in the embryo's constitution.

Whether disorders of the centriole can cause miscarriage is not certain: most defects are probably so catastrophic that cleavage and implantation fail. Sperm affected may show increased breaks of the tail or abnormalities of the sperm mid-piece on careful semen analysis.

. . . and polymorphisms to watch out for

And finally, many causes of miscarriage are genetic, especially if both potential parents are heterozygous for a genetic polymorphism that, in homozygous form, makes the embryo especially vulnerable. These are discussed in the main text.

Polymorphisms differ from "mutations" by being much commoner in the population, and by frequently showing some kind of advantage in certain circumstances (called heterozygous advantage), which promotes their inheritance.

Examples relevant to recurrent miscarriage include may include HLA-G*01013 (which decreases the amount of soluble HLA-G soaking the mother's immune system, possibly reducing tolerance) and the gene for folic acid metabolism, MTHFR, abnormalities of which affect the sperm count (in a way that can be overcome by mega-supplements of 5 milligrams of folic acid a day).