The inability to conceive after a year of unprotected intercourse or the inability to carry a pregnancy to term. Generally speaking XXYs and variants typically produce zero sperm that would normally appear in a sperm test, but that does not mean that sperm is nonexistent. Recent medical fertility improvements include a testicular biopsy to work out the reason behind an absence of sperm cells (azoospermia), and is also used for testicular sperm extraction (TESE). Testicular sperm extraction coupled with in vitro fertilization can result in a full term pregnancy.
Further Reading and Resources:
Strategies for infertility treatment in Klinefelter Syndrome, an
abstract published by Göteborgs University.
The wife of an XXY, Wendy, writes an extremely timely and important letter about her family's successful odyssey to conceive a child.
Excellent infertility sites:
Resolve, a non-profit organization.
The International Council on Infertility Information Dissemination (INCIID)
Benchmark semen analysis and collection instructions.
A technical examination of Male Infertility
Another technical and very thorough examination of male infertility, including testes biopsy and ICSI, at the Center for Male Reproductive Medicine and Microsurgery, Cornell University.