Three Cheers for Y-chromosome Bearing Sperm

From Science Blog:

More boys than girls born in U.S. -- again

For the 63rd year in a row, the number of boys born in the United States outnumbers births of girls – in 2002 94,232 more boys than girls were born. This is the central finding of a new Centers for Disease Control and Prevention (CDC) report that examines total sex ratios at birth for over six decades. The total sex ratio is the number of male births divided by female births times 1,000.

I wonder if anyone has taken a close look to see what causes this sex ratio distortion. It seems to me it could occur any time from spermatogenesis to birth. There could be segregation distortion during meiosis, differences in sperm success, effects on implantation in the uterus, or developmental differences.

By the way, to learn more about human fertilization check out this movie by Planned Parenthood (via Pharyngula).