"If you identify a Y chromosome, you can make a pretty good guess that it's a male, but for a female it's more difficult," Lockwood said. Also, fetal cells from previous pregnancies can continue to circulate and confuse the results.
Early-detection capabilities also raise complicated ethical issues, such as the potential increase in gender-selective abortions, experts noted.
For example, Lockwood said, "a disproportionate number of female fetuses have been terminated worldwide, and a 2-to-1 male-to-female ratio could lead to social unrest and wars."
In other words, does the ability to buy pink or blue clothing and room decorations early outweigh the potential for selective terminations?
Another important issue to consider is that all pregnancies naturally carry a 20 percent miscarriage rate, said Dr. Henry Klapholz, chairman of obestrics and gynecology at MetroWest Medical Center in Framingham, Mass., and a professor at Harvard Medical School.
"At five weeks, quite frankly, you don't know if a pregnancy is 'good,'" Klapholz said. "It's bad enough to think you're going to have a baby because of a positive pregnancy test. Now couples will imagine a baby, then the gender of baby, then the name of the baby -- this could be potentially more devastating than a miscarriage."
"I always tell my patients, don't plan on a pregnancy until you have a fetal heartbeat; otherwise, the outcome could be terribly disappointing," Klapholz continued." To test so early would be unwise."