Sperm Sorter Sets Gender
Some parents-to-be hope for a girl. Some wish for a boy. The outcome, however, has always been pretty much a matter of chance--until now.
Researchers at the Genetics & IVF Institute in Fairfax, Va., recently announced a technique that helps stack the odds in favor of parents getting what they want.
Using a mechanical sperm sorter, the Fairfax team reported that nearly 93 percent of the babies born were of the desired sex.
All the couples in this study wanted girls. However, the technique also can easily help those who desire a boy. Will such technology lead to a United States overpopulated by one sex? Most ethicists don't think that will happen any time soon. Nonetheless, the new technology raises some concerns about the future, they say.
Before getting to the ethical debate about sex selection, consider the research itself. Reproductive biologist Edward F. Fugger and his colleagues at the Genetics & IVF Institute began their study by recruiting 119 couples who wanted a baby girl.
In most cases, the couples already had a boy or boys, and they wanted a girl for variety-to balance their family, as the scientists say. In a few cases, couples faced the risk of giving birth to a child with a genetic disorder that strikes boys only.
The patented sperm sorter used by Fugger and his team helps parents pick out the child's gender before fertilization of the egg.
The technology, developed during animal studies by Lawrence A. Johnson of the U.S. Department of Agriculture in Beltsville, Md., exploits the difference in amounts of DNA in X and Y chromosomes. Sperm bearing the X, or female, chromosome have more DNA than sperm carrying the Y, or male, chromosome.
An embryo resulting from the merger of an egg, which always carries an X chromosome, and a sperm carrying an X chromosome will have two Xs and, therefore, develop into a girl. An egg fertilized by a sperm carrying a Y chromosome becomes a boy.
In the September issue of Human Reproduction, Fugger and his colleagues describe their use of the method. Each couple provided a sperm sample, which the researchers treated with a dye that attaches to DNA and glows under laser light. The team then exposed the tagged sperm to a laser beam.
The researchers reasoned that the X-carrying sperm would glow the brightest under the laser light. Sure enough, even though sperm carrying an X chromosome-and 22 other chromosomes-contain only 2.8 percent more DNA than those bearing a Y, the sorter separated the bright sperm from the dim sperm. It then directed most of those bearing X chromosomes to swim down one collection tube, and most of the Y-bearing sperm went down another tube.
When the researchers analyzed the sperm in the X collection tube, they found that 85 percent had the X chromosome, as desired. The researchers thus estimate that samples from the X collection tubes are five to six times as likely to result in a girl baby than in a boy.
In 92 cases, the researchers inseted the sorted sperm directly into the woman's uterus, a procedure called intrauterine insemination. In this version of artificial insemination, the sperm must latch onto and fertilize an egg in the woman's body for pregnancy to occur.
Some of the couples required more complex-and expensive-techniques to achieve pregnancy. In 27 cases, the researchers united sperm and egg in a laboratory dish and then transferred the resulting embryos to the woman's uterus.
Out of 119 women, 29 got pregnant using the sorted sperm. In 8 women, the pregnancy ended in miscarriage or surgery, the latter because of a dangerous condition in which the fertilized egg starts to grow in a fallopian tube above the uterus.
At the time the Fairfax researchers published their journal article, 12 women had ongoing pregnancies and 9 women had already delivered 11 babies, including two sets of twins. As of mid-November, Fugger and his colleagues had not released updated results.
Of the 14 pregnancies in which the gender of the child had been determined, 13 were girls, the researchers say.
Fugger and his team are also conducting a study with parents who want boys. In such cases, the sperm sorter is less effective at concentrating Y-bearing sperm. Still, the method yields a sperm sample in which 65 percent carry the Y chromosome, Fugger says. The team has not announced any results of that study yet.
The researchers identified no safety concerns in the published study. "All of the babies born have been healthy," Fugger says. "That doesn't mean that all of the risk has been excluded. There's a lot that's not known."
By Kathleen Fackelmann