US centre offers choice over sex of babyBMJ 1998; 317 doi: https://doi.org/10.1136/bmj.317.7161.768 (Published 19 September 1998) Cite this as: BMJ 1998;317:768
A commercial genetics and infertility centre in the United States is offering customers the option of predetermining the sex of their offspring through the Microsort technique of sperm selection. The procedure has raised both ethical and safety concerns.
Doctors at the Genetics and In Vitro Fertilization Institute in Virginia have modified a sperm sorting system originally developed by researchers at the Department of Agriculture and used in breeding farm animals (Human Reproduction 1998:13:367-70). The technique relies on detecting differences in the quantity of DNA between sperm carrying the X chromosome and those bearing the Y chromosome.
X chromosomes characteristically carry more genetic material than their Y counterparts. In humans this difference in DNA quantity is a mere 2.8% (in cows it is up to 4.1%). This difference is exploited by labelling the sperm with a DNA fluorescent dye, bisbenzimide, and then sorting them by laser spectrophotometry. The labelled sperm are placed in a flow cytometer and exposed to ultraviolet light. Those sperm carrying the X chromosome emit more light than those carrying the Y chromosome and can be separated out.
The researchers report an 85% success rate in the enrichment procedure for the X chromosome, but only a 65% success rate for the Y chromosome. So far, the team has tried the technique on 119 patients a total of 233 times. Most of these patients requested the procedure for “family balancing,” to ensure the production of a girl when most of the previous children were boys. In some cases, a medical justification for selecting female offspring, such as the avoidance of X linked diseases, was given.
With intrauterine insemination, the procedure resulted in 29 pregnancies, of which 12 are ongoing, eight have failed, and nine have resulted in 11 births. The researchers report that, of the offspring and of six of the fetuses, 15 are female (including all 11 infants). This is a considerably higher proportion than the 50% chance that nature offers.
Still, many remain unconvinced. Dr Robert Stillman of the American Society of Reproductive Medicine described the results as “a series of anecdotes” that have yet to be proved. The number of pregnancies was too small to be significant, and the technique necessarily reduces the viability of sperm so that an initial sperm sample of some 50 million motile sperm results in about 100000 to 300000 motile viable sperm for insemination.
Moreover, the exposure of these sperm to a DNA binding agent and to ultraviolet light raises obvious questions about safety and mutagenicity. The oncogenic potential of such exposure may not be realised for decades.
The researchers point out that many studies have shown that bisbenzimide is a non-toxic, reversible DNA binding stain and that analysis with polymerase chain reaction has shown no increase in DNA damage in sperm undergoing the Microsort procedure over controls. “Most important,” they say, “as in the animal data in several species with hundreds of normal births, all offspring born from flow cytometric separation of human sperm have been normal and healthy.”
In addition to safety concerns, moral considerations abound. Some worry that reproductive technology is ushering in an era of designer families and that if the desired sex is not produced, the customer may abort the fetus merely because of its sex. Some bioethicists, such as Arthur Caplan of the University of Pennsylvania, feel that the arrival of the Microsort technique of sex selection will accentuate sex biases.
However, Lawrence Gostin, a professor of law and public health at Georgetown University, told the CNN television channel that the procedure could be advantageous: “In this case, science is doing something that can have some manifest good. It can prevent disease and also … promote family and human happiness.”
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