Public Release: 

Sorting the girls from the boys

European Society of Human Reproduction and Embryology

Lausanne, Switzerland: A team of American scientists and physicians has developed a pre-conception sex-sorting technique for humans that can dramatically increase the percentage of female embryos obtained through IVF from a half to more than 90%.

It means that couples undergoing pre-implantation genetic diagnosis (PGD) for disorders linked to the X chromosome can have a 9 out of 10 chance that the embryo biopsied will be female. This will significantly increase the number of female embryos available for transfer to the woman's uterus. Having a girl is very important to couples who have x-linked disease because a boy would have a 50% chance of being affected by life-threatening single gene diseases such as muscular dystrophy or haemophilia.

Team member Dr Harvey Stern, giving the latest results from an ongoing clinical trial to the European Society of Human Reproduction and Embryology annual meeting in Lausanne today, (Wednesday 4 July) said that the technique, which uses a flow cytometer known as MicroSort , was the first 'sex sorter' of its type in the world to be used for humans.

"We have already used MicroSort in 14 PGD cycles for six different X-linked genetic disorders resulting in 112 embryos for biopsy. We have additional data from 28 PGD cycles, with 172 embryos for biopsy, from couples undergoing IFV because they wanted a girl to balance their families," he told the conference.

"We were able to be unambiguous in assigning gender in 90% of the 284 embryos. Of these, 92% were female and 8% were male. When we have done PGD cycles without MicroSort we have seen more or less equal numbers of male and female embryos - as predicted by FISH data, which show that most men have approximately equal proportions of X and Y- bearing sperm."

Dr Stern said: "MicroSort is currently still undergoing clinical trial, but we already know that it substantially increases the chance of a couple having a child of a particular gender. It reproducibly increased the proportion of X-bearing sperm and resulted in a dramatic rise in the percentage of female embryos obtained after IVF - up from 50% to over 90%.

"Another important factor is that it may result in sufficient embryos for one or more frozen embryo transfer cycles as well, which means the woman may be able to avoid having to undergo additional IVF cycles if the first transfer is unsuccessful."

He said that as of May this year, 297 MicroSort pregnancies had been achieved and 187 babies had been born so far. The MicroSort facility is currently based at Fairfax but other locations are being considered and semen can be sorted and frozen for use with IVF and/or PGD by collaborators around the world.


Abstract no: O-208


A number of important inherited disorders involve genes located on the X chromosome. Most are recessive, which means that females, who have two X chromosomes (XX), need both copies of the affected allele to show clinical signs of the disorder, though they may be 'silent' carriers. However, males have only a single X chromosome (XY) and can show the disorder if they carry just one copy of the affected allele.

Microsort technology is based on the fact that the X chromosome is substantially larger than the Y chromosome. Since chromosomes are made of DNA, human sperm cells having an X chromosome will contain about 2.8% more total DNA than sperm cells with a Y chromosome.

This DNA difference can be measured and the X and Y-bearing sperm cells individually separated using a modified flow cytometer instrument. The resulting purity (enrichment) of the separated sperm cells can be determined by a DNA analysis method (FISH). The flow cytometric sperm separation technology was originally developed in animals by Dr Lawrence Johnson at the US Department of Agriculture and has been further developed by the Genetics and IVF Institute for use in humans.

FISH is a technique that uses DNA probes that specifically attach to either the X or Y chromosome in sperm and emit a red/pink colour for X-bearing sperm and green for Y-bearing sperm. The X and Y-bearing sperm can be identified and counted under a microscope

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