Scanning for the strongest embryo

Annika Levitt initially resisted the fertility clinic’s suggestion that only one embryo — rather than the usual two or more — be transferred to her uterus because she was too small to risk carrying more than one baby.

“You go through all that and you put only one back in?” she recalled thinking, fearing it would lower her chances of becoming pregnant. But her embryos had been tested for chromosomal abnormalities, giving a fair degree of confidence that the chosen one was healthy.

“Knowing that it was the strongest of the strong was reassuring,” she said. Ms Levitt, gave birth to a girl from that embryo and is now pregnant from another single-embryo transfer.

The chromosomal testing is one of the techniques now coming into use to help fertility clinics answer one of their most vexing questions: Which test-tube embryo or embryos will give a woman the best shot at having a baby?

Both techniques can potentially provide more information than the approach now used to judge an embryo’s fitness, which is to look at its shape under a microscope.

That could increase the sometimes frustratingly low efficiency of in vitro fertilization.

And if clinics can be nearly certain that an embryo is fit, they might feel more comfortable transferring only one embryo rather than two or more, as is common practice.

That would reduce the chances of producing twins or triplets, which face greater health risks than single babies.

New techniques

“What’s really good about this is we get high rates with singletons,” said Dr. Richard T Scott Jr, clinical and scientific director at Reproductive Medicine Associates of New Jersey, where Ms Levitt went.

But some experts say the new techniques, which can add thousands of dollars to the cost of in vitro fertilization, are being heavily promoted without data supporting that they truly improve pregnancy rates.

For some women, they say, chromosomal testing, an invasive procedure, might even worsen their chances of getting pregnant.

“A significant portion of women may actually be hurting themselves by doing that,” said Dr. Norbert Gleicher, medical director of the Centre for Human Reproduction, a fertility centre in Manhattan. The chromosomal testing is called preimplantation genetic screening, or PGS.

This is different from a related technique called preimplantation genetic diagnosis, which tests embryos for specific mutations with the goal of preventing the birth of a baby with a genetic disease.

With the chromosomal screening, the goal is mainly to improve birthrates, not influence the traits of the baby.

Ms Levitt, who is 33, initially sought in vitro fertilization to avoid having babies with a genetic disease for which she and her husband carry mutations. Despite some doubts, use of the new techniques seems to be expanding rapidly.

“We doubled the volume in 2013 over 2012,” said Dr Santiago Munné, director of Reprogenetics, a laboratory that does embryo screening for fertility clinics.

Other laboratories that do this include Genesis Genetics, Reproductive Genetics Institute and Natera. Dr Scott’s clinic developed its own test, which it also performs for other clinics.

Illumina, the largest manufacturer of DNA sequencing machines, is also making a push into the arena. It acquired BlueGnome, a British company that sells DNA chips used by some laboratories to do the testing.

Illumina also recently introduced a system that uses sequencing for embryo screening.

Even for younger couples, as many as half the embryos created in a test tube have chromosomal abnormalities, a major reason embryos fail to implant in the uterus or result in miscarriages.

So it seems logical that weeding out the defective embryos would increase the chances of a successful pregnancy. But that has proved illusory once already.

A study presented at the European Society of Human Reproduction and Embryology meeting on June 30 found that different testing techniques can yield different results for the same embryo, suggesting that not all the tests are accurate.

Also, some embryos die between Day 3 and Day 5 and lose the chance to be transferred. While those embryos might have been abnormal anyway, there is a chance that waiting five days to test could be costly, especially for older women, who produce fewer eggs.