A lucrative product in reproductive medicine is embryo screening, especially for women over 35. A single cell is removed from an embryo and checked for genetic defects which might make a successful pregnancy impossible. If the results are normal, the embryo is implanted into the womb. But does the technique, called pre-implantation genetic screening, lead to more pregnancies? Some experts say that fertility clinic promote it because the tests are so profitable — up to US$5,000 each time.

A study in the New England Journal of Medicine says No. It suggests that PGS actually lowers an older woman’s chance of becoming pregnant. Based on a study of 408 women aged 35 to 41, Dutch researchers found that women whose embryos were screened had a substantially lower pregnancy rate than those who did not: 25% versus 37%.

What could account for this? Dr Sebastiaan Mastenbroek, of the University of Amsterdam, is not sure. However, he says that removing a single cell might do more harm to the embryo than doctors have previously believed. Other experts were dismissive of the survey. “The way they performed this process tells us that they did not have a lot of expertise in this,” says Dr Anna Ferraretti, of the Italian Society for the Study of Reproductive Medicine.