A STEROID may prevent repeated miscarriages, says a researcher who has shown the chemical can reduce the number of 鈥渒iller cells鈥� accused of causing miscarriages. But other experts say clinical trials to explore this would be too risky, not least because no one knows for sure what the cells do.
The controversy revolves around a type of immune cell with an evocative name: natural killer cells. Although the function of NK cells remains uncertain, there is some evidence that they assist the implantation of embryos in the womb. However, a few small studies suggest that high numbers of NK cells increase the risk of miscarriage.
Some private clinics already offer treatments such as steroids and immunosuppressants to reduce the number of NK cells in women who have suffered recurrent miscarriages. But claims of dramatic results, and the publicity given to them, have been attacked by fertility experts who argue that there is no scientific basis to the treatments. 鈥淭he link between the number of NK cells and their function is hard to make because we don鈥檛 know what they do,鈥� says Ashley Moffett of the University of Cambridge.
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Confusingly, there are two types of NK cells: peripheral NK cells in the blood, and uterine NK cells in the lining of the womb. Some clinics estimate the number of uterine NK cells based on the number of peripheral NK cells. But Moffett says that is like using the number of black cars in a city centre to estimate the number of red ones out on the motorway.
The latest study addresses this criticism. Siobhan Quenby of the University of Liverpool, UK, took samples from the wombs of 110 women who were not pregnant but had suffered an average of six miscarriages each. In 33 of these women, uterine NK cells accounted for at least 5 per cent of the cells in the sample, while in the other women they accounted for less than 5 per cent.
鈥淐laims of dramatic results have been attacked by fertility experts who argue there is no scientific basis to the treatments鈥�
Quenby asked the 33 women to take the steroid prednisolone, which is used to treat conditions such as asthma and eczema. NK cells have steroid receptors on their surface, and some studies suggest that steroids such as prednisolone knock out the receptors.
Twenty-nine of the women took 20 milligrams of prednisolone daily for 21 days from the start of their menstrual cycle. By day 21, uterine NK cell numbers had dropped by an average of 6 per cent compared with women not taking the steroid, Quenby told the European Society for Human Reproduction and Embryology meeting in Copenhagen, Denmark, this week.
The trial was originally going to stop at this point, but all the women demanded to be allowed to continue on the drug when they were told the results. 鈥淭hey were desperate for it,鈥� says Quenby. Six of the women have since become pregnant, with one pregnancy ending in miscarriage and two in births. The remaining three pregnancies are now beyond the point at which most miscarriages occur.
Quenby stresses that the results are preliminary and do not prove that an excess of uterine NK cells cause miscarriages. 鈥淲e urgently need clinical trials,鈥� she says.
But Moffett is not so sure. 鈥淪teroids have serious side effects and there may be additional risks to women in early pregnancy,鈥� she says. 鈥淲e鈥檙e not yet ready for clinical trials because we don鈥檛 know enough about what NK cells do. It鈥檚 too premature to say 鈥楻ight, let鈥檚 give everyone prednisolone鈥�.鈥�
