Maximum of two embryos best in IVF

By Sophie Ramsey

BMJ Group News

What do we know already?

Many couples turn to IVF if they’re trying for a baby and haven’t been helped by other fertility treatments. The man’s sperm is mixed with the woman’s eggs in a lab, so that the eggs become fertilised. Doctors then put one or more fertilised eggs (embryos) into the woman’s womb.

Although IVF has been used for decades, there’s ongoing debate about how many embryos should be implanted at one time. Using more than one embryo can increase a woman’s chances of having a baby. But it also increases the risk of a multiple pregnancy, which means a higher risk of premature birth and other problems. Some experts argue that a higher number of embryos is justified for women who are 40 and older, as a woman’s chances of becoming pregnant through IVF decrease as she ages. However, not enough good research has been done to know for certain.

In the new study, researchers gathered data on all IVF treatments done in the UK from 2003 through 2007, looking at how often women had babies after IVF, how often there were problems, and how these outcomes varied depending on how many embryos were used and the women’s ages.

What does the new study say?

For women of all ages, their chances of having a baby were higher if two embryos were used rather than one. However, using two embryos raised the risk of twins, premature births, and low birth-weight babies. These risks were higher for women under 40, suggesting that using a single embryo may be preferable for many younger women.

Most strikingly, the researchers found that using three embryos rather than two did not improve women’s chances of having a baby, and actually decreased the odds for women under 40. Using three embryos also carried a higher risk of problems, particularly very premature births (before the 33rd week of pregnancy).

These findings were based on 124,148 cycles of IVF, resulting in 33,514 live births.

How reliable is the research?

This was a large study that pulled information from a comprehensive database on all IVF treatments done in the UK. The researchers also took account of several factors that can affect IVF success, including the women’s ages, how long they’d been trying for a baby and the cause of their fertility problems (if known). All these things make the findings more reliable.

Even so, we can’t be entirely certain of these results as this wasn’t a randomised controlled trial (RCT), which is the best type of study for comparing treatments. However, a large RCT is unlikely to be done, as researchers would need to randomly assign thousands of women to have different numbers of embryos implanted. Previous RCTs have shown that women having IVF are often reluctant to participate in this type of study.

What does this mean for me?

Based on these findings, the researchers recommend that no more than two embryos be used in IVF regardless of a woman’s age, as this won’t improve her chances of having a baby and can increase the risk of problems. This is in line with current UK guidelines, which advise that a maximum of two embryos be used during each cycle of IVF.

If you’re under 40 and having IVF, these findings also suggest that having one embryo can minimise your risk of problems. You might discuss these findings with your doctor when deciding how many embryos are right for you.