IVF babies tend to be lighter than others but end up heavier

Since the first “test tube” baby arrived 39 years ago, an estimated 6.5 million children have been born thanks to IVF and similar techniques. But we are only just starting to learn about the long-term health of people conceived using assisted reproduction techniques (ART), who may have a higher risk of obesity in later life.

“Today, 1 in every 30 babies in Japan is conceived by ART,” says Tomoya Hasegawa of Tokyo Medical University. IVF babies are usually healthy, but tend to have a lower birth weight. Large studies that didn’t look at conception method have previously found that low birth weight is linked to adult obesity and diabetes.

To investigate further, Heleen Zandstra of Maastricht Medical Centre, the Netherlands, and her team have been comparing the effects of using two different culture media to support the growth of early IVF embryos. Earlier they had found that one of these was associated with babies that were 112 grams lighter at birth than those beginning life in the other medium. “That’s a big difference, considering babies only weigh about 3 kilograms,” says Zandstra.

Now the team have followed up on these babies at the age of 9, recording the height, weight and fat mass of 136 children, as well as their blood pressure and heart rate.

They were surprised to find that, while children conceived using each type of culture medium were around the same height, the BMI of the group that had been lighter at birth was an average of 0.9 lower than those who had been heavier babies. “There was a difference in weight of 2 kilograms,” says Zandstra.

Gene activity

However, both groups were heavier than average 9-year-olds living in similar circumstances, and had more abdominal fat. Given that heavier children are more likely to become obese later in life, the results are worrying, says Zandstra, who presented her findings at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) in Switzerland in July.

At the same meeting, Hasegawa presented his analysis of 1830 children in Japan. His team found that babies conceived using ART were heavier than naturally conceived babies when they were born, but there was no real difference at 18 months. However, the ART children were heavier again at 6 years old. “The results were surprising,” says Hasegawa.

These findings add to growing evidence that there’s something about ART that seems to affect the way embryos develop. Previous studies have found that children conceived using ART in Norway seem to have a slightly higher risk of developing blood cancers later on, while other research has linked ART to a higher risk of birth defects.

One theory is that fertility treatments may affect a person’s future health by altering the activity of genes in developing embryos. The first few days of development are vital for determining which genes will be switched on or off for the rest of an individual’s life, and the process of culturing embryos before implanting them has been found to affect this in mice.

Unknown effects

Research in human embryos has found that differences in culture medium can affect the health of embryos, and specifically favour the development of male or female embryos, but it’s difficult to pinpoint what might be causing this because the ingredients of ART culture media are a closely guarded industry secret.

But it’s also possible that the health differences seen in people conceived through ART may not be caused by the techniques used, but instead be related to their parents’ infertility.

What the findings in babies and children will mean for adult health is not yet unknown. Louise Brown, the first person born via IVF, is only 39 – we don’t know yet what will happen to IVF-conceived people in their 50s, says Zandstra.

But people needn’t be wary of fertility treatment. “We know that IVF is safe, because we have so many children,” says Arianna D’Angelo, who coordinates the ESHRE group on safety in assisted reproduction. “We shouldn’t worry, but we should be doing more to monitor children. Studies might flag up problems later in life,” says D’Angelo.

Source: New Scientist