Differences in growth, weight and body fat levels of children conceived through fertility treatment even out by the time they hit their late teens, a study has suggested.

Researchers say their findings indicate that the differences between children born through methods like IVF and those conceived naturally are small and unlikely to have any health implications.

The study was aimed at addressing concerns around whether fertility treatment is associated with growth, weight and body fat from infancy to early adulthood.

Since the first IVF baby was born, there have been questions about the risks facing children conceived this way.

Previous studies have shown an increased risk of low birthweight and pre-term birth in babies conceived by assisted reproductive technology (ART), but relatively little is known about long-term growth and weight gain.

The research found that people conceived using ART were on average shorter, lighter and thinner from infancy up to early adolescence compared with their naturally conceived peers.

However, the differences were small across all ages and reduced with older age.

Dr Ahmed Elhakeem, senior research associate in epidemiology at the University of Bristol, and lead study author, said: “This is important work.

“Over the last three decades conception by ART has increased.

“In the UK just over one in 30 children have been conceived by ART, so we would expect on average one child in each primary school class to have been conceived this way.

“Parents and their children conceived by ART can be reassured that this might mean they are a little bit smaller and lighter from infancy to adolescence, but these differences are unlikely to have any health implications.

“We acknowledge it is important that as more people conceived by ART become adults, we continue to explore any potential health risks at older age.”

An international research group from the Assisted Reproductive Technology and Future Health (ART-Health) Cohort Collaboration, looked at whether conception by ART – which mostly involves IVF – was associated with growth, weight and body fat from infancy to early adulthood.

ART options include intrauterine insemination (IUI), in-vitro fertilisation (IVF), IVF with intracytoplasmic sperm injection (ICSI), and the use of donor sperm (donor insemination) or eggs (egg donation).

Using data on 158,000 European, Asian-Pacific and Canadian children conceived by ART, the data sample included 8,600 children from Bristol’s Children of the 90s study.

Peter Thompson, chief executive of the Human Fertilisation and Embryology Authority (HFEA), said: “Around one in seven couples have difficulty conceiving in the UK which leads to around 53,000 patients a year having fertility treatment (IVF or donor insemination).

“The findings from this study will come as a welcome relief to these patients who begin treatment in the hope of one day having healthy children of their own.

“Health outcomes in children conceived using assisted reproductive technology is a high priority for the HFEA and we monitor the latest research and provide information for patients and professionals.

“Anyone considering fertility treatment can access this and other high-quality impartial information on fertility treatments and UK licensed clinics at www.hfea.gov.uk.”

The findings are published in Jama Network Open.