Caesarean babies have an increased risk of becoming heavyweight adults, say researchers.
An analysis of data on 38,000 individuals found those born by Caesarean section were 22 per cent more likely to be obese than those who had natural births.
They had a 26 per cent greater chance of being overweight, as defined by their body mass index.
Scientists warned mothers to be aware of the possible long-term consequences of Caesareans.
Effects of a surgery-assisted birth on a baby’s gut bacteria and genes could be two reasons for the trend, they believe.
Professor Neena Modi, from Imperial College London, said: “There are good reasons why C-section may be the best option for many mothers and their babies, and C-sections can on occasion be life-saving. However, we need to understand the long-term outcomes in order to provide the best advice to women who are considering Caesarean delivery.
“This study shows that babies born by C-section are more likely to be overweight or obese later in life. We now need to determine whether this is the result of the C-section, or if other reasons explain the association.”
Caesareans now account for up to a third of births in England, twice as many as in 1990.
In some countries the C-section rate is much higher, with 60% of mothers in China and almost half in Brazil undergoing the procedure.
Previous research has linked other adverse outcomes in childhood including asthma and insulin-dependent Type 1 diabetes to Caesarean birth.
The new study pooled together results from 15 separate studies conducted in 10 countries.
This kind of “meta-analysis” can often uncover patterns that only emerge from large amounts of data.
The research showed that adults born by C-section have a BMI around half a unit higher on average than those born by vaginal delivery.