Babies who are born by caesarean are 50% more likely to be obese before the age of five, research has found.
They are also more likely to suffer asthma during childhood, while their mothers face greater threat of future miscarriage and infertility.
A review on the long-term risks of caesarean sections, which looked at 79 large scientific studies, found that an average of 9.2 in every 100 babies born naturally were obese before the age of five.
But that rises to almost 14 out of every 100 babies for those who were born by caesarean.
This 51% increased risk could be because babies surgically removed from the womb are not exposed to important bacteria as they would be if they had passed through the birth canal.
Without it, their metabolism and their body’s ability to store fat may be affected.
Dr Sarah Stock, who was co-author of the review from the MRC Centre for Reproductive Health at the University of Edinburgh, said: "Although we cannot conclude that caesarean delivery causes certain outcomes, pregnant women and clinicians should be aware that caesarean delivery is associated with long-term risks for the baby and for subsequent pregnancies."
"The significance that women attribute to individual risks and benefits is likely to vary, but it is imperative that clinicians take care to ensure that women are made aware of any risk that they are likely to attach significance to."
In Britain, more than a quarter of babies are delivered by caesarean section every year. The rate rose from 24.1% to 27.1% in the decade to 2015-16, with some blaming the increase on the rise of women who are ‘too posh to push’, opting for the operation when there is no medical reason for it. The review found the biggest impact on children from caesarean births was their weight.
Asked why, Dr Stock said: "We did not look at causes, but cannot exclude that recovery from caesarean section may affect breastfeeding rates, with breastfed children less likely to be obese.’
Babies born by caesarean were nearly 20% more likely to have asthma before the age of 12. Asthma rates rose from around 3.05 in 100 babies born naturally to 3.65 in every 100 who had C-section births.
This may also be due to missing out on bacteria in the birth canal, which can protect against the allergies which cause wheezing and breathlessness.
The review shows women who have had caesareans are about a third less likely than those who have had a natural birth to fall pregnant again.
This infertility may be caused by an injury or infection in the womb after doctors cut into it to remove the baby safely. Scarring of the womb could also explain a higher rate of miscarriage among women who have had a caesarean.
And scarring could explain the 40% increased likelihood of ‘placental abruption’ – a condition where the placenta starts to come away from the womb wall before the baby is born, which can starve it of vital nutrients and stop the child growing properly.
However, the study, which was published in the journal PLOS Medicine, also concludes that women who have a caesarean are less likely to suffer urinary incontinence or a pelvic prolapse.