The surprising new factor that decides whether your child will be obese or not relates to how you give birth…

Pregnant? According to JAMA Pediatrics, a study involving 22 068 children (4 921 born by Cesarean delivery) from 15 271 mothers were followed in the years following their birth. And, gasp, children born via Cesarean had a 15 percent increase in likelihood of being obese compared to those born by vaginal delivery.

In women delivering children by different methods, those born by Cesarean were 64 percent more likely to be obese than their siblings born vaginally.

The consistency of these findings suggests that this association may not be owing to other factors, but may actually represent a true biological effect…

READ MORE: You Can Go 9 Months Without Knowing You’re Pregnant

But why?

Researchers suggest the reason for elevated obesity risk could be that Cesarean delivered children do not have the same exposure to their mother’s vaginal and gastrointestinal microbiota.

Babies delivered vaginally have greater exposure to their mother’s vaginal and gastrointestinal microbiota compared with those born by Cesarean delivery, who are exposed mainly to their mother’s skin microbiota and external environmental bacterial communities at birth.

This early-life difference leads to an altered gut microbiota pattern in children. Compared with kiddies born vaginally, those born by C-section harbour more staphylococci, fewer bifidobacteria and less diverse bacteria species in microbiota colonisation, a pattern that has been linked with the risk of being overweight or obese in later life.

Will studies into this phenomenon are ongoing, it might be worth thinking hard about your chosen method of delivery, particularly if you’ve opted for a Cesarean section that is not medically-driven.

Looking for more on pregnancy? Here are 6 things you should know if you’re planning on exercising while you’re pregnant.