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The number of babies born by Caesarean section has affected human evolution, a study has suggested.

The study suggests C-sections allow women with narrow pelvises to give birth when they or their babies' lives might previously have been at risk - and this means the genes for narrow pelvises are passed on to future generations, leading to further Caesarean deliveries.

But there are many other factors involved in whether or not a woman will have a C-section.

Some are commonly believed to determine if a woman will give birth naturally or via by Caesarean - but the evidence used by the NHS says they don't...

An X-ray of the pelvis won't be able to predict if you can give birth naturally

If you are short and have small feet, that doesn't mean your body is too petite for a natural birth

Likewise, carrying a big baby doesn't mean you will definitely need a Caesarean

If you have had a previous section, it doesn't necessarily mean you can't try for a natural birth next time

Things that won't make a difference...

walking around while in labour

not lying on your back during labour

having an epidural

getting into water during labour

having labour induced or having your waters broken

But a planned Caesarean might be necessary if...

you are expecting twins

your baby is in the breach (bottom-down) position

your baby is premature

you have a low-lying placenta

you have HIV, hepatitis or herpes

And sometimes an unplanned Caesarean delivery might be required when...

there is concern about your health or your baby's health

your labour is not progressing

you have vaginal bleeding during pregnancy or labour

you go into labour before the date of your planned Caesarean section

But if you are pregnant and have any concerns or questions, it's always best to speak to your doctor or midwife.