From nhs website
"Any woman can develop gestational diabetes during pregnancy, but you're at an increased risk if:
yourbody mass index (BMI)is above 30 – use thehealthy weight calculatorto work out your BMI
you previously had a baby who weighed 4.5kg (10lbs) or more at birth
you had gestational diabetes in a previous pregnancy
one of your parents or siblings has diabetes
your family origins are south Asian, Chinese, African-Caribbean or Middle Eastern
If any of these apply to you, you should be offeredscreening for gestational diabetesduring your pregnancy."