I am fat and someone mentioned that I have a raised BMI. What is it and how can it negatively affect my pregnancy?

I’ve always been excited about the prospect of pregnancy as I, uninformedly so, thought pregnancy equals a free ticket to feasting away! Unfortunately, as medical practice is more and more based on research and good evidence arising internationally, I have to share with you the hard facts…

BMI or Body Mass Index refers to the calculation of your weight which is divided by your length times length: Wt/length². Internationally it is agreed that a normal BMI lies between 18.5 and 25. Between BMI of 25 and 29 one is overweight, and obesity is defined as a BMI above 29.

What does international data say about the risks for the obese patient during and after pregnancy:

  • The risk of developing diabetes in pregnancy (which results in a very high risk pregnancy) is at least doubled compared to the general population. Especially if you also have PCOS.
  • Increased risk to develop pre-eclampsia (serious type of blood pressure condition which only occurs in pregnancy). Risk at least doubled in the obese patient and more so if morbidly obese (BMI> 40).
  • The fetus is at increased risk of having a neural tube defect like spina bifida, or other developmental defects like cleft palate, limb defects and cardiac defects.
  • Increased risk to develop urinary tract infections which could precede development of preterm labour.
  • In terms of labour itself: Potentially longer duration of labour and higher risk of conversion to caesarean section.
  • If caesarean section: Increased risks for anaesthetic complications, excessive blood loss and development of infection in wound sites and blood clots (emboli) postpartum.

Management of the obese patient therefore starts pre-conceptually (when you are considering the thought!):

  • Dietician referral pre-pregnancy and establishing an exercise program (which should continue when you fall pregnant).
  • At least 5mg of folic acid supplementation daily starting @ 6 weeks prior to conception.
  • Stop smoking.

If pregnant already: (do not worry, we’ll help you through it!)

  • Your gynaecologist will probably screen you for diabetes at booking and again at 28 weeks pregnancy with a blood test.
  • You might be referred to a dietician while you are already pregnant! The obese patient will be advised not to pick up more than 5-9kg from pre-pregnancy weight, and the overweight patient, not more than 7-11.5kg. (guidelines from the IOM: Institute of Medicine)
  • The NT (12-13week)-scan and detail scan will be very important to rule out fetal abnormalities.
  • You might be referred to a specialist ultrasonography unit for your detail scan at increased levels of obesity since increased fat under the skin makes scanning more complicated.
  • If you should be induced for a specific reason later in your pregnancy, you might be admitted to an in-hospital high care facility for the duration of your induction.
Bottom line:

Let us be grateful at the fact that we are empowered with the knowledge to potentially dramatically influence our pregnancy outcome, for our unborn and ourselves…

You can use the following calculator to determine your BMI:

Internationally it is agreed that a normal BMI lies between 18.5 and 25. Between BMI of 25 and 29 one is overweight, and obesity is defined as a BMI above 29.

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