Underweight during pregnancy

If your BMI shows that you are in the 'underweight' range, you might be advised to eat more than someone who is in the normal range during pregnancy

How can being underweight in pregnancy affect me and my baby?

If your BMI was less than 18.5 before you became pregnant, you may be advised to gain more weight than someone who is in the normal range.

Being underweight can bring a small increased risk of pregnancy problems such as premature birth (before 37 weeks) or having a baby that is underweight.

Your midwife may recommend a multivitamin supplement that's suitable for pregnancy, including folic acid, vitamin D and iron, and eating healthy extra calories to put on weight.

What will my midwife do if I am underweight?

If you have suffered, or are suffering, from an eating disorder, gaining weight might be hard for you to manage.

If this is the case, tell your doctor or midwife that putting on weight while pregnant may raise difficult feelings for you.

Midwives are trained to discuss this possibility, and should be able to put you in touch with extra support. Although it may be difficult, it's important to be honest.

Extra support, such as counselling from a mental health professional, can help you cope with the challenges around eating healthily during your pregnancy.

If depression or any other mental health condition is affecting your weight, and your ability to gain a healthy amount, your health care team may recommend safe medication for you to take.

Your midwife may refer you to the hospital antenatal clinic for extra scans to check on your baby's growth and development. You may also be referred to a dietician to help you work on ways to eat well and gain a healthy amount of weight.

Your midwife, or the specialist who is advising you, will discuss with you what your target weight gain in pregnancy should be. This will be based on a number of factors, including your pre-pregnancy weight.

They might also ask to weigh you regularly during your pregnancy to check on your progress.

What can I do for a healthy pregnancy weight gain?

When thinking about what to eat to gain weight, choose foods that are high in healthy fats, such as fish, chicken, nuts, avocados and unsaturated fats such as oils and spreads made from sunflower or olive oil.

Eat more pasta, beans and wholegrain cereals. Aim to eat three small meals and three healthy snacks every day.

Cakes, sweets and sugary drinks may put the weight on but have very little nutrition in them for you or your baby so try not to rely on these to gain weight.

Looking for more tips on what to eat in pregnancy? Find out more about having a balanced diet.

If you are exercising a lot or you have a very busy schedule, try to cut down your activity a bit. It's still important to be active in pregnancy, but you don't need to do more than the recommended amount of activity which is 30 minutes a day at least four days a week. 

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  1. Bhattacharya Sohinee, Cambell Doris, Liston William (2007) Effect of Body Mass index on pregnancy outcomes in nulliparous women delivering singleton babies. BMC Public Health 2007, 7:168
  2. Han Z, Mulla, S et al (2010) Maternal underweight and the risk of preterm birth and low birth weight: a systematic review and meta-analyses, International journal of Epidemiology
  3. Sebire NJ, Jolly M et al (2001) Is maternal underweight really a risk factor for adverse pregnancy outcome? A population-based study in London. BJOG. 2001 Jan;108(1):61-6.
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Last reviewed on February 1st, 2015. Next review date February 1st, 2018.

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