Written by:

Dr Diane Farrar

RM, BSc health science, BSc psychology, PhD reproductive endocrinology

Dr Diane Farrar is a practising midwife with over 25 years’ experience. She is a senior research fellow at the Bradford Institute for Health Research and visiting associate professor at the University of Leeds. Her research, which includes the areas of diabetes, high blood pressure, obesity and memory function, has been published in leading medical journals.

Pregnancy care for women who are overweight or obese

In this article:

  • How can a woman tell if she is overweight?
  • Should women who are overweight try to lose weight before they become pregnant?
  • Should women who are overweight try to lose weight once they find out they’re pregnant?
  • Overweight while pregnant: what are the risks?
  • Does being overweight during pregnancy pose any risks to the baby?
  • Are there extra tests or monitoring required for overweight women?
  • Weight loss following pregnancy
  • Main Points

Pregnancy care for women who are overweight or obese

Around half women of childbearing age are overweight or obese. Being overweight can affect a woman’s ability to become pregnant and carry her baby to term and can increase the risk of some pregnancy complications.

How can a woman tell if she is overweight?

Calculating body mass index is the most usual way of finding out whether a person’s weight is within the healthy range or whether they’re underweight or overweight. Body mass index (BMI) is a measure of weight and height, so there is a mathematical calculation: divide weight in kilograms (kg) by height in metres (m) and then divide the answer by height again to get BMI.

The World Health Organization has provided categories to describe different levels of weight for all people:

BMIClassification
less than 18.5:Underweight
18.5 – 24.9Normal weight
25 – 29.9Overweight
30 – 34.9Class I obese
35 – 39.9Class II obese
40 upwardsClass III obese

Should women who are overweight try to lose weight before they become pregnant?

Being in the best possible health before pregnancy gives the best chance of becoming pregnant and having a successful pregnancy and a healthy infant. So preparing for pregnancy by losing excess weight is recommended for overweight women.

Should women who are overweight try to lose weight once they find out they’re pregnant?

Currently there is no evidence to show that weight loss during pregnancy is beneficial or safe. Because of this, women are not advised to try and lose weight while they are pregnant. There is some evidence that during pregnancy women who are obese may not gain as much weight as normal-weight women, and some obese women may be more likely to lose weight. It is not clear why this happens, but it may be that adopting a healthier lifestyle during pregnancy influences weight change in obese women differently than for women who are at a healthy weight.

Although losing weight during pregnancy is not recommended, excessive weight gain can be harmful. The UK National Institute for Health and Care Excellence do not provide estimates of what constitutes ‘usual weight gain’ because the evidence around weight-gain ranges during pregnancy is limited. It is clear, however, that the amount of weight a woman gains in pregnancy can vary but should be gradual and correspond with the small weight increases of the growing baby and placenta and with minimal laying down of maternal fat. There is no need to increase calorie consumption so no need to ‘eat for two’ or to drink full-fat milk because energy needs change very little in the first six months of pregnancy and increase only slightly in the last three months (and then only by around 200 calories per day).

Overweight while pregnant: what are the risks?

Most overweight and obese women will not have any problems during pregnancy. However – although risk increases are relatively small compared to women in the healthy weight range – obese women are more likely to have a miscarriage or stillbirth, have either a shorter (preterm birth) or a longer pregnancy (so are more likely to have their labour induced and have problems around the time of birth that increase the chance of having a caesarean or forceps birth), and develop several pregnancy-related medical conditions.

Pregnancy is sometimes thought of as a ‘test’ for future health. Obesity outside of pregnancy increases the risk of several medical conditions including diabetes (high blood sugar levels) and heart disease, and similarly obese women are more at risk of developing gestational diabetes and high blood pressure in pregnancy. All women who develop gestational diabetes or high blood pressure irrespective of their weight are more likely to develop these medical conditions in later life.

Does being overweight during pregnancy pose any risks to the baby?

Compared to a baby born at term, a baby who is born early (before 37 weeks of pregnancy) is at a higher risk of being admitted to the neonatal unit, needing supplementary feeds, and developing various medical conditions including respiratory problems, such as asthma, and growth and developmental delays. Infants born to obese mothers are more likely to be heavier and to have greater levels of body fat compared to infants born to mothers with a BMI in the healthy range. Babies born heavier have a higher risk of obesity and diabetes in later life.

Are there extra tests or monitoring required for overweight women?

Women who are overweight may require extra care during their pregnancy, but this will depend on how overweight a woman is and if she develops a medical condition (such as gestational diabetes or preeclampsia) or complication (such as a larger than average infant). Women who are obese may be offered attendance at a specialist clinic where they can see health professionals (for example, an obstetrician, anaesthetist, midwife and dietician) who are knowledgeable of the risks linked to maternal obesity, what can be done to minimise these risks, and how best any complications should be managed.

Weight loss following pregnancy

Women should aim to start losing weight gained during pregnancy within six months of childbirth; when exactly a woman is ready will depend on her unique situation. All women should eat a healthy balanced diet, undertake a moderate amount of physical activity (20 to 30 minutes three to four times a week) and lose weight gradually (0.5-2lb per week). Weight loss goals should be realistic and weight loss programmes can provide support and encouragement and may increase the chance of success. It is also good to remember that breastfeeding can help weight loss and will benefit baby and that moderate-intensity physical activity and gradual weight loss will not affect a mother’s ability to breastfeed or the quantity or quality of breast milk.

Main Points

  • Around half of childbearing age women are overweight or obese. Being overweight can increase the risk of pregnancy complications.
  • Calculating body mass index (BMI) is the most usual way of finding out whether a person’s weight is within the healthy range.
  • There is currently no evidence to show that weight loss during pregnancy is beneficial or safe. Therefore, women are not advised to lose weight while pregnant.
  • The amount of weight a woman gains during pregnancy can vary, but it should be gradual and should correspond with the weight increases of the baby.
  • Energy requirements change very little in the first six months of pregnancy and increase only slightly in the last three months (and then only by around 200 calories per day), so there is no need to increase calorie consumption.
  • Women should aim to start losing weight gained during pregnancy within six months of childbirth, although the exact time to start losing weight will is individual and based on the woman’s situation.