Printed on: September 28th, 2025

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Obesity and weight management in pregnancy

Obesity and weight management in pregnancy

NICE published its guideline on nutrition and weight management in pregnancy in January 2025. Here, we summarise the key elements for us in primary care (NICE 2025, NG247).

This article was updated in August 2025.

• Both excess weight gain and low weight gain during pregnancy carry risks for the mother and baby.
• BMI assessment at booking is essential for risk stratification and appropriate care planning.
• Healthy eating and physical activity are key components of weight management, but should be approached with sensitivity.

• BMI ≥30 at booking: offer screening for gestational diabetes.
• BMI ≥40 at booking: consider referral to specialist obesity services.
• Do not routinely weigh patients unless clinically indicated (see below).
• Intentional weight loss is not advised during pregnancy due to potential adverse effects on the baby.

Managing weight in pregnancy is a key concern in primary care, given its impact on both maternal and foetal outcomes. This article provides an overview of best practices in obesity and weight management during pregnancy, as outlined by NICE (NICE 2025, NG247).

• Why weight matters in pregnancy.
• How to discuss weight with patients.
• Managing excessive and low weight gain, including when to screen for gestational diabetes.
• Healthy eating and physical activity recommendations.
• Referral pathways for specialist support.

Weight management in pregnancy plays a crucial role in minimising complications (NICE 2025, NG247). Both excessive and inadequate weight gain in pregnancy is linked to adverse outcomes. Excess weight gain increases the risk of gestational diabetes, hypertensive disorders and large-for-gestational-age (LGA) babies, while low weight gain is associated with small-for-gestational-age (SGA) babies.

Women entering pregnancy with a BMI in the overweight or obesity categories are at higher risk of complications, including caesarean section and postpartum haemorrhage.  Pregnant women with obesity also have an increased risk of venous thromboembolism, pre-eclampsia, miscarriage, wound infections and higher rates of mortality (BJOG 2019; 126:e62). Addressing weight proactively during the conception phase can mitigate some of these risks.

Many women may feel uncomfortable discussing their weight so it is essential to create a supportive and non-judgemental environment. The first antenatal appointment provides a key opportunity to assess BMI and discuss weight-related risks in a way that empowers rather than discourages patients.

• Measure BMI at the first antenatal appointment.
• Use sensitive language to avoid stigma and encourage engagement.
• Explain why BMI matters in a way that is patient centred.
• Offer written or non-verbal feedback on BMI if patients prefer not to discuss it verbally.

NICE emphasises that weight loss during pregnancy is not recommended due to potential adverse effects on the baby. However, addressing weight proactively during the preconception phase can mitigate some of these risks. We are encouraged to highlight the significant health benefits of weight loss before pregnancy (NICE 2025, 246).

In June 2025, the MHRA released guidance for women using GLP-1 agonists and planning pregnancy (MHRA alert June 2025):

• GLP-1 medications should be avoided during pregnancy due to lack of safety data.
• The MHRA recommends a ‘washout period’ after stopping these medications before trying to conceive:
  • Semaglutide: stop at least 2m before pregnancy.
  • Tirzepatide: stop at least 1m before pregnancy.
  • Liraglutide: no washout period is required.

Why? The MHRA highlighted some animal studies which identified harmful effects on the developing foetus. Further evidence is needed from human trials so watch this space!

RCOG guidelines on the care of women with obesity in pregnancy advise checking weight and BMI as part of routine preconception care, and supporting women to optimise their weight between or before pregnancies; this is associated with a reduced risk of stillbirth and hypertensive complications, and an improved likelihood of successful vaginal birth after caesarean section (GTG 72, 2019 BJOG 2019; 126:e62). Women with a BMI ≥30 should be given advice on the risks of obesity during pregnancy and childbirth.

The RCOG also advises waiting at least 12–18m after bariatric surgery before attempting pregnancy to allow both stablisation of body weight and the identification and treatment of any nutritional deficiencies that may not be evident in the early months (BJOG 2019; 126:e62).

Weight changes in pregnancy are expected. However, there are some indications for more regular monitoring of weight, and some cases where more detailed assessment might be required (NICE 2025, NG247).

A non-exhaustive list suggested by NICE includes…

• Gestational diabetes.
• Hyperemesis gravidarum.
• Thromboprophylaxis.

There is no clear definition or consensus around what constitutes excessive weight gain in pregnancy. However, if it is suspected, NICE says that we should:

• Assess physical and psychological factors contributing to weight gain.
• Encourage a balanced diet and appropriate physical activity.
• Monitor foetal growth to assess risk of LGA.
• Consider gestational diabetes testing (see below).

• Explore reasons such as nausea, vomiting, mental health issues or underlying medical conditions.
• Encourage nutrient-dense foods and ensure adequate calorie intake.
• Monitor foetal growth and consider additional support if concerns arise.

For women asking for more information on expected weight change in pregnancy, NICE recommends that we signpost to the National Academy of Medicine’s 2020 paper on expected gestational weight gain based on pre-pregnancy BMI (Table 1, The Current Understanding of Gestational Weight Gain Among Women with Obesity and the Need for Future Research - NAM).

Maintaining a healthy diet and staying active during pregnancy can contribute to better outcomes for both mother and baby. Nutritional guidance should be practical and culturally sensitive, ensuring that women feel supported in making changes.

(RCOG Health eating and vitamin supplements in pregnancy 2022, NICE 2025, NG247)

• Balanced, varied diet: encourage pregnant women to eat a wide range of foods – including plenty of fruits, vegetables, whole grains, lean proteins and dairy – to ensure both mother and baby get essential nutrients.
• Limit high-fat and high-sugar foods: advise reducing foods with high fat or sugar content to help manage weight and lower the risk of gestational diabetes.
• Folic acid supplementation: stress the importance of starting folic acid supplements before conception and continuing during early pregnancy to reduce the risk of neural tube defects.
  • Should we prescribe higher-dose folic acid? Older RCOG Green-top guidance on the care of women with obesity in pregnancy recommended that women with a BMI ≥30 take folic acid 5mg from one month before conception and for the first trimester ((BJOG 2019; 126:e62).
  • NICE concluded that there is no evidence to support high-dose folic acid for those with a BMI within the overweight or obese range, and the standard dose of 400mcg is sufficient unless other risk factors for neural tube defect or congenital malformation are present.
  • Those who have had bariatric surgery may require specialised advice on folic acid and other micronutrients before and during pregnancy. It is recommended to consult the patient’s bariatric surgery unit for guidance.

• Vitamin D supplementation: recommend vitamin D supplements, especially for those at risk of deficiency, to support bone health and immune function. There is insufficient evidence to recommend a specific dose of vitamin D, but current UK guidelines advise 10mcg (400 IU) daily during pregnancy and breastfeeding (NICE 2025 NG247).
• There is no one best diet for gestational diabetes: there is no convincing evidence that one diet is superior to another when it comes to managing gestational diabetes.

(NICE 2025, NG247)

• Encourage at least 150 minutes of moderate-intensity activity per week.
• Encourage minimising sedentary time, and suggest walking, swimming or prenatal yoga.
• Tailor advice based on pre-pregnancy activity levels and preferences.
• The Active Pregnancy Foundation has a wide range of resources for both patients and healthcare professionals.

The guidance highlighted that although nutrition and physical activity did not show significant efficacy in managing weight during pregnancy in randomised control trials, they were associated with reduced rates of gestational diabetes, pre-eclampsia and LGA.

Pregnant women with a higher BMI are at increased risk of developing gestational diabetes, which can lead to complications if left unmanaged (NICE 2025, NG247). Early screening and lifestyle interventions can help improve outcomes.

• Offer testing to patients with a BMI ≥30 at booking.
• Offer testing to those with additional risk factors (outlined in our Diabetes in pregnancy (including gestational diabetes) article).
• If excessive weight gain is observed, even if the BMI at booking is below 30, consider testing for gestational diabetes.
• Provide individualised dietary and lifestyle advice for those diagnosed.

For some women, specialist input is required to manage weight-related risks in pregnancy. Timely referrals can help ensure appropriate support.

• BMI ≥40 at booking: consider referral to a specialist obesity service.
• Refer to dietitians, midwives or physiotherapists for tailored support.
• Encourage access to peer support groups and digital resources.

Breastfeeding has particular benefits for women living with obesity and their babies:

• Reduced risk of maternal type 2 diabetes later in life. A meta-analysis of observational studies showed that any breastfeeding reduced the risk of T2DM by 27%, with an even greater benefit seen in women with a history of gestational diabetes (Diab Obes Metab 2021;23:1902).
• Reduced risk of obesity in adolescence and adulthood for the breastfed child (Lancet 2016;387:475 and Lancet 2016;387:491).

In June 2025, the MHRA released a reminder that GLP-1 medications should be avoided during breastfeeding. For more detail on safe use of medications related to obesity during breastfeeding, see Specialist Pharmacy Service: UK Drugs in Lactation Advisory Service – safety in breastfeeding.

Obesity and weight management in pregnancy Weight discussions should be non-judgemental and supportive. Encourage a balanced diet and safe physical activity rather than focusing on weight alone. Monitor but do not over-medicalise weight gain during pregnancy. Use BMI to guide screening and referrals appropriately. Support women to optimise pregnancy outcomes with practical and evidence-based resources. BMI ≥30: offer screening for gestational diabetes. BMI ≥40: consider referral to specialist obesity services. Do not routinely weigh patients unless clinically indicated.

Useful resources: Websites (all resources are hyperlinked for ease of use in Red Whale Knowledge) Active Pregnancy Foundation British Dietetic Association – pregnancy and diet National Academy of Medicine - the current understanding of gestational weight gain among women with obesity and the need for future research