Is weight loss safe during pregnancy?

Weight Loss During Pregnancy: Safety and Recommendations

Weight loss during pregnancy is generally not recommended due to potential risks to maternal and fetal health, except in specific medical circumstances such as co-existing diabetes or hypertension where it may be considered under close medical supervision. 1

Current Guidelines on Weight Management During Pregnancy

General Recommendations

• Multiple clinical practice guidelines (CPGs) indicate there is insufficient evidence to recommend weight loss during pregnancy 1, 2
• Instead, the focus should be on appropriate weight gain based on pre-pregnancy BMI 1
• 13 CPGs recommend that pregnant women with obesity be informed about the importance of controlling weight gain during pregnancy, not losing weight 1

Weight Management Strategies During Pregnancy

• Use of BMI at first prenatal visit to guide diet and exercise counseling according to Institute of Medicine (IOM) recommendations 1
• Moderate physical activity is recommended:
  • 150 minutes per week 1
  • 30 minutes per day of moderate intensity exercise 1
  • Beginning with low-intensity exercise and gradually increasing 1

Medical Considerations for Weight Loss in Pregnancy

Weight loss during pregnancy may only be considered in specific circumstances:

• One CPG noted that weight loss during pregnancy should be based on medical considerations such as co-existing diabetes or hypertension 1
• However, two other CPGs explicitly stated there is no evidence to recommend weight loss during pregnancy 1

Risks Associated with Weight Loss During Pregnancy

The Cochrane review found no randomized controlled trials designed to reduce weight in obese pregnant women, highlighting the lack of safety data 2. Observational studies show mixed results:

• Some suggest improved outcomes for conditions like pre-eclampsia
• Others indicate increased risk of small-for-gestational-age infants 2

Pre-Pregnancy Weight Management

Rather than focusing on weight loss during pregnancy, guidelines strongly emphasize:

1. Pre-conception weight loss: 13 CPGs recommend stabilizing weight before conception or achieving inter-pregnancy weight loss 1

   • Obesity is associated with increased risks of neural tube defects, preterm delivery, diabetes, cesarean section, hypertensive and thromboembolic disease 1
   • Weight loss before pregnancy reduces these risks 1, 3

2. Nutritional supplementation:

   • Women with BMI ≥30 planning pregnancy should take 5 mg of folic acid daily, starting at least 1 month before conception and continuing through first trimester 1
   • Vitamin D supplementation for those with deficiency 1

Practical Approach to Weight Management During Pregnancy

For women who are already pregnant:

1. Calculate BMI from pre-pregnancy weight and height
2. Provide gestational weight gain counseling based on pre-pregnancy BMI
3. Focus on healthy nutrition and appropriate physical activity
4. Consider referral to a dietitian, especially for women with obesity 1
5. Monitor for pregnancy complications associated with obesity (gestational diabetes, pre-eclampsia)

Common Pitfalls to Avoid

• Intentional weight loss attempts: Despite guidelines, approximately 7.5% of pregnant women report trying to lose weight 4
• Inadequate nutritional intake: Even when controlling weight gain, adequate nutrition remains essential
• Excessive exercise: While moderate exercise is beneficial, excessive or high-intensity exercise may pose risks
• Delayed care: Women with obesity should have early booking visits to plan appropriate care 1

For women planning pregnancy who have obesity, the focus should be on achieving weight loss before conception rather than during pregnancy, as pre-pregnancy weight loss has been shown to improve pregnancy outcomes and reduce complications 3.