Eyes on Evidence: Weight management during pregnancy

Feet on ScalePregnancy is thought to be an ideal time for health professionals to discuss weight management because women are motivated to make changes that will benefit themselves and their baby.   Across Europe and the USA, up to 40% of women gain more than the recommended weight in pregnancy (Thangaratinam and Jolly 2010). Excessive weight gain during pregnancy is associated with a number of serious health problems, including hypertension, gestational diabetes, and pre-eclampsia.
Current advice: There are no evidence-based UK guidelines on recommended weight-gain ranges during pregnancy. NICE recommends that weight loss programmes should not be used during pregnancy as they may harm the health of the unborn child. However, health professionals are advised to dispel any myths about what and how much to eat during pregnancy. For example, there is no need to ‘eat for 2’ or to drink full-fat milk. Energy needs do not change in the first 6 months of pregnancy and increase only slightly in the last 3 months (and then only by around 200 calories per day).
NICE advises that women stay active during pregnancy. Moderate-intensity physical activity will not harm a pregnant woman or her unborn child. At least 30 minutes of moderate intensity activity is recommended each day.
New evidence: A systematic review and meta-analysis evaluated the effects of diet, exercise, or a combination of the 2 on weight gain during pregnancy and any adverse effects on the mother or baby (Thangaratinam et al. 2012). 
The analysis included 44 randomised controlled trials involving 7278 women. The interventions were classified into three groups: those mainly based on diet (13 randomised trials), physical activity (18 randomised trials), or a mixed approach (13 randomised trials). 
Typical dietary interventions included maintenance of a food diary and a balanced diet consisting of carbohydrates, proteins, and fat. Typical physical activity interventions included, light intensity resistance training, weight bearing exercises, and walking for 30 minutes. The interventions in the mixed approach included counselling sessions, education concerning the potential benefit of diet and physical activity, and feedback on weight gain in pregnancy. The mixed approach used techniques of behavioural modification to give the women insight into controlling periods of emotional eating and preventing binge eating sessions.

Results showed weight management interventions in pregnancy to be effective in reducing maternal weight gain without any adverse risk on the baby. Dietary intervention reduced gestational weight gain by 3.84 kg on average (95% confidence interval CI -5.22 to -2.45), compared with 0.72 kg for exercise (95% CI -1.20 to -0.25) and 1.06 kg for a mixed approach (95% CI -1.67 to -0.46).

The diet based interventions effective in reducing weight gain in pregnancy included: a ‘balanced’ diet of 1.952.06 kcal/lb (1824kJ/kg); a low glycaemic diet with unprocessed whole grains, fruits, beans and vegetables; and a ‘healthy’ diet with a maximum of 30% fat, 1520% protein, and 5055% carbohydrate.
Diet also offered the most benefit in preventing pregnancy complications such as pre-eclampsia (33% reduced risk), gestational diabetes (61% reduced risk), gestational hypertension (70% reduced risk) and premature birth (32% reduced risk). The authors stressed that the overall evidence rating was low to very low for these outcomes.
The authors concluded that dietary and lifestyle interventions in pregnancy are safe and improve outcomes for both mother and baby, but acknowledged that data are needed on risk factors such as age, ethnicity and socioeconomic status.
Commentary: “This meta-analysis shows clearly that, across the whole pre-pregnancy body mass index (BMI) range, gestational weight gain can be reduced by dietary intervention. The reduction achieved is, however, very modest.
“It must also be appreciated that that there was no difference between control and intervention groups in those women who managed to achieve the BMI specific gestational weight gain limits recommended by the USA Institute of Medicine. These are the recommendations adopted by many countries but not, as yet, the UK. There remains inadequate evidence therefore to recommend modification of the current guidelines, which call for an evidence based intervention that will improve pregnancy outcomes.
“No single dietary regimen has yet been shown with adequate certainty to simultaneously reduce gestational weight gain and improve relevant clinical outcomes. Importantly, a subgroup analysis in obese women showed that a minor reduction in gestational weight gain occurred without any evidence of clinical benefit. Until such time as an intervention is shown with an adequate degree of certainty to limit gestational weight gain and reduce macrosomia, pre-eclampsia, gestational diabetes and other related outcomes, then there is inadequate reason to change clinical practice. In the meantime, the current NICE recommendations should contribute to limitation of excessive weight gain while preventing substantial NHS investment in potentially expensive interventions with limited evidence for success.” – Professor Lucilla Poston, Head of Division of Women’s Health, St Thomas’ Hospital, London.

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