Effects of interventions in pregnancy on maternal weight and obstetric outcomes: meta-analysis of randomised evidence

BMJ 2012; 344 doi: http://dx.doi.org/10.1136/bmj.e2088 (Published 17 May 2012)
Cite this as: BMJ 2012;344:e2088

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This review claims that diet intervention leads to a reduction in weight gain of 4 kg. However, the 2 largest studies constituting 73% of the included patients in the diet subgroup, only reduced weight gain by 1.7 and 2.2 kg. So how can the meta-analysis come to this result? In the case of extreme heterogeneity, as in this case (I^2=92%) care in the interpretation and analysis of the data needs to be taken. Using a random effects model will mean that the two studies with a 1000 patients will receive the same weight as the studies that include 20 patients. With 8 smaller studies the 2 large studies will relatively not get any weight. This inappropriate use of random effects model has led the authors to the exaggerated estimate. A fixed effect model would give a result of around 2 kg, but these studies might be too different to combine.

The two large studies also allowed insulin treatment primarily in the "diet arm" which raises concerns of whether the effects were caused by diet or insulin.

Competing interests: None declared

Jeppe Schroll, PhD Student

The Nordic Cochrane Centre, Tagensvej 22

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Metformin is known to be helpful in weight loss in adults1. A multicentral trial viz. MiG (Metformin in Gestational Diabetes) has shown encouraging results when compared to women of GDM on insulin.

Children exposed to metformin had larger measures of subcutaneous fat, but overall body fat was the same as in children whose mothers were treated with insulin alone2. According to the authors- Janet A. Rowan, Elaine C. Rush, Victor Obolonkin et al in their study entitled-" Metformin in Gestational Diabetes: The Offspring Follow-Up (MiG TOFU) Body composition at 2 years of age" published in Diabetes Care (October 2011 vol. 34 no. 10 2279-2284)2:

1. The Metformin in Gestational diabetes (MiG) trial prospectively compared pregnancy outcomes in women with gestational diabetes mellitus (GDM) randomized to either metformin (plus supplemental insulin as required) or insulin treatment.

2. The primary outcome, a composite of neonatal complications, was not significantly different between the treatment arms. Secondary outcomes, including body anthropometry at birth, were also not different between the treatment arms.

3. Metformin does cross the placenta in significant amounts, although neonatal outcomes are same as on insulin, but it is important to examine longer term outcomes such as fat composition in childhood.

4. Further follow-up is required to examine whether these findings persist into later life and whether children exposed to metformin will develop less visceral fat and be more insulin sensitive. If so, this would have significant implications for the current pandemic of diabetes.

1. http://www.drmirkin.com/nutrition/N117.htm
2.doi: 10.2337/dc11-0660
Diabetes Care October 2011 vol. 34 no. 10 2279-2284

Competing interests: None declared

Neeru Gupta, Scientist E

Neeta Kumar, KK Jani

Indian Council of Medical Research, Ansari Nagar, New Delhi-110029

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We refer to the comprehensive systematic review and meta-analysis of randomized controlled interventions to reduce gestational weight gain (GWG) in pregnancy by Thangaratinam et al [1]. The mean reduction in GWG across all studies was relatively small at 1.42kg (0.95-1.89kg). Clearly, reducing GWG in pregnant women is challenging, even though small differences do contribute to a better outcome.

Anecdotally, women diagnosed with gestational diabetes (GDM) gain less weight than those without GDM after this diagnosis is made, presumably secondary to changes in their diet and activity levels. However, there is little formal documentation of this in the literature.

We prospectively recorded GWG in 108 women from diagnosis of GDM at 26-28 weeks, to 36 weeks gestation, compared with 339 women without GDM. In this brief 9 week period, GDM women gained a mean of 2.1 ± 2.51kg compared to 5.16 ± 2.42 kg in women without GDM (p<0.001), resulting in less total GWG (12.2 ± 5.17 kg versus 15.0 ± 5.03 kg, p<0.001) (figure 1). GWG prior to the diagnosis of GDM was similar in both groups using self-reported prepregnancy weight.

GDM women had a greater mean estimated prepregnancy body mass index (BMI) of 24.5 ± 4.9kg/m2 versus 22.8 ± 3.9 kg/m2 (p<0.001) and were more likely to be non Caucasian (57.4% versus 26.5%, p<0.001). Third trimester weight gain remained significantly decreased in GDM women after accounting for BMI category and ethnicity. GWG was not associated with blood glucose levels at either the fasting or 2 hour time point on the 75g diagnostic glucose tolerance test, suggesting that even women with mild GDM are capable of losing weight with interventions for GDM. As we used fasting and 2 hour cut-offs of 5.5mmol/L and 8.0mmol/L respectively, some of these women would no longer fit the criteria for GDM based on the recent IADPSG diagnostic criteria.

The primary management goal in GDM is achieving target blood glucose levels on home blood glucose monitoring, not weight reduction. Women at our centre were reviewed once by a diabetes educator (with an additional visit if they required insulin) for education on the importance of blood glucose control, home blood glucose monitoring and dietary advice, advocating regular and well-spaced low glycemic index carbohydrates and a low fat diet. They were advised to undertake 30 minutes of exercise per day such as walking. They were not routinely assessed by a dietician nor by an exercise physiologist. They were reviewed every 1-3 weeks by the diabetes clinic medical team that instituted pharmacotherapy if their blood glucose levels were above target range.

Perhaps a key difference between women with GDM and those who participate in weight loss interventional programs with the sole aim of reducing weight gain is the availability of daily performance feedback indicators such as home blood glucose monitoring, as well as a strong motivation to reduce the perinatal complications of GDM and to avoid insulin treatment. Yet most interventional trials to reduce GWG focus on adherence to a diet or exercise program as a primary goal, rather than the psychology or goal setting strategies behind creating behavioural change in pregnant women [2].

Further research should aim to evaluate the key psychological motivators and performance feedback indicators that facilitate lifestyle and dietary behavioral change in pregnancy for the benefit of mother and baby.

1. Thangaratinam, S., et al., Interventions to reduce or prevent obesity in pregnant women: a systematic review. Health technology assessment, 2012. 16(31): p. iii-iv, 1-191.
2. Brown, M.J., et al., A systematic review investigating healthy lifestyle interventions incorporating goal setting strategies for preventing excess gestational weight gain. PloS one, 2012. 7(7): p. e39503.

Competing interests: None declared

Sue M Lau, Endocrinologist

Suja Padmanabhan, Amy Wagstaff, Valerie Tung.

Royal Hospital for Women, Barker St Randwick Sydney NSW Australia 2031

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Thank you very much for this excellent article. As a comment and working hypothesis in our research team, we wrote recently a letter in the American Journal of Clinical Nutrition (Gestational weight gain: arguments for a transgenerational weight-control process. AJCN 2012, PMID: 2226802) since we observed in a French cohort of pregnant women a negative correlation between BMI before pregnancy and gestational weight gain. This occurred without any intervention during pregnancy in the two maternity wards involved in that research. In an older article we also observed that 3% of pregnant women lost weight during pregnancy (Decreased full breastfeeding, altered practices, perceptions, and infant weight change of prepregnant obese women: a need for extra support. Pediatrics 2008, PMID: 18450874).

The mean weight loss you report seems reasonable. However, to date any intervention during pregnancy must be cautious avoiding too restrictive or unbalanced regimens. The effect on fetal growth should be monitored. Spontaneous weight gain regulation may occur and is currently under investigation.

Competing interests: None declared

Régis HANKARD, Pr of Pediatrics

Inserm CIC 0802, CHU Poitiers, Poitiers, France

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How have you calculated the mean values for all interevntions combined because I cannot work out how if you average 3.84, 0.72 and 1.06 you get 1.42kg instead of 1.87kg the averagaes for the sample that exclude diabeteics also dont add up to the expoected average

Competing interests: None declared

Kallum Rhule, Student Dietitian

n/a, 18 Woodpecker Close, London, N9 7nd

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Question What information is available on exercise as a lifestyle intervention, during and after pregnancy to assist with weight loss? Summary answer NICE guidelines (CG62) for antenatal care recommend BMI is calculated at booking (10 weeks). 38% of women surveyed thought they needed to lose weight. However, half of these were unaware of their BMI. This highlights a need for better education of pregnant women about ideal body weight and the need for better access to and clearer guidelines about activities which are safe during the ante-natal and post-natal periods

Competing interests: None declared

Sangeeta Agnihotri, consultant obstetrician & gynaecologist

Cheryl Wang, James Duffy

Whipps Cross Hospital, London E11 1NR

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Why is the statistic that half the women who die during pregnancy, or childbirth are either obese or overweight significant? - given that half the population are similarly either obese or overweight. I don't doubt the many problems caused by obesity in pregnancy but, unless I'm missing something, I don't think this particular statistic is supportive evidence

Competing interests: None declared

Kate J McCambridge, Midwife

RSCH, Brighton

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