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Assessing levels of maternal malnutrition

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Victoria Sibson

independent nutritionist

Normal user

18 Sep 2010, 10:29

In Niger the 2006 MICS estimated 19.2% of women of reproductive age to be malnourished (with a BMI<18.5) and 1.9% severely malnourished (BMI<16). In Zinder the rate was 29.6% and in Diffa 31.2%. Aside from making a judgement call (1/3 women malnourished in Zinder and Diffa sounds enormous), or looking at trends in these rates over time, the seasonal timing, likely causes etc (as per the 'best practice' process for interpreting malnutrition rates in children), does anyone have any advice on how to objectively assess the severity of the nutrition situation among women based on these rates?

Mark Myatt

Consultant Epideomiologist

Frequent user

18 Sep 2010, 16:55

In brief ...

You (or whoever did the MICS) have been collecting the wrong data.

At length ...

There is a major problem with using BMI for estimating the prevalence of undernutrition. Both acute and chronic undernutrition present as low BMI but the process leading to a low BMI may be acute or chronic and the examination of a single BMI value does not allow these two very different conditions to be differentiated from each other. You can think of this as being a bit like using W/A in young children. Low W/A can be "wasting" or "stunting" but, given a single low W/A figure alone, we cannot tell what is happening. Apart from this very major problem, there are problems with using BMI relating to diurnal variability in height, diurnal variability in weight, error and variation in height associated with acute undernutrition, difficulties in measuring height, the effect of oedema and ascites on weight, and age-related changes in body size / shape / composition but the BIG PROBLEM is body shape.

Body shape is frequently determined by the sitting height to standing height ratio (SSR):

SSR = Sitting Height / Standing Height

This index varies considerably both between and within populations. International comparisons have found average SSR to vary between 0.48 (in Australian aborigines) and 0.55 (in Japan). This range translates into differences in BMI due to body shape alone of over 6 BMI units. In one Australian aborigine population the SSR was found to vary between 0.41 and 0.53. This is larger than the worldwide variation in average SSR and translates into differences in BMI in excess of 10 BMI units due to body shape alone. What this means is that people with long-limbs and short-trunks (common in populations living in hot climates with milk in their diets) tend to appear undernourished (by BMI) due to body shape alone. BMI can be adjusted using a correction factor based on SSR but you need to measure sitting height to do that.

Oh ... I almost forgot ... BMI is useless for pregnant women. See the thread:

http://www.en-net.org.uk/question/215.aspx

I'd guess that body-shape is a factor in the high prevalences you report. I've been to Zinder and (if I remember right) it was hot and the population was agro-pastoralist / pastoralist.

Without the corection for SSR and the censoring of pregrant women there is no way to "objectively assess the severity of the nutrition situation among women based on these rates".

So ... if BMI is problematic, what can we use instead? Well ...

Mid upper arm circumference (MUAC) is the circumference of the left upper arm measured at the mid-point between the tip of the shoulder and the tip of the elbow. MUAC is useful for assessing the nutritional status of children. It is better at predicting mortality in children than any other anthropometric index. The MUAC measurement requires little equipment and its use can be easily taught to minimally trained workers.

Until recently the use of MUAC was restricted to children aged between 12 and 59 months. The lower age-limit has recently been reduced to six months and work is ongoing to evaluate the use of MUAC in both younger and older children. MUAC has been used to assess the nutritional status of adults during famine and its use for this purpose was recommended by United Nations Forum for Nutrition in July 2000.

The strong associations between MUAC and body weight and MUAC and nutrient reserves in muscle and fat in adults are well established. MUAC is not affected by oedema or pregnancy and is independent of height.

The use of MUAC has not been fully evaluated as a prognostic indicator in adults but estimates of arm muscle area (AMA) and corrected (i.e. for humerus cross section) arm muscle area (CAMA) form parts of well validated diagnostic procedures for adult undernutrition in hospital settings and are used as prognostic indicators in elderly and cancer patients. The use of AMA and CAMA require accurate measurements of skin-fold thickness and are impractical for use in primary healthcare settings or field-based surveys in developing countries. MUAC is a more practicable measure and is strongly correlated with both AMA and CAMA.

MUAC thresholds for diagnosing acute undernutrition in adults, derived by extrapolation from well-nourished populations in developing countries without reference to data collected during famines, have been proposed:

http://www.ncbi.nlm.nih.gov/pubmed/8785188

These thresholds have been shown to be associated with increased mortality and morbidity in chronically undernourished populations. Data from famines suggests that thresholds extrapolated from well-nourished populations may not be useful for assessing acute undernutrition in adults and alternative thresholds for this application have been proposed:

Normal >= 185 mm
MAM < 185 mm
SAM < 160 mm

These thresholds were developed for use in famines where resources (i.e. for adult therapeutic feeding) are likely to be scarce and primary undernutrition is common. Primary undernutrition develops when nutrient intake in insufficient to provide for normal physiological needs and, in adults, this is invariably due to lack of food. Secondary undernutrition develops when an underlying disease process (e.g. HIV/AIDS, TB, or cancer) increases metabolic demand and / or decreases food intake or utilisation. Neither BMI or MUAC can differentiate between primary and secondary undernutrition. It is important to note that primary and secondary undernutrition are the result of different underlying pathophysiological processes and the functional significance of anthropometric indicators is also likely to differ.

Different thresholds to those give above have been used in programs providing nutritional support to pregnant and lactating women, people living with AIDS, and the chronically sick and are suitable for diagnosing acute undernutrition in non-emergency or chronic care situations:

Normal >= 210 mm
MAM < 210 mm
SAM < 185 mm

It should be noted that there is, at present, little data on the relationship between MUAC and mortality and other functional measures in adults. Thresholds based on mortality risk cannot be presented with the same degree of certainty as is possible with children. The first set of thresholds presented above have, however, been used in several settings and have been found to be more strongly predictive of mortality than BMI. The second set of thresholds have been shown to be associated with increased mortality and morbidity in chronically undernourished populations.

Sorry not to be of more help.

Tamsin Walters

en-net moderator

Forum moderator

4 Oct 2010, 13:26

From Victoria Sibson:

Dear Mark

Thanks a lot for your response. This is helpful. I wonder if and when these big national level surveys (MICS, DHS) will start measuring MUAC so we can address some of the challenges you outline.? In the meantime I will propose to our teams to consider measuring maternal MUAC in our SMART surveys and see what response I get

Thanks

Vicky

Mark Myatt

Consultant Epideomiologist

Frequent user

4 Oct 2010, 14:15

Happy to help.

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