Keys (1972) provides an excellent review of indices of relative weight and obesity. His conclusions are that BMI is a good practical proxy for percentage body fat but that it could only be used in population studies and was not suitable for individual diagnosis. His work remains sound but BMI has been used widely for individual diagnosis and has been found to be lacking. There are many reasons for this. It is now not considered good practice to use uncorrected BMI in this way and BMI is gradually being replaced by alternative measures. Current thinking is that BMI is probably acceptable for diagnosing overweight or obesity in sedentary adults and for detecting within-population trends. BMI is weight divided by height squared. Weight changes quite a lot in pregnancy. We can make some guesses about pregnancy associated weight changes in the final few months of pregnancy: Baby 3.5kg Placenta 0.5kg Uterus 1.0kg Anmniotic fluid 2.0kg Breasts 0.5kg Blood 1.0 kg Fat 2.5kg Fluid in tissues 2.5kg All that comes to about 13.5 kg. You'll probably be able to find more accurate figures in the literature and do the numbers yourself but I do not think I am way off with these figures. Anyone got any better estimates? Let's consider a healthy women with a weight of 65 kg and a height of 1.65 m at conception. BMI at conception is 23.9. Add the 13.5 kg and we get a BMI of 28.7. Nothing much has changed in the nutritional status of the woman (i.e. all is as we would expect it to be) but the BMI has moved from "normal" to "overweight". An obvious point here is that pregnancy does odd things to BMI. The less obvious point is that we expect considerable weight gain associated with pregnancy. This means an "elevated" BMI. This means that BMI is unlikely to be a sensitive indicator of declining nutritional status during pregnancy (i.e. you look for a "low" value you really should be looking for a "normal" or "elevated" value). One way round this is to fiddle with the BMI thresholds but the normal range is so wide as to be able to hide many cases of declining nutritional status (i.e. you have a sensitivity problem) and the fiddle-factor would need to change depending on the stage of the pregnancy. You would probably want to have BMI (or just weight) at conception with a good guess at the date of conception and work from there ... but ... I think you interested in a single-shot measure for use in cross-sectional surveys or occasional screening. There are additional problems that apply to pregnant and non pregnant women: (1) BMI (like all W/H measures) is strongly affected by body shape (e.g. Somalis will tend to have very low BMIs just because they tend to long legs and short trunks). This can be fixed by using different cut-offs in different populations (e.g. in Singapore the normal range has been defined as 18.5 - 22.9 since about five years ago) or by correcting for the Cormic Index (sitting to standing height ratio) which is not easy to do as it requires an additional measurement and a more complicated formula. (2) Height is known to change significantly during the day due to the compression effect of gravity with height being greatest in the morning. This means that BMI values are dependent on the time of day in which height is measured with BMI being lowest in the morning. The effect of diurnal change in height are magnified by the squaring of the height term. (3) Weight may vary throughout the day depending on factors such as hydration and the contents of the gastro-intestinal tract. Such variability is likely to be a larger problem in children than in adults. (4) Acute undernutrition is associated with gross weakness, flexor contractions, and scoliosis which prevent the patient from standing straight. These present difficulties in measuring height which will tend towards underestimation of standing height which leads to overestimation of BMI. (5) Data from adults in famine situations and in labour camps providing minimal "starvation" rations demonstrate that height is lost during starvation. This loss of height reduces the sensitivity of BMI in detecting acute undernutrition. (6) Data on the prevalence of nutrition-associated oedema from emergency, concentration camp, and experimental settings indicate that oedema is a common complication of acute undernutrition in adults. (7) In adults, nutritional-associated oedema frequently presents as bilateral pitting oedema, facial oedema, and ascites. Ascites is not included in standard case-definitions of oedematous undernutrition in children and is uncommon in children. Ascites is, however, a common complication of acute undernutrition in adults and results in far greater spurious weight increases than bilateral pitting oedema. Retained fluid can frequently account for over 10% of body weight. Nutrition-associated oedema is associated with poor prognosis in both children and adults. This means that patients with oedema often have a poorer prognosis with higher values of BMI. BMI is not, therefore, an appropriate indicator for people suffering from nutrition-associated oedema. The problem is further complicated by the fact that the presence of facial oedema (sometimes called "moon-face") can give the impression that a patient is well-nourished. These problems make BMI difficult to recommend for your application Now to the punchline ... 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 and body-shape. The main issue is what threshold to use. 210 mm is common although I have seen this as high as 235 mm. I have, above, listed some problems with BMI. Here are the problems with MUAC: (1) 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. There is evidence, however, that MUAC is more strongly predictive of mortality than BMI. The 210 mm threshold has been shown to be associated with increased mortality and morbidity in chronically undernourished populations. (2) The use of MUAC in adults may be affected by the redistribution of subcutaneous fat from peripheral to central areas of the body during ageing. Age-specific MUAC thresholds may, therefore, be required for use in the elderly. This is not relevant in your application. (3) Abnormalities in the distribution of fat are a recognised complication of anti-retroviral therapy. ART-associated abnormalities in the distribution of fat may present as localised fat accumulations and / or localised fat losses. ART-associated fat loss differs from the generalised wasting seen in advanced HIV-infection because lean mass tends to be preserved. The problems introduced by ART-associated abnormalities in fat distribution are similar to the problem of age-independence (see above) although current research suggests that ART-associated fat loss is associated with small and non-significant decreases in MUAC. This is probbaly not relevant in your application. (4) Ethnic differences in MUAC have not been sufficiently studied to determine whether a single set of MUAC thresholds could be used in all ethnic groups. The evidence from children suggests that a single set of thresholds could be used in all ethnic groups. (5) It is often asserted that, in terms of precision and accuracy of measurement, MUAC compares unfavourably with weight-for-height based indices such as BMI. Evidence supporting such assertions is, however, elusive. Research with children demonstrates consistently better intra-observer and inter-observer reliability for MUAC compared to weight- for-height based indices. I hope this helps.

Dear Mark, it is not a reply but just a simple question, in one of our projects we have been providing High energy biscuits to the pregnant women (refugee). It is in Bangladesh. Now we have to meausre the effectiveness of the Biscuit (in a very simple way). How do we proceed, will MUAC be more useful for the Pregnant women than BMI as outcome? Ofcourse there would be some other indirect/ direct evidences. But I am more interested in MUAC/ BMI issue.........it confuses me a lot. Thank you.

What data did you collect at baseline? As Mark explained, MUAC is a better indicator of malnutrition during pregnancy due to specific body weight changes over pregnancy period. Low MUAC during pregnancy is also a strong predictor of Low Birth Weight which is one of the main indicators. I am also working in Bangladesh at the moment with a supplementary feeding product for malnourished pregnant women. We are in the piloting stages and having difficulties adapting out product for acceptability and quality (eg texture, taste). At the moment we have been forming a paste which the women eat but I have also been exploring the idea of using a biscuit. What ingredients and their quantities did you use to produce your biscuits? Do you have product design documents you could send through? My email is mon.kindy@gmail.com if needed. Cheers

Hi Kindy, thanks a lot for the response, I shall send you the specification as soon as I get back to Dhaka.

A key rationale for providing nutritional support during pregnancy is to reduce the incidence of low birthweight (and associated developmental and survival issues). So ... you could look at birthweight or chest-circumference in newborns. If you missed this or it is too difficult to collect then you could measure infant weight and look for low W/A. If the program was effective you should see very low prevalence of low birthweight / low chest circumference in newborns. If you go for W/A you should see very low prevalence of low W/A (i.e. very few children with W/A < -2 z-scores). You may also want to look at peri-natal and neonatal mortality. If you want to look at mothers then you would hope to see very low prevalence of MUAC < 210 mm. Is this any help?

From Asish Das: Dear Mark, thanks a lot for your very clear and to the point answer. In fact we will now be doing both 1) Birth weight of the infant 2) MUAC of the pregnant women after every 4 weeks starting from 3 months pg till she deliver. This would consist of two groups 1) Mothers who are on Nutrition supplementation and 2) Mothers who are not suffering from Malnutrition and hence not on Nutritional supplementation. Eventually we would compare these two groups. Thanks a lot, -Asish

That sounds good. (1) You would be testing that birth weight of children of the treated mothers (i.e. treated because they have low MUAC) is similar to the birth weight of the children of untreated mothers (i.e. not malnourished). You may also want to measure chest circumference (this is a simple measurement). Your analysis could be of proportions LBW in each group of of means in each group. (2) Is a more complicated analysis as you have repeated measures. You might want to simplify this with the MUAC of the mother taken when you measure weight at birth. This could also be an analyse of proportions or means.

Hi Asish Have you arrived back in Dhaka yet? I would love to know your formula for the feeding product you have designed. I am heading back to the field today and need to have everything clarified by the end of the week. Cheers

Actually can anyone help me out with this!! I am currently designing a locally made supplementary food for pregnant women in Bangladesh. I am using lentil powder, ground peanuts, milk powder, salt sugar and oil and would like to form a paste. My problem is that when following the WHO guidelines I can not get enough moisture (oil) in there without going way above the % of fat. I do not want to advise the mixing with water due to clean water not always being available. Has anyone done anything similar? If so can you tell me your ingredients and the proportions to form a paste. If not, I will need to trial with biscuits. Cheers

Dear Anon 1445, I have moved your question to the Prevention and treatment of moderate acute malnutrition forum area, as it doesn't relate to assessment, and you may find people to assist you there. Please continue this discussion on that thread: [url]http://www.en-net.org.uk/question/858.aspx[/url]. Best wishes Tamsin