Weighing scales for young infants: a survey of relief workers

By Chloe Angood

Chloe has a background in Development Studies, and previously spent thee years working with an NGO in Zimbabwe. For the past year she has been working part-time with ENN on projects related to infant feeding in emergencies. This research was carried out for her MSc in Public Health Nutrition dissertation with the University of Southampton, UK.

Infants under 6 months are particularly vulnerable in emergencies, usually as a result of inappropriate feeding practices¹. Interventions to prevent and treat infant malnutrition in emergencies depend on an accurate assessment of infant nutritional status and a prerequisite to weighing is an effective set of weighing scales. However, there is a lack of guidelines and information about which weighing scales to use for infants. In the WHO field guide, hanging spring scales measuring in 100g graduations are recommended for weighing infants from birth². However, this does not consider the need for weighing scales with greater precision for the management of severely malnourished infants. In the recent Multicentre Growth Reference Study (MGRS) portable electronic scales with taring ability³ were used (specifically the UNICEF electronic scale 890 or UNISCALE)⁴. However, these scales have not been tested in emergencies, or with very low weight infants.

A baby being weighed on a home visit in South Africa

Repeated communication to the Emergency Nutrition Network (ENN) suggest that the lack of clear guidelines in this area is a frustrating hindrance to emergency programming, and can prevent the anthropometric assessment of young infants in emergencies altogether⁵. The University of Southampton conducted the following study with help from the ENN in order to provide a first step to bridging this lack of guidance.

Project Design

The objective of this study was to discover the type of weighing scales most commonly used by humanitarian relief workers to weigh infants under 6 months in emergencies and the type of weighing scales that this group believes to be most suitable for this purpose in order to generate a hypothesis for field trials. The results of field trials would then form the basis of recommendations to humanitarian relief workers.

Between June and August 2006, a cross-sectional survey was carried out by email and telephone. The subjects were 41 humanitarian relief workers from different UN agencies, international and local non-governmental organisations (NGOs) and governments, working in 25 different countries. All subjects worked in emergency nutrition programmes and had recent direct experience weighing infants under 6 months.

Results

Types of scales currently used in the field

Table 1 displays the different types of scales used by respondents, (illustrated in Figures 1). Table 1 shows that by far the most commonly used type of weighing scales are hanging spring scales. The second most popular are balance beam bowl. Only three respondents used adult bench scales (UNISCALE) and no respondents used infant bench scales.

All hanging scales used by respondents are made by Salter and, in 23 out of 26 cases, this is the Salter 235 6S model. Most balance beam scales used are made by Seca and in 6 out of 8 cases this is the Seca 725 model.

Data reveal some interesting differences when analysed by the different contexts in which respondents work. Figure 2 displays the types of weighing scales used in exclusively clinical settings (such as therapeutic feeding centres), exclusively community settings (for example in community surveys) and those used in both. This demonstrates that respondents tend to use different scales for different purposes (this difference is statistically significant, p=.035). Specifically, respondents are more likely to use balance beam scales in exclusively clinical contexts and hanging scales in the community.

Opinions about the suitability of weighing scales used

Respondents were asked their opinion on the suitability of the scales that they use for weighing infants under 6 months. Respondents believe that different types of scales have different strengths and weaknesses. These are summarized in Table 2. Overall, respondents believe balance beam scales to be the most suitable type of scales to weigh infants under 6 months in emergency situations and hanging scales to be the least suitable.

An ideal set of weighing scales

Respondents were asked questions about the features of an ideal set of weighing scales for weighing infants under 6 months in emergencies. A high proportion of respondents stated that mechanical scales are most suitable and, second to this, solar powered scales. This suggests that mains and battery power are difficult to sustain in emergency situations. Respondents generally agree that scales should be light and precise, with a fairly low maximum capacity, measuring in small graduations. Most respondents do not believe that a secondary function is necessary, however, the most popular secondary function of those mentioned is to measure infant length.

Key points

Humanitarian workers believe all existing types of weighing scales to be limited in some way in weighing infants under 6 months in emergency situations. No ideal set of weighing scales exists.

Hanging spring scales, specifically the Salter 235 6S model, are the most common type of scales used by respondents for weighing infants under 6 months in emergencies.

Respondents tend to use different scales for different purposes; in clinical settings they are likely to use more precise scales, usually balance beam scales, and in community settings (and where respondents use the same set of weighing scales in both) they tend to use less precise scales, usually hanging spring scales.

Humanitarian workers rate hanging scales as the least suitable type for weighing infants under 6 months in emergencies, even though they are the type used most frequently.

Respondents regard balance beam scales as the most suitable type of weighing scales out of those that exist. Balance beam scales are rated higher than others in terms of precision, function and ease of use and fairly highly on portability and durability.

Adult bench scales and infant bench scales are relatively unused by humanitarian workers and are therefore untested by the study.

Conclusions

Different weighing scales are needed for weighing infants under 6 months in emergencies. Demands may be satisfied by balance beam scales, however their suitability needs to be tested in field trials. Adult bench scales and infant bench scales also need to be tested. Manufacturers could consider developing a new type of weighing scales specifically designed for weighing infants under 6 months in emergencies.

Design Brief for an ideal set of weighing scales

On the basis of this study, the criteria for an ideal set of weighing scales for weighing infants under 6 months in emergencies are as follows:

Precise: able to measure in very small graduations (20g)

Functional: Able to hold and measure very small infants. Infants should be held securely with their heads supported, with maximum comfort and minimum handling. An adult bench scale with taring capacity could be considered for this purpose (where infants are held in their mother's arms during weighing). Ahelpful additional function would be to measure infant length. The scales should also accommodate a wider age group than just infants under 6 months (at least all children under 5 years).

Easy to use: As easy as possible to use, to enable the scales to be used by personnel who are not highly skilled, and to avoid measurement errors. Must be easy to calibrate (if possible self calibration), put together/ set up, place infant/child on the scales and read the result (possibly digital display). Pictorial instructions could also be etched onto the scales so that they cannot be lost.

Highly portable: Able to carry scales easily and comfortably by hand. They must therefore be lightweight and pack down to a shape that is easy to carry, with a handle. Any attachments also need to be highly portable within this.

Adapted to field conditions: Able to operate in extreme hot and cold temperatures and either mechanical or powered by a renewable energy source (e.g. solar or wind up power). Must not have holes that will allow dirt/ sand to get in. It should be possible to use the scales on a non-flat surface. Hanging is not preferable, unless selfhanging.

Durable: Must be highly durable due to frequent transportation, rough conditions and heavy use.

Low cost: Must be low cost (it must either last a long period of time, or be very easy to replace) to make it affordable. The most commonly used scales at present (hanging spring scales) cost £60-£100 and are replaced every 2-4 years with heavy use.

The full research report is available on the ENN website, http://www.ennonline.net/docs.html

Call for Collaboration

The Institute of Human Nutrition at the University of Southampton is now actively seeking to develop the technology to fulfill the above criteria and plan to test prototype equipment against existing types of scales in field trials. The University of Southampton is seeking to work with interested organisations in the development of this product and in field trials. The ENN will continue to communicate with the University of Southampton on this. If you would like to be involved, or to find out more, please contact Chloe Angood, email: chloe@ennonline.net

¹WHO-UNICEF (2003) Consultation on child health in complex emergencies, 21-22nd October, 2003. Geneva: WHO.

²WHO (2002) The management of nutrition in major emergencies. Geneva: WHO.

³Allows the scales to be set to zero while someone is standing on it.

⁴De Onis, M., Onyango, A.W., Ven den Broeck, J., Chumlea, W,C. and Martorell, R. (2004) Measurement and standardization protocols for anthropometry used in the construction of a new international growth reference. Food and Nutrition Bulletin, 25 (1), supplement 1.

⁵Prudhon C. (2000). Including infants in nutrition surveys. Field Exchange Issue 9, p15.