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Brief Reports

Indian Pediatrics 2002; 39:838-842  

 Mid Arm Circumference at Birth: A Screening Method for Detection of Low Birth Weight

 

S.L. Sood, G.S. Saiprasad and C.G. Wilson

 

From the Department of Pediatrics and Department of Preventive and Social Medicine, Armed Forces Medical College, Pune 411 040, Maharastra, India.

Correspondence to: Col. G.S. Saiprasad, Epidemiologist/Professor and Head, Department of Preventive and Social Medicine, Armed Forces Medical College, Pune 411 040, Maharastra, India.

E-mail: [email protected]

Manuscript received: July 8, 2001, Initial review completed: August 30, 2001;

Revision accepted: March 6, 2002.

 

The present study is an attempt at evaluating the utility of mid-arm circumference(MAC) to detect low birth weight in the neonatal period. This cross sectional study was conducted in 1272 newborns. The mid arm circumference ranged from 8.2 cm to 9.7 cm (mean 9.2 cm, 95% CI 9.15 cm, 9.19 cm). A positive correlation existed between MAC and birth weight (r = 0.76, 95% CI:0.73, 0.78; P<0.001). A mid-arm circumference of 8.7 cm predicts a birth weight of 2580 gm (95% PI 2071g, 3099g) and it definitely excludes newborns with birth weight <2000 g. Measurement of MAC is simple and valid method of screening for low birth weight babies.

Keywords: Low birth weight, Mid-arm circumference, Neonate, Screening test

Birth weight is one of the most sensitives and reliable predictors of the health of any community(1). Detection of low birth weight immediately at birth is of paramount

importance to ensure infant’s survival(2). Recording of accurate birth weight by primary health care workers has been a problem in rural areas leading to a search for an alternate, inexpensive, age independent and non invasive method to predict neonatal well being(3,4).

Many studies were carried out to evaluate the mid-arm circumference (MAC) as an indicator of low birth weight (LBW) and different values of MAC were advocated by various authors(5-7), but most of these studies did not provide a critical evaluation of MAC as a screening test. The present study attempts a detailed scrutiny of the concept of using MAC as a screening test.

Subjects and Methods

The present study was conducted at Command Hospital (Southern Command), Pune, a tertiary care hospital affiliated to the Armed Forces Medical College, Pune. Weight and MAC of 1272 newborns were recorded between 24 and 48 hours of life using standard techniques. Birth weight was the gold standard against which MAC was evaluated as surrogate in this screening marker evaluation study to detect low birth weight (LBW), i.e., < 2500g.

Sensitivity, specificity, positive and negative predictive values for various values of MAC were calculated and a receiver operating characteristic (ROC) curve was constructed to arrive at the optimum MAC cut off level(8). A simple linear regression model was fitted to predict birth weight from MAC values and 95% Prediction Intervals (95% PI) constructed to examine the range of error in prediction on account of sampling variation(9).

Results

Table I shows the distribution of birth weight and MAC by estimated gestational age (EGA). The MAC ranged from 8.2 cm to 9.7 cm with a mean of 9.2 cm (95% CI 9.15 cm, 9.19 cm). Statistically highly significant positive linear correlations were observed between MAC and birth weight (r = 0.76, 95% CI 0.73, 0.78; P<0.001), between EGA & MAC (r = 0.93, 95% CI 0.92, 0.93; P<0.001), and between EGA & birth weight (r = 0.67, 95% CI 0.62, 0.68; P<0.001).

Table II shows distribution of the study subjects by different MAC values and also by birth weight categorized as low birth weight (<2500g) or normal weight (2500g+). Sensitivity, specificity and positive and negative predictive values at these MAC values are shown. As cut off value of MAC is raised the sensitivity to detect low birth weight is seen to increase and the specificity is seen to decrease. It can also be seen from Table II that as the MAC value increases, the positive predictive value decreases and the negative predictive value increases. The ROC curve was plotted to identify the optimal cut off point of MAC (Fig. 1). The value of MAC as indicated by the ROC curve is 8.7 cm, and is considered as the optimal cut off point in this study.

Table I-Correlation of Birth Weight, Mid-arm Circumference and Estimated Gestational
 Age (EGA) in Newborns
Expected
gestational
age (weeks)
Infants
Studied
Birth weight (g)
Mid-arm Circumference (cm)
 
n
 %
Mean (SD)
95% CI
Mean (SD)
95% CI
37
147
11.2
2230(327)
2177,2283
8.5(0.14)
8.49, 8.54
38
208
16.4
2273 (266)
2703,2773
8.8(0.10)
8.79, 8.82
39
251
19.7
2971 (272)
2938,3004
9.0(0.14)
8.99, 9.03
40
548
43.4
3135(282)
3111,3159
9.4(0.14)
9.38,9.41
41
71
5.6
3109(266)
3046,3172
9.6(0.13)
9.57,9.63
42
47
3.7
3324(368)
3214,3430
9.8(0.11)
9.79,9.85
Total
1272
100.0
2950(400)
2928,2972
9.2(0.37)
9.15,9.19
Table II-Sensitivity, Specificity, Positive and Negative Predictive Values for Different 
Cut off Values of Mid-arm Circumference
Mid-arm
Circumference
(cm)
 Number(%) of newborns
by birth weight(g)
Sensitivity
(%)
 Specificity
(%)
 Positive
predictive
value (%)
Negative
predictive
value (%)
 
 < 2500
2500+
 
 
 
 
 
n(%)
n(%)
 
 
 
 
8.3
15 (1.2)
3 (0.2)
10.2
99.7
83.3
89.5
8.4
12 (0.9)
4 (0.3)
18.4
99.4
79.4
90.3
8.5
55 (4.3)
11 (0.9)
55.8
98.4
82.0
94.5
8.6
20 (1.6)
8 (0.6)
69.4
97.7
79.7
96.1
8.7
26 (2.0)
32 (2.5)
87.1
94.8
68.8
98.3
8.8
7 (0.6)
116 (9.1)
91.8
84.5
43.7
98.8
8.9
2 (0.2)
75 (5.9)
93.2
77.9
35.5
98.9
9.0
4 (0.3)
163 (12.8)
95.9
63.4
25.5
99.2
9.1
3 (0.2)
33 (2.6)
98.0
60.4
24.4
99.6
9.2 & above
3 (0.2)
680 (53.5)
100.0
0.0
11.6
100.0

A simple linear regression was fitted with birth weight as independent variable and MAC as dependent variable. The regression coefficient ‘b’ (slope) was 0.8218 (95% CI of b = 0.7828, 0.8607; P < 0.001). A MAC value of 8.6 cm was seen to predict a birth weight of 2500 g (95% PI 1990 g, 3010 g). MAC of 8.7 cm was seen to predict birth weight as 2580 g (95% PI 2071 g, 3099 g).

Discussion

To detect a birth weight of < 2500 g, various studies have proposed different values of MAC as a cut off point. These, as studied in different settings, were 8.6 cm (7,12), less than 9.0 cm(11) and 9.0 cm(10). At any cut off level some false negatives as well as false positives are bound to occur. However, the cut off point


Fig. 1. Receiver operating characteristics curve to choose the optimal cut-off point of mid-arm circumference. The points represent the sensitivity and 1-specificity for each vale of MAC. The MAC point which is nearest to upper and outer corner in the chart i.e., 8.7 cm is the optimal cut off point.

that gives the optimal level of false negatives and false positives can be easily found out from the ROC curve. This point happens to be the MAC of 8.7 cm with a sensitivity of 87.1% and a specificity of 98.5%. Further lowering of the cut off point to 8.6 cm results in missing out of 26 LBW cases. Since the condition being screened is a life threatening one it may not be desirable to miss as many low birth weight cases. Raising the cut off point to 8.8 cm increases the sensitivity to 97.9% and also lowers the specificity to 60.4% adding 116 false positives requiring re-screening.

The rationale of using MAC to predict birth weight is further evaluated by fitting a regression line based on the sample data. A MAC value of 8.6 cm is seen to predict a birth weight of 2500 g (95% PI 1990 g, 3010 g). It also means that just by sampling variation a value of birth weight could be as low as less than 2000 g. MAC value of 8.7 cm definitely excludes newborns with birth weight < 2000g. A birth weight of 2000 g is considered as a more appropriate criteria for defining low birth weight among Indian population(13). Based on the present study a cut off point of MAC of 8.7 cm appears to be appropriate as a general guideline.

Contributors: SLS conceptualized research question for the study and collected the data. GSS provided statistical and methodological advice and carried out statistical analysis. CGW helped in conceptualization and provided guidance and critical analysis. GSS shall act as guarantor for the study.

Funding: None.

Competing interests: None stated.

 

Key Messages

• Measurement of Mid Arm Circumference (MAC) is simple and valid method of screening for low birth weight in the newborns.

• MAC value of 8.7 cm predicts a birth weight of 2580 g (95% PI 2071 g, 3099 g) and it definitely excludes newborns with birth weight < 2000 g.

 

 

 References


1. WHO Geneva. Development of indicators for monitoring progress towards "Health for All by year 2000". " Health For All" Series No.4, WHO, Geneva, 1981.

2. Kapoor KS. How to identify low birth weight in community. Bull National Neonatal Forum. 1982; 2: 123.

3. Kumar V, Datta N. Birth weight as an indicator of health. Indian Pediatr 1984; 21: 113-118.

4. Ramji S, Marwah J, Satyanarayan L, Kapahi V, Manmohan, Bhangava SK. Neonatal thigh

circumference as an alternative indicator of low birth weight. Indian J Med Res 1986; 83: 653-654.

5. Lindt JB. Measuring acute malnutrition - A need to redefine cut off points for arm circumference. Lancet 1985; 2: 1229-1230.

6. Vaquera MDV, Touse Torch JW, Aroga J, Lechtiz A. The relationship between MAC at birth and early maturity. J Trop Pediatr 1983; 29: 164-174.

7. Bhargav SK, Ramji S, Kumar K, Manmohan, Marwah J, Sachdev HPS. Mid arm and chest circumference at birth as predictors of low birth weight and neonatal mortality in the community. BMJ 1985; 291: 1671-1679.

8. Sackett DL, Haynes RB, Tugwell P. Interpretation of diagnostic data. In: Clinical Epidemiology - A Basic Science for Clinical Medicine, 1986, Little Brown and Company, Boston, pp. 79-100, 106-198.

9. Daniel WW. Using the regression equation. In: Biostatistics: A foundation for analysis in the health sciences, 3rd Edition, John Weily & Sons, New York, 1983; pp 289-290.

10. Brenda L, Lechtis A, Klean ER. Anthropometric indicators of low birth weight. J Trop Pediatr 1985; 31: 301-305.

11. Singh MP, Devrani VK, Anandalakshmi AK, Sundaram PN. Simple tricoloured measuring tape for identification of low birth weight babies by community health workers. Ann Trop Pediatr 1988; 8: 87-91.

12. Sharma JN, Sharma BS, Gupta ML, Saxena R, Sharma V. Mid arm circumference at birth as predictor of low birth weight babies and early neonatal mortality. Indian Pediatr 1986; 23: 15-19.

13. Singh M. Care of the Newborn. New Delhi, Sagar Publications, 2000; pp 224-244.

 

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