Circumference as an Alternative to Birth Weight for Identification of Low
Low birth weight (LBW) infants run a higher risk of morbidity and mortality in the perinatal period(1). In our country where almost 70-80% births take place at home and peripheral hospitals, taking accurate birth weight is a problem due to unavailability of weighing scale and trained personel. Hence there is a constant search for newer methods to detect LBW babies so that early intervention can be instituted. Various authors have used different surrogate anthropometric measurements from different parts of our country (2-4). There are no such studies from eastern India. Hence, an attempt was made to validate the feasibility of using calf circumference as a predictor of LBW babies.
The study included 1580 consecutively delivered neonates (620 LBW babies) at the Obstetric and Gynecological ward of V.S.S. Medical College Hospital, Burla from January 1997 to December 1998. The birth weight (wt), crown heel length (CHL), crown rump length (CRL), head circumference (HC), chest circumference (CC), midarm circum-ference (MAC), thigh circumference (TC) and calf circumference (CC) were measured by standard techniques. All the meausrements were taken by a single person (AKS) through out the study period within 24 hours of delivery. Nude weight of the baby was taken in a beam balance scale to the nearest 20gm. CHL and CRL were measured by a fibreglass tape in infantometer. HC was measured by putting the tape anteriorly at glabella and posteriorly along with the most prominent point. Chest circumference was measured at the level of xiphoid cartilage. Midarm circum-ference was measured midway between acromion process and olecranon process of left arm. Thigh circumference was measured at the lowest furrow of gluteal region.
Calf circumference was measured at the most prominent point in the semiflexed posi-tion of the leg. All the measurements were taken nearest to 0.1 cm. Standard statistical methods were adopted for determination of critical limit, sensitivity, specificity and cor-relation matrix(r) of different anthropometric measurements in relation to birth weight.
LBW prevalence was 39.2%. For determining a birth weight of 2500 gram, the critical limits of calf circumference (CC) was £9.9cm (95%, CI 8.7-12.5 cm). Critical limits for CHL, CRL, HC, CC, MAC and TC were £44.6 cm, £29.8 cm, £33.9 cm, £31.8 cm, £8.3 cm and £13.9 cm, respectively (Table I). Using the above critical limits the highest sensitivity for detecting LBW babies was seen with CC (85.2%), followed by TC (83.3%). The specificity of CC and TC were almost equal to TC (83.9%) and CC (82.5%) for newborns above 2500 g. Using correlation matrix(r) it was observed that though all measurements showed significant correlation with birth weight, the highest order of correlation was found with CC (0.78) followed by TC (0.75).
Since identification of LBW babies in rural community is of highest priority to provide effective minimal perinatal care to decrease mortality, there is a constant search for a simple and inexpensive method for screening such newborns. In the present study, a significant correlation of various anthropometric measurements was observed with birth weight. Calf circumference had the best correlation with birth weight followed by thigh circumference as was observed by others(3,4). With calf circumference of 10 cm as the cut off point, almost 95% LBW babies can be identified with fair degree of accuracy.
In conclusion calf circumference meausrement at birth can be used as a simple, reliable and cost effective method of identi-fying risk neonates in the community by peripheral workers.
Contributors: GCS conceived the idea, supervised data collection and helped in analysis and drafting; he will act as the guarantor. AKS was responsible for data collection and analysis.