Anthropometric measurements can identify small for gestational age newborns: a cohort study in rural Tanzania

Abstract

Background: Small-for-gestational-age (SGA) is associated with increased neonatal mortality and morbidity. In low and middle income countries an accurate gestational age is often not known, making the identification of SGA newborns difficult. Measuring foot length, chest circumference and mid upper arm circumference (MUAC) of the newborn have previously been shown to be reasonable methods for detecting low birth weight (< 2500 g) and prematurity (gestational age < 37 weeks). The aim of this study was to investigate if the three anthropometric measurements could also correctly identify SGA newborns.

Methods: In the current study from a rural area of northeastern Tanzania, 376 live newborns had foot length, chest circumference, and MUAC measured within 24 h of birth. Gestational age was estimated by transabdominal ultrasound in early pregnancy and SGA was diagnosed using a sex-specific weight reference chart previously developed in the study area. Receiver operating characteristic curves were generated for each of the anthropometric measurements and the area under the curve (AUC) compared. Operational cutoffs for foot length, chest circumference, and MUAC were defined while balancing as high as possible sensitivity and specificity for identifying SGA. Positive and negative predictive values (PPV and NPV) were then calculated.

Results: Of the 376 newborns, 68 (18.4%) were SGA. The AUC for detecting SGA was 0.78 for foot length, 0.88 for chest circumference, and 0.85 for MUAC. Operational cut-offs to detect SGA newborns were defined as ≤7.7 cm for foot length, ≤31.6 cm for chest circumference and ≤ 10.1 cm for MUAC. Foot length had 74% sensitivity, 69% specificity, PPV of 0.35 and NPV of 0.92 for identifying SGA. Chest circumference had 79% sensitivity, 81% specificity, PPV of 0.49 and NPV of 0.95 for identifying SGA. Finally, MUAC had 76% sensitivity, 77% specificity, PPV of 0.43 and NPV of 0.94 for identifying SGA.

Conclusion: In a setting with limited availability of an accurate gestational age, all three methods had a high NPV and could be used to rule out the newborn as being SGA. Overall, chest circumference was the best method to identify SGA newborns, whereas foot length and MUAC had lower detection ability.

Trial registration: Clinicaltrials.gov ( NCT02191683 ). Registered 2 July 2014.

Keywords: Africa; Chest circumference; Foot length; Gestational age; Mid upper arm circumference; Positive and negative predictive value; Small for gestational age.

Conflict of interest statement

Authors’ information

Not applicable

Ethics approval and consent to participate

Ethical approval was granted by the Medical Research Coordinating Committee of the National Institute for Medical Research in Tanzania (reference number NIMR/HQ/R.8a/Vol. IX/1717). All study participants gave written informed consent (or thumbprints from illiterate women) before enrolment. All study participants were given unique identification numbers to ensure anonymity, and only authorized personnel had access to the data. All project activities were conducted in accordance with Good Clinical Practice and the Declaration of Helsinki. Participants were assisted by the project in obtaining the best local medical care available if a disease was diagnosed during the study period.

Consent for publication

Permission to publish has been granted by the National Institute for Medical Research in Tanzania.

Competing interests

The authors declare that they have no competing interests.

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Figures

Fig. 1

Flow chart of the study population

Fig. 2

Association between foot length, chest circumference and MUAC vs. birth weight and gestational age at delivery

Fig. 3

ROC curves for detecting SGA, low birth weight and prematurity, respectively using the three anthropometric measurements