1. Small for gestation age (SGA) infants are anatomically and physiologically distinct from appropriate for gestational age (AGA) infants [2]. However in our study, on calculating regression equation predicting insertional length (IL, in cm) from the weight (kg) among AGA and SGA neonates, the results remained similar (both regression coefficient and intercept) as follows:

　　IL (overall population, cm) = wt (kg) +4.95

　　IL (AGA population, cm) = 1.1×wt (kg) +4.928

　　IL (SGA population, cm) = 1.1×wt (kg) +4.922

2. We accept that the sample size required in different groups (calculated post hoc from our results) is more than the number of infants enrolled. However, there was no prior study that had reported gestation or weight-based normograms of optimally placed endotracheal tube on ultrasound to guide us. Therefore, we conducted a pilot study on 15 infants in two weight categories. To derive adequate sample size in five weight categories and four gestation categories, a pilot study would require about 80-100 infants, which was not feasible for us.

3. Median (IQR) day of enrollment of the neonates was 3 (1-9) days. None of the study subjects had cephalhematoma or subgaleal bleed. Neonates with caput succedaneum enrolled on day 1 had their head circumference measurement repeated after 48 hours of life, not only for our study but also as a standard clinical protocol because resolution of caput succedaneum takes few days [3]. We agree that our study had male preponderance and the possibility of calculating sex-specific normative data of optimally placed endotracheal tube on ultrasound based on adequate sample size needs to be explored.