Assessment of the reference values of intrauterine growth with particular to ponderal index for our region

Introduction: Ponderal index (PI) is well known growth parameter from birth onwards but there are no reference values from 25 weeks till birth. Therefore, incorporation of a combination of weight and length may be a useful parameter to assess the growth. Aims and Objectives: To set standards of ponderal indices for local population and to identify high risk vs low risk and growth difference between male and female babies. Materials and Methods: This is prospective observational study done in NIMS, Jaipur from Jan. 2015 –June 2016 with503 institutional births fulfilling the inclusion criteria of singleton born intramural births with confirmed gestational ages between 25 to 43 weeks.These babies were then tabulated according to their gestational age and sex. The mean PI, standard deviation of PI were calculated and their curves were drawn. Results: Out of 503 neonates studied, 272 (54.08%) were females and 231 (45.92%) were males. The minimum PI was seen at 28 weeks (1.98±0.10) with a gradual increase along with gestational ages. The maximum PI was at 42 weeks (2.65±0.28). No significant difference was seen in males and females. Growth velocity was maximum in earlier weeks. Sharp fluctuation in growth was seen around 30 to 33 weeks. Conclusion: Classification of neonates with the help of such growth curves is inexpensive and does not require advanced knowledge. These values for PI cannot be used as standards rather used as reference values for our region for further research.


Introduction
Gestational age and birth weight are important factors of growth, development and survival of the child [1]. Growth of fetus is dependent on maternal, placental, and geneticfactors. Morbidity and mortality in newborns are directly correlated with gestational age and weight.
The anthropometric measures of length, birth weight and certain circumferences in addition to period of gestation are expected to provide the building blocks for the desired index [2]. Ponderal index (PI) has been mentioned as growth parameter from birth onwards. But it is irony that there are no standards for its measurement in babies in whom the growth is fastest during the intrauterine life. Therefore, we decided to layout a "reference" standard of PI as a growth parameter from 25 weeks of gestation till 43weeks for our rural population and also to identify any difference in values of PI according to sex. All babies fulfilling the inclusion criteria were classified according to local curves in our setting into Small for Gastational Age (SGA), Appropriate for Gestational age (AGA) and Large for Gastational Age (LGA) babies according to their gestational ages. Examination of newborn was done at birth for weight and length.

Ponderal index (PI) = Birth weight (in kgs) x 100/Crown-heel length 3 (in metres)
These babies were then tabulated according to their gestational age and sex. The mean PI, standard deviation of PI were calculated and their curves were drawn.

Discussion
The study was designed to lay down the reference values of intrauterine growth with particular reference to PI for our region and population. The ponderal index was calculated by the following formula; Table 3 shows comparison of PI found in other studies with our study. There is a paucity of Indian published data whereas there are few foreign studies from developed countries for comparison. As can be seen the values obtained in the present study are consistently lower than the values obtained in the other studies conducted outside India due to racial, environmental, maternal and socioeconomic variations, while they show a close relation with those that were conducted in India.
Though ponderal indices were not done in other studies we have calculated it using their data of gestational age specific weight and length and then compared the results with our study. Comparing among the literature from abroad the mean values are higher for the more recent studies (Olufemi et al [3]; Fok TK et al [4]) when compared to the older ones like those given by Lubchenco et al [5] even though the background remains similar. This could be due to the larger sample sizes or better estimation of gestational ages but also could be due to the changing anthropometric values over the years as expected with rise in health standards and antenatal care. Our values fall in the higher range when compared to the study done by Purohit A et al in Rajasthan. This can be due to the fact that study was done at a tertiary referral center of the state [6]. The closest match is between the present study with Saroha H et al [7].
Our reference results for birth weight, birth length for term infants 37-42 weeks gestation are very similar to the corresponding WHO [8,9,] growth reference dataincreasing the validity of our data.Centers for Disease Control and Prevention CDC [10,11] being a developed world study have higher values at birth. Limitations of the study: The major limitation of this study is the small size of the sample population & exclusion of condition like gestational diabetes and pregnancy induced hypertension was not always possible. The nutritional statuses of the mother and the socio-economic condition of the family which may again affect the growth of the fetus have not been taken into account.
Birth weight and length increases steadily but with variable velocities so it's difficult to comment upon what affects PI and hence the fluctuation. However we need a study with a larger sample size and inclusion of all maternal factors to establish a fact behind this fluctuation.

Conclusion
The utility of growth curves in classifying the newborns at birth has been attempted. Classification of neonates with the help of such growth curves is found to be inexpensive and accurate and does not require advanced knowledge. As our values at term are similar to that of WHO, we can conclude that the values of initial weeks should be relevant, since we do not have standards to compare.
These values for preterm PI cannot be used as standards but can be used as reference values for our region for further research and use in our hospital setting to assign the babies as high risk and low risk neonates for the future reference and follow-up. What these studies add to existing knowledge? -PI is an important parameter as a growth of neonates but reference values were not established yet for different age group in intrauterine life. We want to generate fetal parameters to lay down reference values for the same.