University of Dublin (Trinity College), St Jamess Hospital, Dublin 8, Ireland. E-mail:kabirz{at}tcd.ie
SirI read with interest the useful pages devoted to birthweight in the recent issue of the International Journal of Epidemiology all over again.13 Although it was difficult to comprehend the mathematical implication of the mortality analysis, the overall conclusion appeared to be justified. However, I wonder if Wilcoxs framework answered all the questions related to a global birthweight distribution or was it tailor-made to the better-off populations. I failed to figure out this element of bias in the context of global population or was it anyway connected with the worsening perinatal risk in the West4 across different population groups, as commented upon by Wilcox. This creates scepticism for me with regard to low birthweight (LBW) distribution in the rest of the 90% of the global population, the less-developed nations in particular, which was not adequately addressed in any of the articles cited.13
As rightly pointed out, the universal application of the LBW figure of <2500 g is questionable, particularly when there are epidemiological-demographic transitions world-wide. It is important to address an alternative approach to LBW as a surrogate indicator of population risk for those in the less-developed nations. The approaches discussed by Wilcox may have limited applications to the majority of these nations. First, most of these nations have neither ready access to a computer to utilize the user-friendly statistical software across all levels of health care, unlike the West, nor do they have a robust health information system, despite the free distribution of birthweight data. Second, the majority of mothers are from rural areas and have very little or no formal education, and this rules out the application of gestational-age estimation based on LMP (last menstrual period). Moreover, recent technologies, such as ultrasonographic estimation, are madness in these nations. Intrauterine growth retardation and the rest of the approaches were equally handicapped in light of Wilcoxs explanation.
To reiterate, the mean birthweight of an Indian baby, for instance, is 2900 g compared with 3500 g for a Swedish baby.5 Based on Wilcoxs framework, this may shift the mean birthweight distribution curve in India to the left, consequently increasing the residual population and indicating a high per cent of small pre-term births at risk. If I am not wrong, I doubt whether this particular observation is apparent in reallife situations with regard to the Indian population at an aggregate level. On the other hand, the average LBW rate (mostly comprising small term babies) in India has been hovering around 25% over the past decade,6 as opposed to a considerable improvement in all the child mortality rates, including perinatal and neonatal mortality rates, during the same period.7 Interestingly, this simple observation appears to address some of the important issues highlighted in Wilcoxs long-winded analysis.
More importantly, health resources are limited in less-developed nations which was not taken into account in the analysis. A crude indicator, such as a fixed cut-off of <2500 g not only identifies a higher proportion of small term babies with better survival but is also telling on the inefficient health care system in these regions. Paradoxically, adjustment for the birthweight-specific mortality distribution is difficult for the reasons mentioned earlier. So where do we go from here? If Irvas3 final part of birthweight being causal is true, does a lower cut-off for LBW help identify the high risk babies more accurately, timely, efficiently or equitably in such a situation? This cost-effective approach may be an over-simplification of the controversies surrounding birthweight as an epidemiological endpoint. To my mind, this ordinary hypothesis offers a rich opportunity for further investigation, possibly without using any special analytical techniques. Nonetheless, a future refinement in the existing indicator would help public policy initiatives to be appropriately targeted, and preferentially channel the limited health resources in reducing the health inequity world-wide. It would be worth observing whether size really matters at the end of the day!
References
1 Wilcox AJ. On the importanceand the unimportanceof birthweight. Int J Epidemiol 2001;30:123341.
2 David R. Commentary: Birthweights and Bell Curves. Int J Epidemiol 2001;30:124143.
3 Hertz-Picciotto I. Commentary: When brilliant insights lead astray. Int J Epidemiol 2001;30:124344.
4 Barros FC, Victoria CG, Vaughan JP et al. The epidemiological transition in maternal and child health in a Brazilian city, 198293: a comparison of two population-based cohorts. Paediatr Perinat Epidemiol 2001;15:411.[CrossRef][ISI][Medline]
5 National Center for Health Statistics. Advance Report of Final Natality Statistics, 1991. Monthly Vital Statistics Report, Vol. 42, No. 3, Suppl. Hyattsville, MD: Public Health Service, 1993.
6 UNICEF statisticsend decade databaseslow birth weight (internet communication http://www.childinfo.org/eddb/lbw/index.htlm. Accessed on 09/04/2002).
7 Ministry of Home Affairs. Compendium of Indias Fertility and Mortality Indicators 19711997. New Delhi: Sample Registration System, Registrar General India, 1999.