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Logo of mjafiGuide for AuthorsAbout this journalExplore this journalMedical Journal, Armed Forces India
Med J Armed Forces India. 2003 January; 59(1): 84.
Published online 2011 July 21. doi:  10.1016/S0377-1237(03)80129-6
PMCID: PMC4925773

Maternal Haemoglobin and Birth Weight

Dear Editor,

I read with interest the article on maternal haemoglobin and birth weight in the April 2001 issue of the journal [1]. I request a few clarifications from the authors to help me understand the study better:

  • (a)
    Type of study: The study cannot be “cross-sectional” and “prospective” at the same time since the first type of study investigates subjects on one occasion only whereas in the second type, subjects are followed forward in time [2].
  • (b)
    Study population: It is said to be a “stratified random study”. The following need clarification :-
    • (i) Randomization is only applicable to interventional studies; this was an observational one;
    • (ii) If this study was of the cohort type where pregnant women were observed for their haemoglobin (Hb) levels forward in time and the outcome of interest was birth weight, then the authors have sub-divided the cohort based on socio-economic status at the outset. This is an accepted procedure but does not amount to “stratified randomization” [2];
    • (iii) If what the authors wanted to convey, was that the 1000 study subjects were randomly selected from the entire population of available pregnant women then the total number of pregnant women who were eligible for enrolment in the study and the method employed for random selection should have been mentioned;
    • (iv) The study subjects were not stratified based on the inclusion/exclusion criteria as stated in Material and Methods. They were stratified based on their socio-economic status;
    • (v) Did all the 1000 pregnant women go on to deliver live infants?

Were there no still births in this cohort? The number of infants born to these 1000 women is not mentioned anywhere!

Clarification on the above is important because of the mothers of 1000 liveborn infants were interviewed and their records studied, then this becomes a retrospective case-control study.

  • (c)
    Multiple pregnancy, inter-pregnancy interval and chronic malaria are known to influence birth weight but find no mention in the inclusion / exclusion criteria.
  • (d)
    The second objective of the study was to analyze if maternal anaemia influences fetal outcome in terms of birth weight. The following need clarification:
    • (i) The authors have not defined criteria used in this study for the diagnosis of anaemia;
    • (ii) No correlation between “anaemia” and birth weight has been presented in the results section (correlation between haemoglobin and birth weight is the first objective of this study and not the same as the above)
    • (iii) From the author's declaration of 51.4% prevalence of anaemia in this study and Figure 1, it is deduced that a maternal Hb value <11.0 gm/dL was taken as anaemia. How was this figure selected? Was a single value below 11.0 taken to denote anaemia?
    • (iv) Since minor differences of Hb are significant in this study, was the method of Hb estimation in the two hospitals same and standardized?
  • (e)
    Conducting a study of this magnitude is not at all easy and the authors deserve kudos for the effort. This study could also have been utilised to look into the relationships between:
    • (i) Duration of maternal anaemia and birth weight;
    • (ii) Trimester-wise timing of maternal anaemia and birth weight; and,
    • (iii) Morphology of anaemia and birth weight.


1. Raghuraman TS, Parimala V, Bhalla M, Venkateshwar V, Iyengar A. A correlative study of maternal haemoglobin and birth weight. MJAFI. 2001;57:110–113.
2. Altmann DG. Practical statistics for medical research. Chapman and Hall; London: 1991. pp. 91–92.

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