Dear Editor,

We read the paper by Pathirana et al.^{Reference Pathirana, Lassi and Roberts1} with interest. The authors performed a large meta-analysis to determine cardiovascular risk factors in offspring exposed to gestational diabetes mellitus (GDM) in utero. They concluded that offspring exposed to GDM have elevated systolic blood pressure, body mass index, and glucose. Those exposed to GDM in utero may benefit from early childhood blood pressure measurements. This finding has implications for the generalization of trial results to the broader patient population and for future trial design. After carefully reading, we wish to put forth the following suggestions.

Repeatedly including the same study population will affect the total sample size and the number of participants in each group; thus, duplicated studies using the same study population should not be included in a meta-analysis. However, in Table 1, we found that the studies in references 21^{Reference Tam, Ma and Yang2} and 15^{Reference Tam, Ma and Yang3} were conducted by the same group of authors, with participants from the same site and with similar baseline characteristics. Hence, we suspect that these are duplicate studies. Similarly, references 43^{Reference Vohr, McGarvey and Garcia Coll4} and 44^{Reference Vohr, McGarvey and Tucker5}, 38^{Reference Krishnaveni, Hill and Leary6} and 18^{Reference Krishnaveni, Veena, Hill, Kehoe, Karat and Fall7} are duplicates. This will affect the credibility of the result. Although these studies have low weights in the summary estimates, it is a matter of principle. The author should formulate strict inclusion and exclusion criteria, exclude repeated literature using the same study as a whole, and select the literature with the best quality or the largest sample size for analysis.