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Estimation of the causal effect of sex on neonatal intensive care unit outcomes among very low birth weight infants

Journal of Perinatology (2024)Cite this article

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Abstract

Objective

Estimate the causal effect of sex on outcomes in the neonatal intensive care unit (NICU) among very low birth weight (VLBW) infants.

Study design

Retrospective cohort study using Vermont Oxford Network data to compare NICU outcomes for VLBW males versus females. Odds ratios (OR) for outcomes that differed significantly by sex were computed using standard unweighted analysis and inverse probability weighted (IPW) analysis to correct for selection bias.

Results

Using standard analysis, males were significantly more likely to die before discharge and experience six other adverse outcomes. From IPW analysis, male sex caused a 56% increase in the odds of death before discharge (OR = 1.56, 95% confidence interval: 1.18–1.94). Standard unweighted results were significantly biased towards increased risk of adverse outcomes for males (p = 0.005) compared to IPW results for which three outcomes were no longer significantly associated with male sex.

Conclusion

Standard statistical methods generally overestimate the casual effect of sex among VLBW infants.

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Fig. 1: Scatterplot of GA versus BW.
Fig. 2: DAGs depicting assumed casual relationships between sex, BW, GA, unmeasured covariates and outcomes.

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Data availability

Study data was obtained from, and all data definitions were governed by the Vermont Oxford Network (VON). The dataset analyzed for the current study is not publicly available due to IRB and VON policies that strictly protect the data as privileged and confidential, but the corresponding author will make every effort to accommodate reasonable requests for information about the study data.

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Funding

Funding

No funding was received to conduct this study.

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Authors and Affiliations

  1. Baylor College of Medicine, Department of Pediatrics, Section of Neonatology, Houston, TX, USA

    Joseph L. Hagan

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  1. Joseph L. Hagan
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The study was conceived of and conducted solely by JH.

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Correspondence to Joseph L. Hagan.

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The author declares no competing interests.

Ethics approval and consent to participate

This study was approved by the Baylor College of Medicine Institutional Review Board (IRB, protocol H-51590) with a waiver of consent to participate due to the retrospective design posing minimal risks to subjects. This study was performed in accordance with the Declaration of Helsinki.

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Cite this article

Hagan, J.L. Estimation of the causal effect of sex on neonatal intensive care unit outcomes among very low birth weight infants. J Perinatol (2024). https://doi.org/10.1038/s41372-024-01989-1

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