Reduction in preterm birth rate during the COVID‐19 pandemic: Analysing causation

Short abstract

Linked article: This is a mini commentary on Rusconi et al., pp.276–284 in this issue. To view this article visit https://doi.org/10.1111/1471‐0528.17315

An article by Rusconi et al. in the current issue of BJOG compared preterm birth (PTB) during the COVID‐19 pandemic period (from 1 March 2020 to 31 March 2021) with PTB in the pre‐pandemic period (from January 2017 to February 2020). Their study evaluated 1 479 301 women, covering 84.3% of the births in Italy, and noted a decreased risk of PTB (RR 0.91, 95% CI 0.88–0.93) and no change in the rate of stillbirth during the COVID‐19 pandemic period. The authors hypothesized that this reduction in PTB might be the result of a number of pandemic‐related factors, including enhanced attention to the health care of pregnant women, a reduction in the number of women undergoing in vitro fertilization, increased emphasis on a healthy diet and a diminished exposure to air pollution. Previous studies on alterations in the rates of PTB and stillbirth during COVID‐19, including reviews and meta‐analyses, have yielded conflicting results, and a consistent trend has not been identified. The present investigation adds support to the view that the increased attention given to pregnant women during the pandemic may have resulted in unforeseen benefits. The inclusion of twins in their analysis adds an additional parameter to these studies.

It is difficult to conduct an unambiguous analysis of changes in trends over time because of the presence of multiple variables that can introduce bias and other errors (Elvik Accid Anal Prev 2013;60:245–53). In addition, as noted for research in obstetrics, ‘association is not causation’ (Skupski Am J Obstet Gynecol 2016;214:133–4). We must be cautious before accepting definitive results from individual studies and every possible source of bias must be carefully considered. The study by Rusconi et al. employed a very large sample size with detailed outcome records readily available, supporting the reasonableness of their observations. However, questions concerning the ambiguity of their conclusions are unavoidable. For example, the study did not evaluate trend‐rate analysis bias. The two time periods compared are continuous: the first ended in February 2020 and the second began in March 2020. Pregnancies that were initiated and completed within the pandemic period might not be affected in the same way as pregnancies that began prior to the pandemic but ended during the first months of the pandemic. The absence of an exclusionary time period between the pandemic and the pre‐pandemic periods, to allow for the removal of overlapping cases, remains a shortcoming of their investigation. There is also a failure to account for a possible secular trend as a source of bias. The difference between groups might be linked, at least in part, with the general improvement in obstetric care over time, rather than being a consequence of the COVID‐19 pandemic. Investigators at the National Institutes of Health recently commented on the difficulty in making valid associations between a SARS‐CoV‐2 infection and the occurrence of various pathologies (https://www.nhlbi.nih.gov/news/2021/unraveling‐mysteries‐covid‐19).

In summary, although an association is plausible, it remains problematic to definitively conclude that the COVID‐19 pandemic had a direct positive effect on the rate of PTB in Italy.

CONFLICT OF INTERESTS

None declared. Completed disclosure of interests form available to view online as supporting information.

Supporting information

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DATA AVAILABILITY STATEMENT

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.