Reduction in the preterm birth rate during the COVID-19
pandemic: analyzing causation
Giovanni Sisti1, MD, Julie T.
Joseph2, MD, MPH
1Division of Maternal-Fetal Medicine, Department of
Obstetrics and Gynecology, College of Medicine -Tucson, The University
of Arizona, 1501 N. Campbell Ave., Tucson, AZ. Electronic address:
gsisti83@gmail.com.
2Division of Infectious Diseases, New York Medical
College, Valhalla, NY, USA.
497 words
An article by Rusconi et al. in the current issue of BJOG compared
preterm birth (PTB) during the COVID-19 pandemic period (March 1, 2020,
to March 31, 2021) to the pre-pandemic period (January 2017- February
2020). Their study evaluated 1,479,301 women, covering 84.3% of the
births in Italy and noted a decreased risk of PTB (Risk Ratio: 0.91;
95% Confidence Interval, 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 of PTB might be due to a number of pandemic-related
factors including enhanced attention to health care of pregnant women, a
reduction in the number of women undergoing in vitrofertilization, 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 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 due to the presence of multiple variables that can introduce
bias and other errors (Elvik R. Accid Anal Prev. 2013;60:245-53). In
addition, as noted for research in obstetrics, “association is not
causation” (Skupski D, 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 and the availability of
detailed outcome records, 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 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
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 due, for example, at least in part to the
general improvement in obstetric care over time, rather than being a
consequence of the COVID 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, while 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.