Reductions in stillbirths and preterm birth in COVID-19 vaccinated women: a multi-center cohort study of vaccination uptake and perinatal outcomes
Authors: Hui Lisa , Marzan Melvin Barrientos , Rolnik Daniel L. , Potenza Stephanie , Pritchard Natasha , Said Joanne M. , Palmer Kirsten R , Whitehead Clare L. , Sheehan Penelope M. , Ford Jolyon , Mol Ben W. , Walker Susan P. 
Published: July 2022

Background

COVID-19 infection in pregnancy is associated with a higher risk of progression to severe disease, but vaccine uptake by pregnant women is hindered by persistent safety concerns. COVID-19 vaccination in pregnancy has been shown to reduce stillbirth, but its relationship with preterm birth is uncertain.

Objective

The aim of this study was to investigate the sociodemographic characteristics associated with vaccine uptake in Melbourne, Australia, and to compare perinatal outcomes by vaccination status.

Study design

Retrospective multicenter cohort study in Melbourne following the national recommendations for mRNA COVID-19 vaccination during pregnancy in June 2021. Routinely collected data from all 12 public maternity hospitals in Melbourne were extracted on births ≥ 20 weeks’ gestation from 1st July 2021 to 31 March 2022. Maternal sociodemographic characteristics were analyzed from the total birth cohort. Perinatal outcomes were compared between vaccinated and unvaccinated women for whom weeks 20-43 of gestation fell entirely within the 9-month data collection period. The primary outcome was the rate of congenital anomaly in singleton infants ≥ 20 weeks’ gestation among women vaccinated during pregnancy. Secondary perinatal outcomes including stillbirth, preterm birth (spontaneous and iatrogenic), birthweight ≤ 3rd centile, and newborn intensive care unit admissions were examined for singleton infants ≥ 24 weeks’ gestation without congenital anomalies. We calculated the adjusted odds ratio of congenital anomalies and perinatal outcomes among vaccinated versus unvaccinated women using inverse propensity score weighting regression adjustment with multiple covariates; p< 0.05 was considered statistically significant.

Results

Births from 32,536 women were analyzed: 17,365 (53.4%) were vaccinated and 15,171 (47.6%) were unvaccinated. Vaccinated women were significantly more likely to be older, nulliparous, non-smoking, not requiring an interpreter, of higher socioeconomic status, and vaccinated against pertussis and influenza. Vaccination status also varied by region of birth: compared with women born in Australia, women born in South and Eastern Europe, the Middle East, Africa and Oceania had lower adjusted odds of vaccination. There was no significant increase in the rate of congenital anomalies or birth weight ≤ 3rd centile in vaccinated women. Vaccinated women were significantly less like to have an infant with a major congenital anomaly compared with the unvaccinated group (2.4% vs 3.0%, aOR 0.72, 95%CI 0.56-0.94, p=0.02). This finding remained significant even when the analysis was restricted to women vaccinated before 20 weeks’ gestation. Vaccinated women had a significantly lower rate of stillbirth (0.2% vs 0.8%, aOR 0.18, 95%CI 0.09-0.37, P < 0.001. Vaccination was associated with a significant reduction in total preterm births < 37 weeks (5.1% vs 9.2%, aOR 0.60, 95% CI 0.51-0.71, p< 0.001), spontaneous preterm birth (2.4% vs 4.0%, aOR 0.73 95% CI 0.56-0.96, p=0.02) and iatrogenic preterm birth (2.7% vs 5.2%, aOR 0.52, 95%CI 0.41-0.65, p< 0.001).

Conclusions

COVID-19 Vaccine coverage was significantly influenced by known social determinants of health, which is likely to influence the strong association between COVID-19 vaccination and lower risks of stillbirth and preterm birth. We did not observe any adverse impacts of vaccination on fetal growth or development.

AT A GLANCE

Why was this study conducted?

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COVID-19 infection in pregnancy is associated with a higher risk of progression to severe disease, but vaccine uptake by pregnant women is hindered by persistent safety concerns. COVID-19 vaccination in pregnancy has been shown to reduce stillbirth, but its relationship with preterm birth is uncertain.

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Most of the published literature on COVID-19 vaccination in pregnancy have methodological limitations including fixed cohort bias and time-varying exposure.

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We conducted this multicenter study to provide robust evidence on mRNA COVID-19 vaccination and perinatal outcomes including congenital anomalies, stillbirth, and preterm birth.

What are the key findings?

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The adjusted odds of stillbirth, preterm birth, and neonatal intensive care admission were significantly reduced among infants born to COVID-19 vaccinated women compared with unvaccinated women. COVID-19 vaccination during pregnancy was not associated with an increase in congenital anomalies.

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Our results conclusively demonstrate a significant reduction in both spontaneous and iatrogenic preterm birth for vaccinated women

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Vaccinated women were significantly more likely to be older, nulliparous, non-smoking, not requiring an interpreter, residing in a higher socioeconomic postcode, and vaccinated against pertussis and influenza. There were also significant differences in vaccination rates by region of birth.

What does this study add to what is already known?

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Our analysis confirmed a strong relationship between the COVID-19 mRNA vaccine and lower preterm births and stillbirths

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In addition to its impact on reducing severe COVID-19 illness, vaccination may be a proxy for other biological and social determinants of health among our pregnant population.