Lack of association between COVID-19 vaccines and miscarriage onset using a case-crossover design.

Publication date: Mar 27, 2024

Pregnant women might have an increased risk of SARS-COV-2 infection. Although evidence towards the efficacy and safety of COVID-19 is growing still there is room for improvement on the knowledge towards pregnancy adverse events, such as miscarriage. We explored the association of COVID-19 vaccine with the risk of miscarriages using the Real-World. We identified a cohort of vaccinated pregnancies using the BIFAP database which contains systematically recorded data on care patients in Spain (Nā€‰=ā€‰4054). We then restricted it to those women who had a miscarriage using a validated algorithm (Nā€‰=ā€‰607). Among them, we performed a case-crossover design to evaluate the effect of intermittent exposures on the risk of miscarriage. Adjusted Odds Ratio with their confidence intervals were calculated using two analytical approaches: conditional logistic regression and Generalized Linear Mixed-Effects Models. A total of 225 (37. 1%) were aged 35-39 years. The most common comorbidities were asthma, migraine, gastritis, and hypothyroidism. A total of 14. 7% received only one dose of COVID-19 and 85. 3% two doses, respectively. A total of 36. 8% of women with one dose and 27. 6% with two doses received the vaccine 7 days prior to the miscarriage. Corresponding adjusted estimates for the risk of miscarriage using the conditional logistic regression where as follows: 1. 65 (95% CI 0. 85-3. 23) when using as the sum of 3 control moments among women with one dose, 1. 02 (95% CI 0. 72-1. 46) among women with two doses and 1. 03 (95% CI 0. 72, 1. 46) using the whole study population. Very similar results were obtained when conducting the Generalized Linear Mixed-Effects Models. There was no overall increased risk of miscarriage onset associated with COVID-19 vaccine although contradictory results were found according to the number of doses. Further studies are required with larger sample sizes to assess this association.

Open Access PDF

Concepts Keywords
Conducting Case-crossover study
Database COVID-19 vaccine
Migraine Epidemiology
Pregnancy Miscarriage
Spain Obstetrics


Type Source Name
disease VO LACK
disease MESH COVID-19
disease MESH miscarriage
disease VO pregnant women
pathway REACTOME SARS-CoV-2 Infection
disease VO COVID-19 vaccine
disease VO vaccinated
disease IDO algorithm
disease MESH asthma
pathway KEGG Asthma
disease MESH migraine
disease MESH gastritis
disease MESH hypothyroidism
disease VO dose
disease VO vaccine
disease VO population
drug DRUGBANK Coenzyme M
disease VO Algenpantucel-L Vaccine
disease VO Colorectal cancer DNA vaccine pCEA/HBsAg encoding carcinoembryonic antigen and hepatitis B surface antigen
disease MESH death
disease MESH alcohol abuse
disease MESH infection
disease VO Hormone
disease MESH preterm birth
disease VO vaccination
disease MESH thrombosis
disease MESH thrombocytopenia
disease MESH anomalies
disease VO inactivated influenza vaccine
disease VO Gap
drug DRUGBANK Pentaerythritol tetranitrate
drug DRUGBANK Phencyclidine
disease VO laboratory test
drug DRUGBANK Timonacic
disease VO protocol
disease MESH lifestyle
disease MESH pregnancy outcome
disease MESH pregnancy complications
disease MESH stillbirth
disease VO time
disease IDO history
disease MESH obesity
disease MESH anemia
disease MESH hypertension
disease MESH multiple sclerosis
disease MESH deep venous thrombosis
disease MESH pulmonary embolism
disease MESH COPD
disease MESH epilepsy
disease MESH psoriasis
drug DRUGBANK Acetaminophen
drug DRUGBANK Ergotamine
drug DRUGBANK Serotonin
disease MESH ischemic heart diseases
disease IDO immunodeficiency
disease VO age
disease MESH Arrhythmia
disease VO immunization
disease MESH influenza
disease VO Papillomavirus vaccine
disease VO unvaccinated
drug DRUGBANK Indoleacetic acid
disease MESH morbidity
disease MESH diabetes mellitus
disease MESH chromosomal abnormalities
disease MESH syndrome
drug DRUGBANK Empagliflozin
disease MESH heart failure
disease VO frequency
disease VO efficiency
disease MESH birth defects
disease VO vaccine candidate
disease VO Ad26.COV2.S
disease VO influenza vaccines
disease VO Optaflu
disease VO coronavirus vaccine
disease VO effectiveness
disease IDO cell

Original Article

(Visited 1 times, 1 visits today)