COVID-19 incidence in women of reproductive age: a population-based study in Reggio Emilia, northern Italy

BACKGROUND: Despite being at higher risk of severe disease and pregnancy complications, evidence on susceptibility to SARS-CoV-2 infection in pregnancy is still limited. The aim of the study is to compare the likelihood of undergoing a SARS-CoV-2 test and testing positive for COVID-19 in pregnancy and puerperium with that of the general female population of reproductive age. METHODS: This is a retrospective population-based cohort study including 117,606 women of reproductive age (March 2020-September 2021) with 6608 (5.6%) women having ≥ 1 pregnancy. Women were linked to the pregnancy registry to be classified as “non-pregnant”, “pregnant”, and “puerperium”; then, according to the national case-based integrated COVID-19 surveillance system, all women undergoing a SARS-CoV-2 test during the study period were identified. The Incidence Rate Ratio was calculated to compare the likelihood of being tested for SARS-CoV-2 in pregnant, puerperium and non-pregnant women among all women included. The likelihood of having a COVID-19 diagnosis was calculated using two comparators (not-pregnant women and the person-time before/after pregnancy) by means of Cox proportional hazards models, adjusting for age and with the cluster option to control standard error calculation in repeated pregnancies. Only first infection and swabs before the first one positive were included. RESULTS: The probability of being tested for SARS-CoV-2 was 4.9 (95% CI: 4.8–5.1) and 3.6 times higher (95%CI: 3.4–3.9) in pregnancy (including spontaneous miscarriages) and in the puerperium, respectively. The Hazard Ratio (HR) of covid-19 diagnosis during pregnancy vs. non-pregnancy was 1.17 (95% CI 1.03–1.33) with similar results when comparing the risk during pregnancy with that of the same women outside pregnancy (puerperium excluded), with an HR of 1.13 (95% CI 0.96–1.33); the excess decreased when excluding the test performed at admission for delivery (HR 1.08 (95%CI 0.90–1.30). In the puerperium, the HR was 0.62 (95% CI 0.41–0.92) comparing women with ≥ 1childbirth with all other women and excluding the first two weeks of puerperium. CONCLUSIONS: Women during pregnancy showed a small increase in the risk of infection, compatible with a higher likelihood of being tested. A lower probability of infection during the puerperium was observed during the entire pandemic period, suggesting likely protective behaviors which were effective in reducing their probability of infection.