Background. Human parvovirus B19 activity increased following the COVID-19 pandemic, triggering a U.S. Health Alert Network advisory reminding public health partners and clinicians that B19 infection during pregnancy can result in serious complications. We investigated the risk of fetal complications before, during, and after the pandemic.

Methods. We used data from PCORNet, a U.S. dataset linking standardized electronic health records. Pregnant women and fetal complications including anemia, blood transfusion, growth problem, and hydrops fetalis, were identified using ICD-10 codes. Women with B19 were identified using ICD-10 codes, positive B19 IgM, or PCR laboratory testing. Complications among B19 pregnant mothers were evaluated in 2018–19, 2021–22, and 2024–25. Risk ratios (RRs) and 95% confidence intervals (CIs) were calculated to compare complications between pregnant women with and without B19 infection within each period.

Results. The risk of pregnancy complications among pregnant women with B19 increased across periods: 5.59% (95% CI: 3.8–7.4) in 2018–19, 7.10% (4.30–9.90) in 2021–22, and 14.45% (11.83–17.07) in 2024–25. In comparison, complication risk among women without B19 was 2.36% (2.32–2.41), 1.43% (1.40–1.46), and 1.59% (1.56–1.62), across similar periods respectively. The relative risk of complications associated with B19 infection increased substantially over time: RR 2.37 (1.71–3.28),  4.97 (3.35–7.38), and 9.08 (7.56–10.89) across similar periods respectively.

Conclusions. In 2024 –2025, B19 infection during pregnancy was associated with a substantially increased risk of fetal complications. Relative risk was nearly fourfold higher than pre-pandemic levels, suggesting a stronger observed association between B19 infection and adverse pregnancy outcomes in the post-pandemic period. Although absolute complication risk remains low, clinicians should remain vigilant and closely monitor pregnant women with confirmed or suspected B19 infection.