A prospective cohort study from the Democratic Republic of the Congo (DRC) suggests that mpox infection during pregnancy, particularly in the first trimester, is associated with a high risk of fetal loss.
The study, published late last week in The Lancet, pooled data from four studies conducted between December 2022 and June 2025 in one DRC region where mpox clade 1b is in circulation and two regions in which mpox clade 1a is endemic.
Researchers followed 89 pregnant women with polymerase chain reaction (PCR)-confirmed mpox who were hospitalized for mpox during their pregnancy. Among the 69 participants with known pregnancy outcomes, 51% experienced an adverse outcome at one point in pregnancy.
Nearly half (45%) of the pregnancies ended in fetal loss, including spontaneous abortion (52%), missed abortion (13%), and stillbirth (35%). Of the 38 live births, four infants had congenital mpox-like skin lesions, and one of them died within hours of birth. No maternal deaths or preterm births were reported.
Adverse outcomes in 94% of pregnancies during first trimester
Adverse outcomes were more frequent when mpox infection occurred during the first trimester. Adverse outcomes occurred in 94% of pregnancies during the first trimester, compared with 59% in the second trimester (risk ratio [RR], 0.6) and 17% in the third (RR, 0.2).
In a commentary accompanying the study, Akaninyene Eseme Ubom, MBBS, MSc, and Sebastine Oseghae Oiwoh, MBBS, note that pregnancy itself may increase vulnerability to severe outcomes.
“Pregnant women are at high risk of severe mpox due to the immunological and hormonal changes that occur in pregnancy,” they write, adding that evidence indicates that mpox clade 1 is associated with more significant adverse pregnancy outcomes and vertical transmission (crossing the placenta from mother to fetus) than clade 2.
Several other factors were linked to adverse pregnancy outcomes, including high viral load in skin lesions (RR, 3.5), genital lesions (RR, 1.9), sexual contact with someone with a suspected case of mpox (RR, 1.6), and HIV infection (RR, 2.0).
Observed rates of fetal loss in the current study exceed general pregnancy-loss risk estimates for the region and resemble historical data on pregnancy outcomes associated with other viruses. “Therefore, vertical transmission and adverse pregnancy outcomes seem to be a key characteristic of orthopoxvirus infections,” Ubom and Oiwoh write.
The findings build on earlier reports that suggested mpox can cross the placenta and that mpox-related complications are not uncommon. Because the current study pooled data from multiple cohorts, it provides some of the most comprehensive evidence to date on pregnancy outcomes associated with mpox clade 1, write the authors.
Study limitations include missing information, loss to follow-up after hospitalization, and differences across study sites.
The study authors conclude that mpox acquired during pregnancy calls for targeted prevention strategies, including prioritization of pregnant women for vaccination with non-replicating vaccines and expanded research on antiviral therapies that can be safely used during pregnancy.
Mpox “ acquired during pregnancy should be regarded as a congenital pathogen, with outcomes resembling those of other congenital viral infections,” they write. “Long-term studies are needed to assess the developmental consequences of congenital mpox."
