Mpox and pregnancy: a risk for the fetus?

By Ana Espino | Published on March 12, 2026 | 3 min read


Mpox (formerly known as monkeypox) is a viral zoonosis caused by the Monkeypox virus (MPXV), a double-stranded DNA orthopoxvirus. Initially endemic in Central and West Africa, the virus experienced a major global expansion between 2022 and 2024, prompting the World Health Organization (WHO) to declare a public health emergency. More than 80,000 cases have been reported in over 100 countries.   Although most infections are mild, certain populations are at higher risk of severe disease, including pregnant women.

Obstetric complications such as miscarriage, intrauterine fetal death, and prematurity have been reported. Available evidence also suggests the possibility of transplacental vertical transmission, raising questions about the underlying pathophysiological mechanisms.  

However, clinical data remain limited, heterogeneous, and often derived from low-resource settings. The objective of this review, published in the Journal of Medical Virology in 2025, is to synthesize the available evidence on MPXV infection during pregnancy, with a particular focus on maternal–fetal transmission and its clinical implications.  

Can the virus cross the placental barrier?  

This narrative review analyzes clinical, epidemiological, and experimental data concerning Mpox infection in pregnant women. Historical data mainly originate from African cohorts infected with clade I, the more virulent lineage. In a study conducted in the Democratic Republic of the Congo (2007–2011), three out of four infected pregnant women experienced adverse fetal outcomes, including intrauterine fetal death. One documented case of congenital Mpox syndrome included diffuse skin lesions, fetal hydrops, and hepatomegaly. The virus was detected by PCR in amniotic fluid, fetal blood, and placental tissue, confirming vertical transmission.  

In contrast, during the global outbreak of 2022–2023 associated with clade IIb, more than 50 cases of infection in pregnant women were reported without maternal deaths or major documented fetal complications. Overall lethality was below 0.1%, suggesting lower virulence. Inter-clade differences may be explained by mutations affecting viral entry proteins such as B22R, as well as a reduced capacity for cellular dissemination.  

Animal models further support the hypothesis of in utero transmission. In rhesus macaques, infection with clade IIb resulted in fetal deaths and viral detection in placental villi. In vitro analyses showed that extravillous trophoblasts are permissive to infection, allowing viral replication and release of viral particles through filopodial extensions. From an immunological perspective, placental infection triggers a marked inflammatory response, characterized by macrophage activation and increased production of pro-inflammatory cytokines. However, the precise mechanisms by which the virus crosses the fetoplacental barrier remain poorly understood.  

Regarding clinical management, tecovirimat represents the main antiviral option, with no evidence of teratogenicity in animal studies. However, no robust clinical data currently demonstrate its effectiveness in preventing vertical transmission.  

Monitoring, understanding, and anticipating  

Mpox infection during pregnancy represents a potentially high-risk situation, particularly with the more virulent viral clades. This review aimed to assess the evidence for vertical transmission and associated obstetric outcomes. Available data confirm that clade I is associated with severe fetal complications, including intrauterine death and congenital infection.

By contrast, clade IIb, responsible for the recent global outbreak, appears to be associated with lower obstetric morbidity. The main limitations include the small size of available cohorts, the lack of systematic follow-up of infected pregnancies, and the absence of standardized analyses of placental and fetal tissues.  

Prospective multicenter studies incorporating placental analyses, viral load assessment, and neonatal follow-up are essential to clarify the true level of risk. A better understanding of placental tropism and inter-clade differences will help optimize obstetric monitoring and guide therapeutic strategies for pregnant women exposed to MPXV.

Read next: West Nile: the fever is rising!

About the author – Ana Espino
PhD in Immunology, specialized in Virology  
As a scientific writer, Ana is passionate about bridging the gap between research and real-world impact. With expertise in immunology, virology, oncology, and clinical studies, she makes complex science clear and accessible. Her mission: to accelerate knowledge sharing and empower evidence-based decisions through impactful communication.