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 EspinoPhD 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.
