Maternal and neonatal outcomes after infection with monkeypox virus clade I during pregnancy in DR Congo: a pooled, prospective cohort study

BACKGROUND: Monkeypox virus (MPXV) has been linked to vertical transmission, but systematic data are scarce. We aimed to describe the sociodemographic, clinical, and virological characteristics and assess the frequency and determinants of adverse outcomes in pregnant women with MPXV clade I infection. METHODS: In this prospective cohort study, we pooled data from three cohort studies (MBOTE-SK, PREGMPOX, and Uvira mpox) and one randomised controlled trial (PALM007) conducted in the South Kivu, Maniema, and Sankuru provinces of DR Congo between Dec 29, 2022, and June 20, 2025. Pregnant women and adolescent girls with a PCR-confirmed diagnosis of mpox were followed up throughout hospitalisation for mpox, delivery, and until discharge during the postpartum period. We extracted data on sociodemographic characteristics, MPXV exposure, clinical and obstetric presentation, and laboratory results. In a univariable analysis, we examined factors associated with the following adverse outcomes: spontaneous or missed abortion (<20 weeks of gestation), stillbirth (≥20 weeks of gestation), preterm birth (<37 weeks of gestation), live birth of a neonate with macroscopic mpox-like lesions, early (first 7 days) neonatal death, congenital anomaly, or maternal death (during pregnancy or discharge postpartum). FINDINGS: We collected data from 89 pregnant women in the first (25 [28%]), second (31 [35%]), and third (33 [37%]) trimesters across all four studies: MBOTE-SK (36 [40%]), PREGMPOX (24 [27%]), PALM007 (25 [28%]), and Uvira mpox (four [4%]). All participants recovered from mpox; no maternal deaths were reported. During hospitalisation for mpox, fetal loss was reported in 17 (19%) women. Final pregnancy outcomes were known for 69 (78%) participants; adverse outcomes were reported in 35 (51%) women (95% CI 38-63), including fetal loss in 31 (45%; 95% CI 33-57; 16 [52%] spontaneous abortions, four [13%] missed abortions, and 11 [35%] stillbirths). Of the 38 live births, four neonates had congenital mpox-like lesions; one infant died a few hours after birth. No preterm births or congenital abnormalities were recorded. MPXV infection during the first trimester was associated with a higher risk of adverse pregnancy outcomes than during the second (risk ratio [RR] 0·6 [95% CI 0·4-0·9]) and third (0·2 [0·1-0·4]) trimesters (p=0·0008). Adverse outcomes were also associated with high viral load in skin lesions (PCR cycle threshold ≤30; RR 3·5 [95% CI 1·0-12·3]; p=0·045), direct sexual contact with the index case (1·6 [1·1-2·4]; p=0·026), positive HIV status (2·0 [1·4-2·9]; p=0·0002), and the presence of genital lesions (1·9 [1·1-3·2]; p=0·025). INTERPRETATION: MPXV clade I infection in pregnancy is associated with a high risk of fetal loss and congenital infection, particularly during the first trimester. Targeted preventive and clinical strategies are urgently needed to protect pregnant women and their infants in settings that are endemic and epidemic for mpox. FUNDING: The European and Developing Countries Clinical Trials Partnership, the Belgian Directorate-General Development Cooperation and Humanitarian Aid, the Swiss National Science Foundation, the Research Foundation-Flanders, the Gates Foundation, the Intramural Research Program of the National Institutes of Health, and the National Cancer Institute.