Maternal and perinatal outcomes in pregnant women with Lassa fever: analysis from the LASCOPE prospective cohort study

Lassa fever, a viral haemorrhagic fever endemic in west Africa, is usually described as associated with severe maternal and perinatal outcomes.

Previous studies reported maternal mortality (whereas overall mortality is about 14% in Nigeria for patients admitted to hospital) and fetal mortality is up to 60%. However, most evidence derives from small case series with substantial limitations.

We aimed to assess maternal death and perinatal outcomes in a prospective cohort study with standardised medical care protocols. We analysed data from the LASCOPE cohort from the Federal Medical Centre Owo, Nigeria, which included all patients with PCR-confirmed Lassa fever.

In this analysis, non-pregnant women of childbearing age (15-45 years) were compared with pregnant women, defined as having an ongoing pregnancy during Lassa fever. The primary maternal outcome was all-cause mortality 28 days after admission and the primary pregnancy outcome was fetal death.

Mortality at 28 days was compared using Kaplan-Meier estimates and a Cox proportional-hazards model, the cumulative incidence of fetal death was estimated with livebirth as a competing event, and the association between gestational age at symptom onset and fetal death was assessed by logistic regression. Between April 4, 2018, and Feb 18, 2023, of 1006 patients in the LASCOPE cohort admitted with PCR-confirmed Lassa fever, 703 were excluded for not being of childbearing age, and 303 were women of childbearing age, of whom 45 were pregnant.

The median age of pregnant women was 28 years (IQR 24-32). The 28-day mortality was comparable between pregnant and non-pregnant women (four [9%; 95% CI 2-21] of 45 vs 19 [7%; 95% CI 4-11] of 258; hazard ratio 1·19 [95% CI 0·41-3·50]; log-rank p=0·75).

Fetal case-fatality rate was 60% (27 of 45), with higher risk of fetal death if infection occurred early in the pregnancy (100% for the first trimester, 82% for the second trimester, and 25% for the third trimester). Each additional week of gestation at symptom onset was associated with a reduction in the odds of fetal death (odds ratio 0·77 [95% CI 0·61-0·90]).

Among 15 liveborn infants, three (20%) died within 30 days.

Although the fetal prognosis was poor, as previously reported, maternal fatality was lower than previously indicated, potentially reflecting improved supportive care and patient monitoring.

These findings suggest that maternal mortality might be lower than historically reported, while confirming the urgent need for specific therapeutic interventions to improve fetal outcomes.