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Life threatening swine flu illness associated with pregnancy

Pregnancy may increase the risk for critical illness related to swine flu (H1N1 influenza), according to the results of a population-based cohort study reported in the March 18, 2010 online edition of the British Medical Journal.

"Pregnant women are at increased risk of influenza and its complications," write the authors Ian Seppelt and colleagues from the Australian and New Zealand Intensive Care Influenza Investigators, in collaboration with the Australasian Maternity Outcomes Surveillance System. "Information is, however, limited on medical and obstetric management and maternal and infant outcomes when pregnancy is complicated by 2009 H1N1 related critical illness”

The report describes the characteristics, obstetric and intensive care management, and birth outcomes of all pregnant and recently pregnant women with confirmed swine flu infection admitted to Australian and New Zealand intensive care units during the winter of 2009.

The primary study endpoints were maternal and neonatal mortality and morbidity. Of 209 women of child-bearing age (aged 15 - 44 years) who were admitted to an intensive care unit in Australia or New Zealand with confirmed 2009 H1N1 influenza between June 1 and August 31, 2009, almost a third (30.6%) were either pregnant or had recently given birth.

Risk of serious disease increased 13-fold

Risk for admission to an intensive care unit was markedly increased in pregnant or postpartum women with 2009 H1N1 influenza compared to non-pregnant women of childbearing age. The relative risk (RR) was found to be 7.4. In other words, a pregnant or newly delivered woman was more than 7 times more likely to have serious disease requiring intensive care admission compared to a non-pregnant counterpart. For women in the later stages of pregnancy; those at 20 or more weeks' gestation; the increase in risk was even more pronounced at 13-fold (RR, 13.2; 95% CI, 9.6 - 18.3).

Twenty-two women (34%) were postpartum and 2 had miscarried when they were admitted to an intensive care unit; 14 (22%) delivered during their stay in intensive care, and 26 (41%) were still pregnant when discharged from an intensive care unit and subsequently delivered.

Maternal deaths and stillbirths

Of 44 women (69%) who were mechanically ventilated, 9 (14%) received extracorporeal membrane oxygenation. There were 7 maternal deaths (11%). Of 60 births after 20 weeks' gestation, there were 44 stillbirths and 3 infant deaths. Of the live-born babies, 22 (39%) were preterm and 32 (57%) were admitted to a neonatal intensive care unit. Two of 20 babies tested were positive for the 2009 H1N1 virus.

Vaccination (immunisation) for at risk groups

"Pregnancy is a risk factor for critical illness related to 2009 H1N1 influenza, which causes maternal and neonatal morbidity and mortality," the study authors write. "No woman in this cohort had been immunised against seasonal influenza despite established recommendations that pregnant women should be immunised."

Limitations of this study include small sample size and doubtful applicability to other settings.

In an accompanying editorial, Stephen E. Lapinsky, MD, from the University of Toronto in Ontario, Canada, notes that this study offers detailed data regarding maternal risk, as well as maternal and neonatal outcomes.

"Pregnant women, particularly those in the second half of their pregnancy, have a greatly increased risk of developing severe pneumonitis (inflammation of the lungs) associated with pandemic H1N1 (swine flu)," Dr. Lapinsky writes. "Despite evidence of an increase in maternal mortality after infection with H1N1, in the later phases of the pandemic its effect on pregnant women has been less than was initially anticipated.

This may be attributable to worldwide recommendations for pregnant women to be vaccinated against the 2009 H1N1 strain and advice to facilitate early access to antiviral treatment for pregnant women with symptoms of flu."