Similar to other previous Flu viruses, the H1N1 virus (previously known as Swine Flu) appears to increase the risk of severe disease and death among pregnant women and new mothers, according to a study published online in the New England Journal of Medicine today.

The study examined 239 women who were hospitalized with H1N1 virus in California between April and August of 2009. Of these women, 94 were pregnant, 8 were postpartum (new mothers) and 137 were not pregnant.

Of the pregnant women and postpartum women, 22% required intensive care, and 8% died. The authors of the study commented that “although an association between severe illness and pregnancy is well documented for seasonal influenza, the rapid clinical deterioration observed in some of our patients appears to be qualitatively different from the course of seasonal influenza observed previously.”

Six women delivered in the ICU (Intensive Care Unit), with four of them requiring an emergency cesarean delivery, which “suggests that the condition of the patients was too unstable at the time of delivery for them to be transferred to an appropriate labor and delivery unit.”

The maternal mortality ratio (the number of mothers who die for every 100,000 live births) for H1N1 virus was 4.3. This high ratio suggests that the virus has the potential to notably increase overall maternal mortality in the United States in 2009.

The Centers for Disease Control and Prevention (CDC) recommend that pregnant women who are thought to have H1N1 should receive prompt antiviral treatment within 48 hours of the first symptoms.

In the study, pregnant women whose treatment was delayed till after 48 hours had four times the risk of admission to the ICU or risk of death than those who received earlier treatment. Delay in treatment is due to the women not promptly seeking medical care, or to health care providers not initiating the treatment on time. It is important to note that in pregnancy, it is often very hard to know whether some symptoms are due to an illness or to the pregnancy itself.

One of the most alarming findings of the study relates to the effectiveness of rapid flu tests (rapid antigen tests) in detecting the virus among patients. These tests are widely available in all hospitals and can be completed within 15 minutes. However, 38% of patients who got these tests received a false negative result, meaning that the test said that they don’t have the virus when they actually had it. This led to delayed treatments and deaths. Among pregnant women, 70% of those who got a false negative result did not get timely antiviral treatment.

The study recommends that pregnant women should be counseled about the importance of getting the H1N1 vaccine, which is safe during pregnancy and provides additional benefits to the newborn infant.