When a pregnant woman contracts the flu, it can have devastating effects on the fetus, due to the immune response being too strong. A great step forward for possible treatments.
- The flu has a much harsher effect on pregnant women and can also disrupt the growth of the fetus or even cause miscarriage.
- According to a pre-clinical study, the flu transforms an underlying inflammation – caused by pregnancy – into generalized inflammation.
- Under severe strain, the immune response crushes the blood vessels which circulate blood less well, especially to the baby.
Why a “simple” flu can create life-threatening complications for the fetus during pregnancy? An Australian pre-clinical study from RMIT University, in collaboration with Irish researchers, published on September 21 in the journal Proceedings of the National Academy of Sciences (PNAS), advances new explanations. “Conventional thinking has blamed the weakened immune system that occurs during pregnancy, but what we are seeing is the opposite effect — influenza infection leads to a dramatically heightened immune response”explains Dr. Stella Liong, lead author of the study. The inflammation we found in the circulatory system is so overwhelming, it’s like a vascular storm wreaking havoc throughout the body.”
Pregnant women who get the flu are at higher risk of hospitalization for pneumonia and other complications. In case of flu, the fetus has an increased risk of fetal growth retardation and premature birth, while the expectant mother is more prone to miscarriages. However, the flu is not transmitted directly from mother to child.
Dysfunction of blood vessels
In a previous study on influenza A, researchers had observed that the virus behaved differently in the bodies of pregnant and non-pregnant mice. In non-pregnant mice, the influenza infection remains in the lungs, while in pregnant subjects, the virus spreads through the circulatory system through blood vessels. The infection leads to inflammation of the blood vessels, thus affecting their functions, deteriorating the health of the mother, and, ultimately, the growth of the fetus fueled by this blood flow. In this study, the researchers found that pregnant mice with influenza had severe inflammation of large blood vessels and the aorta, the main artery supplying blood to the heart. At the level of the blood vessels, they observed that they only functioned at 20-30% of their capacity, against 90 to 100% in normal times.
“We know that flu infection during pregnancy increases the risk of babies being smaller and suffering from lack of oxygen, says Stavros Selemidis, a professor at RMIT and lead author of the study. Our research shows the critical role the vascular system could play in this: inflammation of blood vessels reduces blood flow and the transfer of nutrients from mother to baby.” Although the researchers did not measure blood flow directly, they did note an increase in biomarkers of oxygen deprivation in the fetuses of mice infected with influenza.
Pregnancy, a special condition
How to explain that this phenomenon only occurs during gestation? For the researchers, the explanation would come from the fact that the mother is in a state of constant underlying inflammation during her pregnancy, causing the placenta to secrete proteins and release fetal DNA into her blood. According to them, influenza infection could flip the underlying inflammation into a systemic inflammatory event.
This mechanism could be related to the preeclampsia, a dangerous pregnancy complication characterized by high blood pressure. “We found that the same protein that is elevated in preeclampsia is also significantly elevated with influenzahe assures. Although further research is needed to uncover this link, it could mean that drugs targeting vascular inflammation that are currently being tested could potentially be repurposed for influenza infection in pregnancy in the future.” Pending these advances, the flu vaccine is strongly recommended for pregnant women.
.
