Hormonal changes during pregnancy have an effect on the mother's immune system, which leads to an increased susceptibility to listeriosis in the mother. According to the American Centre for Disease Control, pregnant women are about 20 times more likely than other healthy adults to get listeriosis. In fact, about one-third of listeriosis cases result during pregnancy. Listeriosis can be transmitted to the foetus through the placenta even if the mother is not showing signs of illness. This can lead to premature delivery, miscarriage, stillbirth, or serious health problems for her newborn.