Over the course of the pregnancy, the mother's immunity is tweaked to support the pregnancy. However, it can also lead to preterm births.
Scientists have conducted many studies to find out what actually causes preterm birth in humans. A recent set of studies may indicate a role of maternal immunity in the early arrival of the baby. However, it also indicates something grave – it also plays a role in miscarriages.
Immunity is the gift every living being has that keeps it that way – alive and kicking. The role of immunity in the human body is simple – find out what does not belong inside the body and get rid of it. And that is why the immune cells of the body attack bacteria and try to attack viruses.
That said, it is a different thing when it comes to a baby. Technically, it is a foreign object. And so, many scientists and researchers thought till now that the mother’s immunity is in a state of suppression throughout the pregnancy. However, newer research suggests that immunity is far from suppressed in pregnancy. In fact, it plays an active role in implantation, maintenance of the pregnancy, and even labour!
Immunity and pregnancy
A recently published study proposes a theory – an immune clock of the human pregnancy. According to the researchers from the Stanford University, USA, and Ghent University, Belgium, the immunity starts from a state of pro-inflammation in the early days of pregnancy, followed by a state of anti-inflammation, followed by a state of pro-inflammation, leading to labour.
For the implantation to occur, the immune cells of the mother have to prime the uterus. A few cells ‘invade’ the lining of the uterus and cause inflammation there. Implantation cannot occur without a primed uterus, and so, the immunity has to be in a pro-inflammation phase at that time. It remains in that phase throughout the first trimester.
During the second trimester, the foetus grows rapidly. As the cells also contain genes derived from the father, they may express as antigens on the surface. This may lead to the immune cells attacking the growing foetus. So, a type of immune cells, Regulatory T cells (Tregs) prevent such attacks, marking the anti-inflammation phase.
In fact, when the Treg cells are found in low numbers, miscarriages occur as the mother’s immune cells end up attacking the growing foetus.
Near the term, the immunity switches back to a pro-inflammation phase. In fact, if it does not go in this phase, the mother will not go into labour. When there is an abnormality in this immune response, there are chances of preterm labour.
Infections and preterm labour
In addition to the body’s own immune clock, there are certain infections that may lead to preterm labour. The mother’s body is capable of fighting off most of the infections. However, intrauterine infections can lead to preterm labour. The viruses
Studies indicate that 2 in 5 preterm deliveries have some sort of an association with an infection. Many times, cervical insufficiency is also indicated in an increased incidence of intrauterine infections. However, there is a theory about viruses in particular.
Dr Gil Mor is a scientist at the Department of Reproductive Sciences, University of Yale, USA. His team believes that pregnancy complications such as pre-term delivery may result from polymicrobial infections. They have recently shown that viral infection during pregnancy can lead to fetal inflammation and sensitisation to bacterial products. This is again, driven by maternal immunity.
This new research is important as this changes the way doctors will look at immunity especially during the pregnancy. And as markers of immunity can be detected in blood, scientists might develop some simple blood tests to detect the risk of miscarriages or preterm labour.