Mothers retain cells from their babies in their bodies after pregnancy, scientists have found, in a discovery which may help explain why some couples can conceive naturally after IVF.
US experts found that foetal cells were scattered throughout a mother’s body after birth, lingering in areas such as the heart, womb and tissues.
Experts believe that traces of a baby remain in its mother as a form of ‘vaccination’ which helps her body welcome a future pregnancy by the same father.
“Very small numbers of foetal cells can be found in the heart, liver, intestine, uterus and other tissues,” said Dr Sing Sing Way, of Cincinnati Children’s Hospital and the Centre for Inflammation and Tolerance.
“The cells are absolutely there in humans. The fact that we are made up of more than just cells with our own genetics, but also cells from our mothers and our children, is a fascinating idea.
“While we did not study IVF specifically, the biology we study should apply to both natural and IVF, as long as it’s a healthy, uncomplicated pregnancy.”
Pregnant naturally after IVF
In June 2023, University College London found that one in five women become pregnant naturally after having a baby through IVF, suggesting fertility techniques may actually boost natural conception.
Dr Way said that a first pregnancy allows babies to encounter a “hospitable niche” which triggers greater “hospitality” in their mother for future siblings.
In 2012, the Cincinnati team discovered that a first pregnancy makes a woman’s body much less likely to reject a second pregnancy with the same father.
At the time they found that mothers carry a long-term supply of immune-suppressive T cells which specifically recognise a foetus created by the same couple.
During pregnancy the T cells instruct the rest of the immune system to stand down and let the pregnancy develop.
In the new study, the scientists discovered that the T cells keep flourishing even after birth because they are receiving signals from tiny populations of baby cells that remain in mothers after pregnancy.
Although the T cell signalling work was carried out in animal studies, the team confirmed that the same baby cells were found throughout a human mother’s body and said they shared the same cellular “crosstalk”.
It is already known that children maintain a small supply of cells transferred from their mothers during pregnancy which helps explain why an organ transplant from a mother is likely to be successful compared with a donor organ from their father.
Explain multiple miscarriages
But while daughters “forget” the cells from their mothers when they become pregnant themselves, the new research shows the child cells remain in the mother.
Scientists say the study may also give clues as to why some couples may have multiple miscarriages or other pregnancy complications because the woman’s immune system can remember bad pregnancy outcomes as good outcomes.
“By investigating how prior pregnancy changes the outcomes of future pregnancies – or in other words how mothers remember their babies – our findings add a new dimension to our understanding of how pregnancy works,” added Dr Way.
“If we can learn ways to mimic these strategies, we may be better able to prevent complications in high-risk pregnancies.
“The challenge will be to identify specifically what a mother’s immune system retains from a pregnancy with a poor outcome.
“If we can isolate how those mechanisms differ from a healthy outcome then we would have a target for developing treatments to improve outcomes in high-risk pregnancies,” he said.
The research was published in the journal Science.