Bone marrow vital for pregnancy

Awoman’s bone marrow may determine her ability to start and sustain a pregnancy, according to new research. The study shows that when an egg is fertilised, stem cells leave the bone marrow and travel via the bloodstream to the uterus, where they help transform the uterine lining for implantation. If the lining fails to go through this essential transformation, the embryo cannot implant, and the body terminates the pregnancy.

“We have always known that two kind of things were necessary for pregnancy,” says senior author Hugh Taylor, a professor of obstetrics, gynecology, and reproductive sciences at Yale University. “You must have ovaries to make eggs, and you must also have a uterus to receive the embryo. But knowing that bone marrow has a significant role is a paradigm shift.”

Previous research has indicated that, in small numbers, bone marrow-derived stem cells contribute to the nonimmune environment of the non-pregnant uterus, but it’s remained unknown if and how stem cells affect a pregnant uterus. In this study, the researchers were able to prove the physiological relevance of stem cells to pregnancy.

“Some of these bone marrow-derived mesenchymal stem cells travel to the uterus and become decidual cells, which are the cells that are essential for the process of implantation and pregnancy maintenance,” explains first author Reshef Tal, assistant professor of obstetrics, gynecology, and reproductive sciences.

In two mouse models with the Hoxa11 gene defect, which presents in mice as a defective endometrium, the researchers found that a bone marrow transplant from a healthy donor could improve fertility by promoting sufficient decidualization of the endometrium.

In mice with only one copy of the defective gene, the transplant saved pregnancies that would otherwise have been lost and increased litter sizes, while in the mice with two bad copies of the gene, which were thus entirely infertile, the transplant caused growth and repair of the defective endometria.