The age of the uterus can regulate successful embryo implantation and pregnancy outcome in mice according to a study in Nature Communications. Previous research has focused on egg defects as a source of age-related complications in pregnancy, but the new findings highlight an underappreciated role for the maternal environment.
Maternal age is known to be a risk factor for reproductive success, and age-related problems with eggs are already known to lead to chromosomal defects within the embryo that can in turn lead to pregnancy loss during the first trimester. Myriam Hemberger and colleagues shed light on the possible causes for pregnancy complications during later stages in pregnancy, such as miscarriage and perinatal death, by studying mice. They notice decreased fetal health and survival as the age of the mother increases in mice. These problems include developmental delays and heart defects, and are associated with defects in the placenta supporting the embryo in the uterus. The authors demonstrate that these problems can be corrected by transferring the embryo from old mothers to young recipients. This indicates that the ability of the uterus to support the placenta and the embryo decreases with age. Ageing of the uterus is associated with reductions in the numbers of immune cells in decidua — structures within the uterus that interact with the placenta to support growth and development of the embryo. The authors also find that cells within the uterus were less responsive to hormones that stimulate decidua formation.
These results highlight how, in mice, the age of the mother may affect embryo survival - not just in terms of age of the egg, but age of the mother’s uterus - to ensure health and survival of an embryo. It should be noted that this is a study in mice and provides no evidence as yet for such a mechanism in humans.