A new study has shed fresh light on why some women are infertile and why some pregnancies end in miscarriage, after researchers found that immune cells have an important role to play in both the cases.<br/><br/>An international team has examined the role of a type of immune cells known as macrophages or white blood cells within the ovary, which are found in abundance near developing eggs and in hormone-producing structures within the ovary. The researchers conducted experiments on mice and found that when these cells are depleted there's a significant reduction in the amount of progesterone the ovary produces.<br/><br/>Progesterone is a hormone produced by the ovary which is essential for the maintenance of early pregnancy. <br/>This research identified immune system cells as critical determinants of normal ovarian activity and the<br/>maintenance of early pregnancy. This might be a key to helping prevent early pregnancy loss, such as recurrent miscarriage. The scientists said a number of factors such as smoking, obesity, poor nutrition and stress could all alter the way macrophages behave and may provide reasons for infertility or miscarriage in some women. <br/><br/>