Definition: Lutelet is a type of muscle in humans that helps to support and maintain pregnancy. It consists of two main groups, the luteal cell group (LCG) and the oocyte-specific group (OSG). The LCG, also known as the placental lactifer, contains specialized cells that help to produce hormones during pregnancy. These hormones include progesterone and luteinizing hormone, which are essential for the development of the fetus.