The luteal phase is the last phase of the menstrual cycle. It lasts from ovulation to menstruation, between 12 and 14 days. Thanks to the corpus luteum, the endometrium will thicken to accommodate (implantation). If there is no fertilisation, the (endometrium), under the influence of the (corpus luteum), will disintegrate and a new cycle will begin. This phase is constant =14 days.