Ultrasound and the receptivity of the endometrium.

Ultrasound imaging can be used to assess the endometrium in a number of ways. In particular, time-lapse video recordings can show that the lining of the uterus undergoes rhythmical contractions that vary in strength and intensity throughout the ovarian cycle. These contractions appear to assist in sperm transport at the time of ovulation, but can decrease the chances of a fertilized egg implanting in the uterus if they persist later in the cycle. They are also the cause of ectopic pregnancies occurring in IVF treatment cycles. In order to reduce these uterine contractions and therefore increase the chances of a successful uterine pregnancy, IVF treatment cycles should incorporate minimal stimulation so as to make them as close to natural cycles as possible.