Implantation in the lower half of the uterine cavity and decreased trophoblastic thickness can predict miscarriage: a prospective cohort study.

Embryo implantation is vital for successful conception but remains to be fully understood. Trophoblast invasion is key for implantation, with anchorage and depth of placentation determined by its extent. There is a dearth of synchronous information regarding in vitro fertilisation (IVF), implantation site and trophoblastic thickness (TT). Our aim was to determine whether pregnancy implantation site and TT, had an impact on outcomes of IVF pregnancies. This prospective observational study was undertaken at a tertiary referral UK fertility unit over 14-months, collecting data on implantation site and TT from three-dimensional (3D) images of the uterus following early pregnancy scan. Of the 300 women recruited, 277 (92%) had live births, 20 (7%) miscarried, 2 (0.7%) had stillbirths and one (0.3%) had a termination. Significantly more pregnancies that resulted in miscarriage 7/20 (35%) were located in the lower uterine cavity when compared to ongoing pregnancies 15/277 (5%) (p<0.01). TT was significantly higher in ongoing pregnancies when compared with those who miscarried (7.2mm vs 5.5mm; p<0.01). Implantation in the lower half of the uterine cavity and decreased TT are significantly associated with an increased rate of miscarriage. Identification of those at risk should prompt increased monitoring with the aim of supporting these pregnancies.