Ectopic pregnancy in uterosacral ligament following in vitro fertilisation (IVF) in a patient with Allen-Masters syndrome.

We describe the case of a woman with mild endometriosis and Allen-Masters syndrome after in vitro fertilisation (IVF), presenting at 7 weeks 2 days gestation with abdominal pain. A transvaginal ultrasound revealed a gestational sac with a non-viable fetus near the right ovary. Laparoscopy was performed due to escalating abdominal pain which revealed a ruptured ectopic pregnancy at the right uterosacral ligament (USL) and blood in the pouch of Douglas. A peritoneal incision along the USL facilitated drainage and removal of the ectopic pregnancy. A pathological investigation described the presence of endometrial tissue directly adjacent to products of conception, which suggested a retroperitoneal implantation that may have been facilitated by the presence of an endometriotic lesion. This case underscores the distinctive clinical trajectory of unconventional ectopic pregnancies, provides novel insights into the pathophysiological mechanism of ectopic implantation and underscores the crucial role of comprehensive patient assessment during IVF and subsequent pregnancy in ensuring effective management.