Transuterine relocation of pregnant uterine horn segment in an exploratory rat model with implications for tubal ectopic pregnancy

Abstract

Ectopic pregnancy affects ~ 2% of pregnancies annually in the United States, with no current treatments allowing for the continuation of the pregnancy. Thus, this study sought to initiate an investigation into the potential design of a surgical technique, in an animal model, that could serve as a foundation for future research into the potential of relocating an ectopic embryo into the uterus at the human level. Female Long-Evans rats were randomly assigned to one of two groups: Embryo Relocation (ER; n = 12; underwent embryo relocation surgery) and Normal Pregnancy (NP; n = 12; carried a normal pregnancy; no surgery). Eight rats/group were allowed to carry their pregnancy to term and deliver, while four had their uteri collected at the end of gestation. Briefly, for the ER group, a uterine horn containing 1-2 embryos was translocated to the contralateral horn, which had been incised and cleared of its contents, prior to being wrapped around the relocated horn. Rat weight, food consumption and vaginal impedance of the mothers were measured throughout the experiment. Ultrasounds were performed and fetal heart rates measured on day 20-21 of gestation. Additionally, rat weight of all offspring was measured at adulthood. Our findings indicate that, in the ER group, 15/15 (100%) of the relocated embryos had detectable heart rates at the end of gestation (within the normal range), 14/15 (93%) were delivered vaginally, and 12/14 (86%) survived until adulthood. A significant decrease in rat weight and food consumption was observed only on the day following surgery. Fertility, as measured by vaginal impedance, was minimally impacted by surgery. Moreover, there was no significant difference between groups in average body weight of offspring at adulthood. Histological analysis indicated a thicker placenta in the ER group, attributable to the fetal part of the placenta, potentially indicating compensatory mechanisms. Our findings reflect a successful transuterine embryo relocation followed by vaginal birth and survival of offspring to adulthood, in a rat model. Such findings lay the foundation for future preclinical research in higher animals, with potential implications on a procedure relevant to human ectopic embryo relocation.

Keywords: Animal model; Ectopic pregnancy; Embryo relocation; Transplant; Tubal.

Fig. 1

Diagram representative of surgical procedure for embryo relocation in a rat model using a bicornuate uterus. (A) Both uterine horns and ovaries were visualized. Green horizontal arrows indicate ovaries and black vertical arrow indicates the corpus and cervix. Bulges in the uterine horns reflect the presence of gestational sacs with maroon crescents indicating placentas. Diagonal lines extending downwards from the uterus reflect mesometrial fat (not included in all images, despite being present in situ). (B) The number of gestational sacs to be relocated was determined and both the uterine horn and mesometrial vessels were ligated superior to the gestational sacs to be relocated (green arrows), as well as inferior to the ovary (not indicated). (C) The ligated portion of the uterine horn (red star) was then excised, preserving the ovary, and the portion of the uterine horn containing the gestational sacs to be relocated was disconnected from as much mesometrial fat as possible (dotted line). The ovary on the original side of the relocated gestational sacs is omitted from future images, but remained in situ. (D) The blood supply from the uterine artery on the cervical side was retained. (E) A longitudinal incision was made along the opposite uterine horn and the contents emptied, creating a “flap”. (F) The gestational sacs to be relocated were rotated so that the placenta(s) were aligned with the mesometrial vessels of the receiving horn. (G & H) Cyanoacrylate surgical glue was used to affix the mesometrial surface of the uterine horn containing the gestational sacs to be relocated to the inner surface of the flap. The flap was brought down and around the gestational sacs and affixed with additional surgical glue to enclose the relocated gestational sacs with the receiving horn. Following the procedure, the cervix remains patent (green arrow).

Fig. 2

Representative images from embryo relocation surgical procedure and follow-up. Images (A-I) are shown with superior (towards the head) aspect at the bottom left corner and inferior (towards the tail) aspect towards the top right corner. (A) Visualization of uterine horns containing gestational sacs (thick black arrows). (B) Insertion of first suture, superior to the gestational sacs (thick green arrows) to be relocated. (C) Ligated portion of the uterine horn to be excised. (D) Excision of the ligated portion of the uterine horn. (E) Removal of mesometrial fat on remaining portion of the uterine horn containing gestational sacs to be relocated. (F) Portion of the uterine horn containing gestational sacs to be relocated prior to relocation to other horn. (G) Creation of the flap in the receiving uterine horn. Inset indicates the flap once created. (H) Gestational sacs being relocated onto flap. (I) Relocated gestational sacs fully enclosed by flap. (J) Rat in the Embryo Relocation group at full-term (D20/D21), prior to tissue collection. Visualization of uterus surrounding the relocated fetus and mesometrial blood vessels. (K) Representative ultrasound image of fetus from full-term rat in Embryo Relocation group, with the head, spine and rib cage labelled.

Fig. 3

Gross anatomical measurements (A & B) and representative images of histological analysis from both Normal Pregnancy (C & D) and Embryo Relocation (E & F) groups. (A) Measurement of fetal width (left) and fetal length (right). (B) Measurement of placental major and minor axes. Green lines represent placental slices for histological investigation. (C & E) Measurement of the specific placental layers at 10x. (D & F) Measurement of basal shoulder, measured from the apex of the labyrinth zone to the furthest point of the basal zone (including giant cells) at 40x. LZ = labyrinth zone, BZ = basal zone, MT = maternal tissue.

Fig. 4

Percentage rat body weight change across gestation in both experimental groups (Embryo Relocation and Normal Pregnancy). Percentage weight change calculated relative to day 1 (D1) of gestation. NP = Normal Pregnancy group, ER = Embryo Relocation group. *** p < 0.001 relative to D7 of gestation (day of surgery) for the ER group.

Fig. 5

Comparison of average vaginal impedance measurements (kΩ) between experimental groups (Embryo Relocation and Normal Pregnancy) pre-breeding and post-weaning. NP = Normal Pregnancy group, ER = Embryo Relocation group; Pre = Pre-breeding impedance, Post = Post-weaning impedance.

Fig. 6

Placental zone thickness across groups as a percentage of total placental thickness. Comparison between Normal Pregnancy and Embryo Relocation groups: *p < 0.05, **p < 0.01, ***p < 0.001. Inset: Placental zone thickness (mm) across groups. LZ = labyrinth zone, BZ = basal zone, MT = maternal tissue; NP = Normal Pregnancy group, ER = Embryo Relocation group.

Fig. 7

Diagram of potential human surgical equivalent. (A) Human female internal genitalia with green arrow indicating an ovary. Black arrow indicates ectopic embryo in fallopian tube. (B) Green lines indicate potential locations of incisions on the fallopian tube, as well as in the uterus. (C) Indicates the rotation of the section of the fallopian tube containing the ectopic embryo. (D) Indicates the uterus sutured closed, with the section of fallopian tube containing the ectopic embryo inside of the uterus. Inset. Represents the ectopic embryo within the uterus.