Introduction
In vitro fertilization and embryo transfer (IVF-ET) is a globally
utilized form of assisted reproductive technology, and ET is the final
and most essential step thereof 1. During the ET
process, the fertilized embryos are cultured in vitro and placed
directly inside the uterine lumen via an ET catheter2. Previous studies investigating the main factors
affecting the implantation rate reported endometrial receptivity and
embryo quality as risk factors 3. However, ET, as the
last and probably most underestimated step, has not been developed as
much as the other aspects of the IVF process. Studies have shown that
transferred embryos do not always implant in situ, despite the transfer
process being performed under ultrasound guidance 4,
5. The catheter loading, catheter position, injection speed, uterine
peristalsis and patients’ posture during ET may affect the migration of
embryos 4, 6, 7. Poindexter et al. reported that
approximately 15% of the transferred embryos were expelled from the
uterine cavity and were found in the cervical os, fallopian tubes, or
the ET catheter 8. Baba demonstrated that
approximately 80% of embryos implant in areas to which they initially
are transferred and approximately 20% implant in other areas9. The migration of the transferred embryos might make
detrimental effect on a successful pregnancy, and also predisposes the
patient to ectopic pregnancy 10.
A laboratory simulation of ET into a uterine model demonstrated that the
dispersion of the transferred matter depend on the position of sagittal
cross-section of the uterine cavity with respect to the horizon6. However, the in vitro model can not represent the
real situation in vivo, and the cleavage stage embryos and blastocysts
might be affected differently by the inclination of uterus due to their
different migration duration before implantation. Therefore, it remains
unclear whether the inclination of uterine corpus affects the pregnancy
outcomes of IVF-ET.
This study investigated whether the inclination of the uterine corpus
affect the pregnancy outcomes in IVF-ET, and whether different uterine
inclination affect the pregnancy outcomes of embryos at different
developmental stages.