Bioengineering Studies of the Embryo Transfer Procedure

Embryo transfer success: It is in our hands

Embryo transfer (ET) is considered as a critical step in the process of in vitro fertilization. Interestingly, studies have consistently shown significant outcome differences between physicians. Although the outcome of ET is not related to the physician's experience and specifically not different between fellows and attending physicians, certain techniques have been found to affect the success rate. This review summarizes the existing evidence regarding the impact of the individual physician performing ET and the techniques used.

Embryo location in the uterus during embryo transfer: An in vitro simulation

OBJECTIVE

To evaluate the location of transferred embryos under various parameters during embryo transfer in in vitro fertilization (IVF) by applying an in vitro experimental model for embryo transfer (ET).

METHODS

Mock ET simulations were conducted with a laboratory model of the uterine cavity. The transfer catheter was loaded with a sequence of air and liquid volumes, including development-arrested embryos donated by patients. The transfer procedure was recorded using a digital video camera. An orthogonal design, including three independent variables (uterine orientation, distance of the catheter tip to the fundus, and injection speed) and one dependent variable (final embryo position), was applied.

RESULTS

The uterine cavity was divided into six regions. The distribution of the transferred matter within the uterine cavity varied according to the uterine orientation. Medium speed-injected embryos were mostly found in the static region while fast- and slow-speed injected embryos were mostly found in the fundal region and the cervical-left region, respectively. The possibility of embryo separation from the air bubble increased from 11.1% in slow injection cases to 29.6% and 48.1% in medium and fast injection cases, respectively.

CONCLUSION

The experimental model provides a new method for investigating ET procedures. Fast injection of embryos into a retroverted uterus may be more likely to result in embryo separation from the air bubble.

Biomechanics of the human uterus

The appropriate biomechanical function of the uterus is required for the execution of human reproduction. These functions range from aiding the transport of the embryo to the implantation site, to remodeling its tissue walls to host the placenta, to protecting the fetus during gestation, to contracting forcefully for a safe parturition and postpartum, to remodeling back to its nonpregnant condition to renew the cycle of menstruation. To serve these remarkably diverse functions, the uterus is optimally geared with evolving and contractile muscle and tissue layers that are cued by chemical, hormonal, electrical, and mechanical signals. The relationship between these highly active biological signaling mechanisms and uterine biomechanical function is not completely understood for normal reproductive processes and pathological conditions such as adenomyosis, endometriosis, infertility and preterm labor. Animal studies have illuminated the rich structural function of the uterus, particularly in pregnancy. In humans, medical imaging techniques in ultrasound and magnetic resonance have been combined with computational engineering techniques to characterize the uterus in vivo, and advanced experimental techniques have explored uterine function using ex vivo tissue samples. The collective evidence presented in this review gives an overall perspective on uterine biomechanics related to both its nonpregnant and pregnant function, highlighting open research topics in the field. Additionally, uterine disease and infertility are discussed in the context of tissue injury and repair processes and the role of computational modeling in uncovering etiologies of disease. WIREs Syst Biol Med 2017, 9:e1388. doi: 10.1002/wsbm.1388 For further resources related to this article, please visit the WIREs website.

Mathematical modeling of the female reproductive system: from oocyte to delivery

From ovulation to delivery, and through the menstrual cycle, the female reproductive system undergoes many dynamic changes to provide an optimal environment for the embryo to implant, and to develop successfully. It is difficult ethically and practically to observe the system over the timescales involved in growth and development (often hours to days). Even in carefully monitored conditions clinicians and biologists can only see snapshots of the development process. Mathematical models are emerging as a key means to supplement our knowledge of the reproductive process, and to tease apart complexity in the reproductive system. These models have been used successfully to test existing hypotheses regarding the mechanisms of female infertility and pathological fetal development, and also to provide new experimentally testable hypotheses regarding the process of development. This new knowledge has allowed for improvements in assisted reproductive technologies and is moving toward translation to clinical practice via multiscale assessments of the dynamics of ovulation, development in pregnancy, and the timing and mechanics of delivery. WIREs Syst Biol Med 2017, 9:e1353. doi: 10.1002/wsbm.1353 For further resources related to this article, please visit the WIREs website.

Modeling Embryo Transfer into a Closed Uterine Cavity

Embryo transfer (ET) is the last manual intervention after extracorporeal fertilization. After the ET procedure is completed, the embryos are conveyed in the uterus for another two to four days due to spontaneous uterine peristalsis until the window time for implantation. The role of intrauterine fluid flow patterns in transporting the embryos to their implantation site during and after ET was simulated by injection of a liquid bolus into a two-dimensional liquid-filled channel with a closed fundal end via a liquid-filled catheter inserted in the channel. Numerical experiments revealed that the intrauterine fluid field and the embryos transport pattern were strongly affected by the closed fundal end. The embryos re-circulated in small loops around the vicinity where they were deposited from the catheter. The transport pattern was controlled by the uterine peristalsis factors, such as amplitude and frequency of the uterine walls motility, as well as the synchronization between the onset of catheter discharge and uterine peristalsis. The outcome of ET was also dependent on operating parameters such as placement of the catheter tip within the uterine cavity and the delivery speed of the catheter load. In conclusion, this modeling study highlighted important parameters that should be considered during ET procedures in order to increase the potential for pregnancy success.