Influence of embryo transfer depth on pregnancy rate: fear the fundus

Abstract

Objective: Though critically important, embryo transfer (ET) is perhaps the least studied step of Assisted Reproductive Technology. A well-designed analysis exploring optimal embryo placement within the uterus is lacking. This we have done investigating the influence of transfer distance from the fundus on clinical pregnancy rate (PR), implantation rate and ectopic PR. Design: Retrospective cohort analysis. Materials/Methods: 699 ultrasound (US)—guided ETs were conducted between January 2000—December 2001 using fresh, frozen, and donor cycles. Mock transfer was performed to measure uterine cavity depth with a Tomcat catheter >1 month prior to treatment. Cavity depth was also measured by abdominal US immediately prior to the transfer, before speculum placement from the vaginal stripe to the fundal endometrium. ET was performed with a Wallace catheter (Cooper Surgical, Shelton CT) using real—time ultrasound and physicians best judgment of cavity depth. Transfer distance from fundus (TDF) was calculated by subtracting the depth of catheter insertion, noted by catheter calibration markings, from the cavity depth, as determined by ultrasound or by mock transfer. i.e. TDFUS = (Cavity Depth US—Depth of Catheter Insertion). Statistical analyses were performed using STATA software incorporating bivariate analysis, ANOVA, and Fishers exact test to build a multivariable logistic regression model to calculate odds ratios and 95% confidence intervals (CI). Results: Overall clinical PR, implantation, and ectopic PR were 37%, 20%, and 6.8%. Cavity Depth US differed from Cavity Depth Mock by at least 10mm in >30% of cases. TDFUS was highly predictive of pregnancy rate. TDF Mock was not predictive of pregnancy. Increasing TDFUS resulted in significantly increased PR as well as lower ectopic rates. See Figure. Using multiple logistic regression, the odds ratio for TDFUS was 1.11 (95% CI: 1.07—1.14). This suggests that for every additional millimeter the embryos are deposited away from the fundus, the odds of clinical pregnancy increased by 11%. Conclusions: After controlling for potential confounders, the clinical PR is significantly influenced by the transfer distance from the fundus. Cavity depth by ultrasound is clinically useful to determine the depth that, beyond which catheter insertion should not occur. Supported by: Baystate Reproductive Medicine.