Uterine Factors Modify the Association Between Embryo Transfer Depth and Clinical Pregnancy: A Retrospective Study in 7849 Fresh Transfer In Vitro Fertilization Cycles

Abstract

The embryo position is supposed to affect implantation following embryo transfer. However, embryo dislodging caused by uterine contraction may occurred after transfer. The retrospective study was to investigated whether the factors associated with uterine contractility, such as endometrial thickness and progesterone elevation, affect the association between embryo position and implantation. A total of 7849 fresh transfer cycles on conventional stimulation in a single IVF centre during the period 2013–2015 was reviewed. Patients were categorized according to quartiles of embryo-fundus distance (≤9, 9.1-11, 11.1-14, ≥1.4 mm, respectively). Adjusted for confounding factors, the odds ratio (OR) (95%CI) for clinical pregnancy was 0.90 (0.79-1.02), 0.86 (0.74-0.99) and 0.70 (0.60-0.82) respectively in quartiles 2 through 4, comparing with quartile 1. However, ORs were significantly increased when endometrial thickness was < 8 mm. The ORs comparing quartiles 2 through 4 with quartile 1 increased 1.96 (95%: 1.33-2.90), 1.20 (95%: 0.78-1.87) and 1.98 (95%: 1.20-3.26) fold respectively in cycles with an endometrial thickness < 8 mm than in cycles with a normal endometrial thickness (8-11 mm). Elevated progesterone on the day of hCG and blastocyst stage transfer reduced the ORs. Our data suggested an interaction between patient characteristics and embryo transfer techniques.