OBJECTIVE:

To evaluate the relationship between the location of the air bubble containing the embryos and the implantation and clinical gestation rates. Secondary: to study the relationship between the position of the cannula tip, the endometrial thickness and the displacement of the bubble with these reproductive outcomes.

MATERIALS AND METHODS:

Retrospective, observational, ultrasound image analysis study of single embryo transfers at blastocyst stage performed by the same specialist at the IVI Foundation, Valencia, Spain, between September 2013 and February 2021. Selection criteria: endometrial thickness ≥ 6 mm at the last ultrasound control, absence of fibroids, BMI less than 30 kg/m2, atraumatic transfers, performed by the same specialist. Based on the location of the air bubble, three study groups were established (high: greater than 0.98 cm, medium: 0.98 to 1.44 cm and low: greater than 1.44 cm) and the odds ratio (OR) and 95%CI were used to evaluate the association between the categories.

RESULTS:

A total of 342 single embryo transfers were studied. The mean age of the patients was 39.70 ± 4.5 years. The relationship between the distance of the air bubble to the uterine fundus and the implantation rate was 61 ± 9% in the high placement group, 64 ± 9% in the medium placement group, and 56 ± 1% in the low placement group (p = 0.437). No differences were observed in the evolutionary gestation rate analyzed by probability of occurrence between groups, with frequencies of 0.60 compared to 0.64 (OR: 1.42; 95%CI: 0.83 to 2.44; p: 0.199) and high to medium location, and frequencies of 0.60 compared to 0.56 (OR: 1.22; 95%CI: 0.72-2.08; p: 0.462) between high and low.

CONCLUSIONS:

No association was found between the air bubble localization and implantation or ongoing pregnancy rates. However, a greater displacement of the bubble was associated with higher ongoing pregnancy rates.