RESUMEN
AIM: To assess whether pain experienced during embryo transfer (ET) is associated with the chance of clinical pregnancy in assisted reproductive technology cycles. METHODS: This was a prospective observational study of 284 women conducted between July 2011 and January 2014. Women under 40 years undergoing in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles followed by fresh/frozen ET were recruited. Pain was measured using a 100-mm visual analogue scale. Several factors relating to both pain and also the nature of the ET procedure were recorded: use of vulsellum, uterine contractility, depth of ET, duration of ET catheter insertion, urgency of micturition, psychological profile tests, salivary α-amylase and salivary cortisol. Primary outcome was the achievement of clinical pregnancy. RESULTS: Women who experienced pain during ET had a significantly lower clinical pregnancy rate compared with women who did not (42.2% vs 53.8%; P = 0.03). Non-pregnant women also had significantly higher pain scores compared with pregnant women (10.3 vs 6.4; P = 0.01). Pain was independent of >20 variables relating to (i) the nature of the ET procedure; (ii) psychological testing; and (iii) potential confounding factors inherent to IVF/ICSI. On binary logistic regression analysis, pain was an independent predictor for the chance of clinical pregnancy (OR, 0.59; 95%CI: 0.37-0.94; P = 0.03). CONCLUSIONS: Pain during ET is independently associated with the chance of clinical pregnancy. The underlying mechanism could involve factors other than nature of the ET and the psychological state of the patient, and warrants further investigation.