In a prospective cohort study investigators will examine characteristics and clinical outcomes of treatment with ART in women with tubal factor infertility (TFI) with regard to seropositivity to antichlamydial antibodies.

At the first day of stimulation blood analyses for immunoglobulin G (IgG), immunoglobulin A (IgA) and immunoglobulin M (IgM) to major chlamydial antigens (anti-C.trachomatis), major outer membrane protein (MOMP) and plasmid-encoded protein (pgp3) will be performed for patients found eligible for the study. According to the result of chlamydial antibody test (CAT) participants will be divided into two groups: group A - women with at least one of antibodies detected (CAT+); Group B - seronegative subjects (CAT-). Women of both groups will undergo a conventional ovarian stimulation (COS) with GnRH antagonist and daily gonadotropin administration at the dose of 150-300 international unit (IU). Retrieved oocytes following fertilization (conventional IVF or ICSI) will be cultured to Day 3-5 in vitro; ultrasound guided single or double embryo transfer will be performed; remaining embryos of eligible quality will be vitrified. Patients will be followed up to live birth. Frozen/thawed embryo transfers (FET) will be performed until at least one live birth (≥20 weeks of gestation) occurred or all embryos resulting from the mentioned assisted ovarian stimulation were used.