Uterine contraction has a negative impact on implantation and pregnancy rates. Inhibition of oxytocin receptors decreases uterine contraction frequency both on pregnant and non-pregnant women. Atosiban has been studied as an oxytocin antagonist to decrease uterine contraction frequency in order to increase implantation and pregnancy rates in assisted reproduction. Previous studies have studied 37,5mg total dose which was used both before and during embryo transfer, and found atosiban to be effective in increasing implantation and pregnancy rates. We aim to use a single dose of 6,75mg atosiban before embryo transfer, in order to decrease the dose and cost and possibly introduce a simpler protocol. Our study will also be the first randomized clinical study which investigates the effect of atosiban on frozen-thawed embryo transfer cycles.

Inhibition of uterine contractions in order to increase implantation rates have been studied on several agents in the last two decades. Beta-adrenergic agonists and non-steroidal anti-inflammatory drugs have been shown to have no benefit on implantation rates. Vasopressin V1a and oxytocin receptor antagonist atosiban was first studied on premature labor patients and found to be effective.

Endometrium-originated oxytocin can possibly stimulate myometrium and have a negative impact on embryo implantation. Inhibition of oxytocin receptors has been shown to reduce uterine contraction frequency in non-pregnant women. Atosiban has been studied on assisted reproductive technologies in the last decade and has been shown to be effective on increasing implantation and clinical pregnancy rates. However, previous studies have used a 37,5 mg total dose of atosiban which was used both before and during embryo transfer. We aim to use a single and low dose of 6,75mg atosiban only before embryo transfer, which is simpler and cheaper and the medication given to patient is significantly lower. If we can demostrate the positive effect of our protocol, it can be suggested to be used routinely in all in vitro fertilization cycles. Additionally, our study is an original study in terms of being the first randomized clinical trial studying the effect of atosiban on frozen-thawed embryo transfer cycles.

Inclusion Criteria:

• Infertile women applied to assisted reproduction clinic
• Follicle stimulating hormone < 12
• Body mass index < 25
• Patients whom antagonist protocol will be used
• Patients whom at least 2 good-quality embryos obtained
• Patients who are volunteer

Exclusion Criteria:

• Severe male factor (Sperm concentration <5 M/ml, progressive sperm motility <%10)
• Uterine anomaly
• Hydrosalphynx
• Difficult embryo transfer
• Patients who previously had a diagnosis of endometriosis and / or adenomyosis
• Endocrine problems (hypothyroidism, hyperthyroidism, hyperprolactinemia, premature ovarian insufficiency)
• Having more than 3 in vitro fertilization failure
• Refusing to participate