This study is intended to determine whether there is a correlation between endometrial compaction and serum progesterone levels on the day of frozen embryo transfers by using transvaginal sonography for the endometrial assessment.

This study is planned to be conducted by prospectively evaluating approximately 200 frozen embryo transfers within 6 months in a single center. Patients planned to be included in the study are started estrodiol 6 mg / day on day2-3 of mensturation. 12 days after the start of estrogen, patients who have endometrial thickness over 7 mm are then started vaginal progesterone supplementation as per routine practice and are eventually proceeded to embryo transfer either on day 4 or 6 of progesterone supplementation. In this study investigators are intended to measure endometrial thickness transvaginally on the day of embryo transfer to accurately determine the presence of endometrial compaction, assess serum progesterone levels, evaluate any possible correlations between endometrial compaction, serum progesterone levels and pregnancy rates.

Inclusion Criteria:

1. Woman aged 20-40 years
2. Hormonal(estrogen and progesterone) frozen- thawed embryo transfer cycles
3. Having available blastocyst(s) cryopreserved by vitrification method.

Exclusion Criteria:

1. Recurrent implantation failure
2. Recurrent pregnancy loss
3. Presence of uterine pathology
4. Requirement for fresh embryo(s);
5. Presence of any clinically relevant systemic disease contraindicated for assisted reproduction or pregnancy
6. Allergy history for relevant drugs
7. Body mass index of <18 or >38 kg/m2 at screening
8. Current breastfeeding or pregnancy
9. Refusal or inability to comply with the requirements of the protocol for any reason, including scheduled clinic visits and laboratory tests
10. Natural or modified natural cycles

Female patients underwent infertility treatment

Women underwent frozen embryo transfer