The purpose of this prospective cohort study is to assess the effect of endometrial compaction caused by progesterone effect on pregnancy outcomes

For a pregnancy to occur, the embryo must implant in a receptive endometrium during the window of implantation, which is thought to occur from day 22 to 24 of an idealized 28-day cycle. Early studies have suggested that assessing endometrial thickness with the use of ultrasound may be an alternative to invasive techniques such as endometrial biopsy for attempting to determine a receptive endometrium for frozen-thawed embryo transfer (FET).

A preovulatory endometrial thickness of 7 mm or more is considered to be the cutoff for endometrial receptivity, below which many physicians would cancel an embryo transfer. However, in most studies in the literature, endometrial thickness was measured either on the day of hCG in fresh embryo transfer cases or on the last day of estrogen treatment in thawed embryo transfers. There are a limited number of studies evaluating the luteal period, embryo transfer day and endometrial thickness.

Accordingly, in this prospective cohort study is to assess the effect of endometrial compaction caused by progesterone effect on pregnancy outcomes

Inclusion Criteria:

1. Woman aged 18-40 years
2. Presence of high quality (>2BB) blastocyst
3. Hormonal(estrogen and progesterone) frozen- thawed embryo transfer cycles
4. presence of high quality blastocyst cryopreserved by vitrification method.
5. A single embryo transfer

Exclusion Criteria:

1. Presence of uterine pathology
2. Participants whose optimal endometrial image cannot be obtained due to uterine position
3. Participants whose treatments were canceled for any reason before embryo transfer
4. Participants which had embryo transfer on the day 2 or 3 (at the cleavage stage)
5. Participants who had 2 embryo transfer
6. Presence of low quality (<2BB) blastocyst
7. > 15% loss of viability in the embryo during embryo thawing

Female patients underwent infertility treatment

Women underwent frozen embryo transfer