Prospective cohort multicentric study including infertile patients undergoing a pregnancy test on βhCG day (around ET +11), after an ET in the context of an artificial cycle and receiving LPS with vaginal natural progesterone following the clinical practice in IVI RMA (Spain).

The investigation team have already demonstrated that serum progesterone levels measured on the ET day in artificial cycles are related to pregnancy outcome. In this line, this problem can be countteracted after supplementation with an additional source of external progesterone, achieving similar ongoing pregnancy and live birth rates in women with serum progesterone levels below and above the threshold point determined on the ET day.

Despite this, it has been observed apparent differences on the maintenance of pregnancy in patients with a positive pregnancy test according to their serum progesterone levels measured on day ET+11, which is the same day in which we perform the pregnancy test. These differences seem to be originated due to later higher clinical miscarriage rates in patients with lower serum progesterone levels on day ET+11, despite their positive pregnancy test.

This fact may be due to patientes low serum progesterone levels, insufficient to maintain an ongoing pregnancy. Taking this into account, this study aim to confirm that serum progesterone levels on βhCG day are indeed related to final pregnancy outcome and to evaluate if there is any cut-off point of serum progesterone levels, as we have previously found on the ET day.

Inclusion Criteria:

• The subject must provide written informed consent prior to any study related procedures
• Women ≤50 years old
• BMI ≤ 35 kg/m2
• Adequate endometrial thickness (>6.5mm) and pattern (Triple A structure) in the proliferative phase

Exclusion Criteria:

• Uterine Pathology, adnexal pathology
• Systemic diseases

All infertile patients undergoing an embryo transfer in the context of an artificial cycle will be recruited.