INCLUSION CRITERIA:  In order to be eligible to participate in this study, an individual must meet all of the following criteria:  Stated willingness to comply with all study procedures and availability for the duration of the study Female, aged 18-42, childbearing potential  In good general health as evidenced by medical history, previous fertility or diagnosed with infertility with and without a previous pregnancy loss.  Normal Fertile - Control- Women with proven parity based on spontaneous conception without fertility treatment or prior diagnosis of infertility, normal uncomplicated pregnancy, and birth of at least one healthy baby ART Infertile - Control-Women that are part of a couple diagnosed with unexplained infertility that conceived on the first embryo transfer (ET) attempt and meet inclusion/exclusion criteria.  Early Implantation Failure (EIF) - Infertility defined by a failure to conceive after:  a) three or more failed transfers of high-quality blastocyst(s) (grade 3BB or higher); or b) two or more transfers of euploid blastocyst(s) (tested through trophectoderm biopsy and preimplantation genetic testing for aneuploidy (PGT- A) using next generation sequencing). These women will have a negative serum beta human chorionic gonadotropin (hCG) 12 days after ET.  Early Pregnancy Failure (EPF) - Infertility defined by two or more biochemical pregnancies after transfer of a high-quality or euploid blastocyst with a positive hCG 12 days after ET but without subsequent clinical signs of pregnancy (detection of intrauterine or extrauterine gestational sac at 5-7 weeks of gestation). While, by definition these are pregnancies of unknown location (PUL) and will  include spontaneously resolving ectopic pregnancies, the vast majority of these will be failed intrauterine pregnancies.  --Recurrent Pregnancy Loss (RPL): Infertility defined by the loss of two or more pregnancies after transfer of a high-quality or euploid blastocyst with a positive HCG 12 days after ET and subsequent clinical signs of pregnancy (detection of an intrauterine gestational sac at 5-7 weeks gestation by ultrasound).  Exclusion Criteria:  An individual who meets any of the following criteria will be excluded from participation in this study:  Women with prior hysterectomy as they do not have an endometrium Postmenopausal women Women with a history of preterm delivery (<37-week gestation), preeclampsia and/or stillbirth are excluded. Women with RPL must screen negative for the antiphospholipid syndrome (negative lupus anticoagulant, negative IgG and IgM antiphospholipid antibodies and negative IgG and IgM anti-2GP1 antibodies) Women suffering from infertility with and without early pregnancy loss with prior diagnosis of common known disease risk factors, including disorders such as uterine anomalies, coagulopathy, balanced translocation, gynecological disease, other reproductive disorders and/or autoimmune conditions, pathology confirmed or suspected endometriosis, pathology confirmed or suspected adenomyosis, endometrial polyp(s) or submucosal fibroids, pathology confirmed acute or chronic endometritis, hydrosalpinx communicating with the endometrial cavity, history of Asherman syndrome, poorly controlled endocrinopathies, HIV infection, ovarian insufficiency and irregular menstrual cycles Women who are currently Pregnant as we would not be able to obtain an endometrial sample History of gonadotoxic therapy, precancerous (endometrial hyperplasia) or cancerous condition of the female reproductive tract, Current smoker or tobacco use or tobacco use within 30 days. Current use of reproductive hormones and/or fertility medications Current use of steroids or non-steroidal anti-inflammatory agents within the last 3 days. Women who are obese (BMI >30)