Infertility for which no obvious cause has been found after the following tests have been done with normal results: a sperm count or postcoital test; a test of ovulation, such as a serum progesterone that is satisfactorily high; and a laparoscopy (used to show that the tubes are open and that there is no endometriosis or other obvious abnormality). Although a hysterosalpingogram (HSG) can substitute for laparoscopy in excluding blockage of the fallopian tubes, an HSG can miss peritubal adhesions and will miss endometriosis. Infertility should not be considered unexplained unless a thorough, careful laparoscopy has been done.

A defect of intestinal absorption caused by abnormal sensitivity to gluten in the diet that can first manifest with recurrent miscarriage or unexplained infertility, despite an absence of diarrhea or other disturbances of bowel function. Diagnosis is suggested by serum antigliadin antibodies and serum tissue transglutaminase (or endomysial) antibodies, but requires biopsy of the lining of the small intestine via gastroscopy for confirmation. Responds to a gluten-free diet.

One of the two most important variables (the other is time left for conception) that determines the chance of still getting pregnant naturally in subfertility, including unexplained infertility. The longer the duration of infertility, the smaller the chance each month as time goes on. See also fecundability and time to pregnancy.

Literally, pathology of the embryo (or fetus). Can underlie a miscarriage or, if it reflects are more or less permanent state, can cause unexplained infertility.

Technical speak for the monthly chance of pregnancy, or monthly fertility rate, either for an individual (measured over time) or for a population (the number of conceptions occurring in one month). For any individual with unexplained infertility and in milder cases of subfertility, chiefly determined by the duration of infertility (or, in cases of secondary infertility, in which past fecundability is being estimated, determined by time to pregnancy). Once calculated this way, an estimate of the chance of still getting pregnant naturally (as opposed to undergoing assisted conception) will chiefly be determined by the time left for conception.

A new term for the normal cessation of female fertility up to 10 years before the menopause, being apparent in some women after the age of 33 and most women by 45. Different from the perimenopause, which occurs as egg numbers fall far enough to cause shortening of the menstrual cycle, particularly the follicular phase, and accompanied by elevation of serum FSH when measured during menstruation. If pregnancies are attempted through the oopausal transition, a woman who has had no prior reproductive disturbance will typically experience recurrent miscarriages before developing otherwise unexplained infertility, manifesting in the IVF lab sequentially with unexplained implantation failure of apparently satisfactory embryos, then, in turn, a decreased rate of forming blastocysts, defective cleavage, and then failure of fertilisation. There is no known method of overcoming its effects short of egg donation, except for some hope that the procedure of cytoplasmic transfer might be helpful.

One of the two most important variables that determine the chance of still getting pregnant naturally in subfertility and unexplained infertility (the other is duration of infertility). The longer the time still available the better the chance that, sooner or later, pregnancy will happen. Broadly limited by the female partner's age, but personal circumstances and ambitions within the biologically available timeframe might shorten it, leading to a decision to seek treatment with assisted conception.