Progesterone elevation on the day of induction of final maturation is associated with lower pregnancy rates in IVF cycles in women undergoing ovarian stimulation using GnRH analogues and gonadotrophins.[23] At this time, compared to a progesterone level below 0.8 ng/ml, a level between 0.8 and 1.1 ng/ml confers an odds ratio of pregnancy of approximately 0.8, and a level between 1.2 and 3.0 ng/ml confers an odds ratio of pregnancy of between 0.6 and 0.7.[23] On the other hand, progesterone elevation does not seem to confer a decreased chance of pregnancy in frozen–thawed cycles and cycles with egg donation.[23] 

In the US, up to 20% of infertile couples have unexplained infertility. In these cases abnormalities are likely to be present but not detected by current methods. Possible problems could be that the egg is not released at the optimum time for fertilization, that it may not enter the fallopian tube, sperm may not be able to reach the egg, fertilization may fail to occur, transport of the zygote may be disturbed, or implantation fails. It is increasingly recognized that egg quality is of critical importance and women of advanced maternal age have eggs of reduced capacity for normal and successful fertilization. Also, polymorphisms in folate pathway genes could be one reason for fertility complications in some women with unexplained infertility.[59] However, a growing body of evidence suggests that epigenetic modifications in sperm may be partially responsible.[60][61]

A study presented at the British Fertility Society Annual Conference and covered by The Guardian reported that transferring two embryos where one is of poor quality would reduce the chance of pregnancy by 27%. It is thought that a bad embryo is rejected by the endometrium, compromising the implantation of both embryos. Cumulative research has supported the notion that egg quality outweighs quantity.

If both partners are young and healthy and have been trying to conceive for one year without success, a visit to a physician or women's health nurse practitioner (WHNP) could help to highlight potential medical problems earlier rather than later. The doctor or WHNP may also be able to suggest lifestyle changes to increase the chances of conceiving.[62]
Most couples develop a willingness to conceive a child at some point in their life. Generally, couples conceive within the first year, and around 7% of couples conceive in the second year. The inability to conceive within 12 months is defined as infertility. It is recommended to seek help from a reproductive endocrinologist if you are unable to conceive within 12 months. Our modern technology in healthcare has opened a lot of options for women who are facing infertility issues.

A genetic disorder. If you or your partner is at risk of passing on a genetic disorder to your child, you may be candidates for preimplantation genetic testing — a procedure that involves IVF. After the eggs are harvested and fertilized, they're screened for certain genetic problems, although not all genetic problems can be found. Embryos that don't contain identified problems can be transferred to the uterus.