Secondary infertility is the inability to conceive a child or carry a pregnancy to full term after previously giving birth. To classify as secondary infertility, the previous birth must have occurred without help from fertility medications or treatments, like in vitro fertilization. Secondary infertility typically is diagnosed after trying unsuccessfully to conceive for six months to a year. A related condition is recurrent pregnancy loss where patients and couples are able to conceive but are unable to carry to term.
In humans, infertility is the inability to become pregnant after one year of intercourse without contraception involving a male and female partner.[2] There are many causes of infertility, including some that medical intervention can treat.[3] Estimates from 1997 suggest that worldwide about five percent of all heterosexual couples have an unresolved problem with infertility. Many more couples, however, experience involuntary childlessness for at least one year: estimates range from 12% to 28%.[4] Male infertility is responsible for 20–30% of infertility cases, while 20–35% are due to female infertility, and 25–40% are due to combined problems in both parts.[2][5] In 10–20% of cases, no cause is found.[5] The most common cause of female infertility is ovulatory problems, which generally manifest themselves by sparse or absent menstrual periods.[6] Male infertility is most commonly due to deficiencies in the semen, and semen quality is used as a surrogate measure of male fecundity.[7]

We know this is a touchy subject, but unfortunately, there’s no way around it. Science says that age does play a role in fertility. This 2018 study correlated age as a statistically significant factor in secondary infertility compared to primary infertility. In the study, the average age of couples was higher among those experiencing secondary infertility.
A risk of ovarian stimulation is the development of ovarian hyperstimulation syndrome, particularly if hCG is used for inducing final oocyte maturation. This results in swollen, painful ovaries. It occurs in 30% of patients. Mild cases can be treated with over the counter medications and cases can be resolved in the absence of pregnancy. In moderate cases, ovaries swell and fluid accumulated in the abdominal cavities and may have symptoms of heartburn, gas, nausea or loss of appetite. In severe cases patients have sudden excess abdominal pain, nausea, vomiting and will result in hospitalisation.
Additionally, couples may turn to assisted reproductive technology, the most common of which is in vitro fertilization (IVF). Other techniques may include special injections or using a donor's eggs or sperm. Complications can sometimes occur, the most common being bleeding or infection; ovarian hyperstimulation syndrome, in which the ovaries become swollen and painful; and multiple pregnancies.

Luteal support is the administration of medication, generally progesterone, progestins, hCG, or GnRH agonists, and often accompanied by estradiol, to increase the success rate of implantation and early embryogenesis, thereby complementing and/or supporting the function of the corpus luteum. A Cochrane review found that hCG or progesterone given during the luteal phase may be associated with higher rates of live birth or ongoing pregnancy, but that the evidence is not conclusive.[79] Co-treatment with GnRH agonists appears to improve outcomes,[79] by a live birth rate RD of +16% (95% confidence interval +10 to +22%).[80] On the other hand, growth hormone or aspirin as adjunctive medication in IVF have no evidence of overall benefit.[30]