The "biological clock" is a real thing. Female fertility declines sharply in the years preceding menopause. While women have gotten pregnant into their 50s and beyond, it is a rare occurrence—rare enough, in fact, that the medical definition of infertility requires only six months of trying for women over 35, as opposed to a year for younger women. Research has found that the clock runs out when the uterus’s supply of mature ova is depleted. This triggers, through hormonal processes, the start of menopause, though not directly, which is why the decline of fertility happens earlier.
The maturation process by which ova are prepared for release and possible fertilization is called meiosis, in which cells divide to become the ova, which carry half the genetic information necessary to make a person. Researchers have discovered that a molecule called Greatwall kinase is essential to this process. In laboratory animals, it was found that Greatwall kinase plays a role in this division process, and low levels resulted in abnormal, non-functioning ova cells. The research team behind the study believes that the same molecule plays a similar role in human reproduction.
The immune system also plays a role in fertility. For various reasons, most people are born with immunity to certain pathogens already in place, what is called the innate immune system. This generally provides protection against illnesses that were ubiquitous in the ancestral environment and certain illnesses to which the mother’s immune system developed resistance, as opposed to immunity developed during life by the exposure and vaccination. One of the most important components of this innate immune system, a protein called Interleukin-1, also destroys ova, hastening the decline of a woman’s fertility. While the protein cannot be completely eliminated without severely compromising the immune system, doctors believe tat suppressing it can help boost in-vitro fertilization.
In extreme cases, extreme solutions may be necessary. Uterus transplant surgery has been talked about in recent years, and earlier this year the world saw the first success story for this kind of surgery: a woman in Sweden who became pregnant using in vitro fertilization and a transplanted uterus gave birth, at 32 weeks due to complications, but the baby is developing as expected given those complications. In all seven women have received the surgery; this woman is the first to give birth.