Like a Virgin by Prasad, Aarathi (recommended reading txt) 📕

large, as we get older, the machinery in most of our cells simply doesn’t work as well; eggs are not the only cells in a woman’s body that go wrong with age, but they tend to be particularly affected by the process. This is because of the way in which egg cells develop. Unlike other cells, some of the eggs in a female foetus may have to wait for fifty years before they are triggered to mature, in readiness for fertilization. While they wait, the chromosomes they contain are lined up in a relatively orderly fashion on what is called a spindle, a structure that forms when a cell is dividing to create two (or four) new cells. The spindle helps guide chromosomes into newly created cells, so that their distribution is equal. Of course, having too many or too few chromosomes can be disastrous for health, so eggs and sperm must only ever contain twenty-three chromosomes or face serious repercussions. While the egg’s chromosomes sit on this spindle, waiting for half a century for their chance, the DNA they carry may well be degrading. The spindle itself may also become damaged, meaning that the chromosomes are not divvied up as neatly as they should be when the egg finally divides. This is partly because, with age, there is also a decline in the levels of certain proteins, called cohesins, that normally hold chromosomes together by entrapping them in a ring – something that’s essential for chromosomes to split evenly when a cell divides. This is one of the reasons why older women are more likely to produce abnormal eggs, which increase the risk of infertility, miscarriage, and birth defects, including the chances of having a baby with Down syndrome.

Down syndrome babies have three full or partial copies (called a trisomy) of chromosome 21, rather than the usual two. Though approximately twenty-five percent of all spontaneous abortions in the first trimester carry chromosome 21 trisomies, the chromosome error alone obviously does not terminate the pregnancy. Indeed, one in every seven hundred babies is born with chromosome 21 trisomy, and it remains the leading cause of learning difficulties and developmental delays in humans. Women with Down syndrome are sometimes able to reproduce. Most men with chromosome 21 trisomy are sterile from birth. Although the exact causes are not known, this infertility may be caused by hormonal deficits, changes to the shape of the gonads, or problems generating sperm.

Other chromosome trisomies are likely to have devastating effects too. For instance, embryos that have one copy or three copies of chromosomes 1 or 19 end up being miscarried before a woman even thinks to perform a pregnancy test. Similarly, in nearly all recorded cases of girls who carry XXX instead of XX in their sex chromosome, the extra X has come from the mother, not the father, and those mothers were usually older than average. Most XXX girls are of normal weight, height, mental function, and fertility, but they tend to experience a very early menopause, around the age of thirty. Somewhat like taking a too-high dose of a medicine, an extra chromosome translates into a too-high dose of certain genes, and abnormally high dosages are ultimately detrimental to a child’s health. In this case, the more X chromosomes a girl carries, the more severe her symptoms will be. That’s not to say that sperm cannot carry this chromosomal corruption, however. There is a significant increase in rogue X chromosomes found in the sperm of older men. A son who carries an extra X chromosome will suffer from Klinefelter syndrome, and will likely have difficulty producing sperm, to some extent; generally, he will be sterile. The condition affects one in a thousand men.

The eggs may be damaged by the environment of the ovaries themselves, which are no longer a safe haven as a woman ages. For example, oxygen levels, pH balance (whether acidic or basic), and hormone concentrations are in flux, and each of these in turn can make it more difficult for the eggs to separate the chromosomes from each other normally in pairs. If the chromosomes stay together rather than splitting apart, then one of the two new cells will have two of the same chromosomes and the other will have none. As the number of eggs ripening in each cycle drops in the run-up to the menopause, there is an increase in chromosomal abnormalities within the eggs. In fact, in IVF programmes the vast majority of eggs that come from women who are thirty-seven years or older have too many or too few chromosomes, as well as mutations in their DNA and in the machinery that controls the way in which this DNA is expressed. For example, ageing eggs are more prone to producing hydatidiform moles, the grossly distorted embryos that result when genes that are normally silent and locked become active, even without the proper imprinting that tells the DNA what to do. When this happens, the renegade DNA behaves as if it has come from the father rather than the mother, so that the embryo is effectively working with two sets of paternal genes. All that can come out of this combination is a mass of tissue inside the womb that, as of now, can never develop into a baby.

An ageing woman’s eggs no longer mature in readiness for fertilization, as younger, healthy eggs normally would, when they are exposed to follicle-stimulating hormone, or FSH. As the menopause approaches, the ovaries stop responding to FSH (they also stop producing oestrogen and progesterone, as we saw earlier). In response, the body produces more and more FSH – ticking and tocking louder and louder. The interactions between the hypothalamus, the pituitary gland, and the ovary change as well. The seamless orchestration of hormones necessary for successful fertilization and pregnancy transforms into