How Old Is Too Old to Have a Baby for a Woman

How far can female fertility be extended?

(Epitome credit:

Press Clan

)

Modern medicine is already allowing women to have children far later in life than their ancestors, simply how far tin female person fertility really be extended?

"It'due south one of nature's great inequities," says Dagan Wells, professor of reproductive medicine at the University of Oxford. He is referring to the progressive, and largely irreversible, turn down in female fertility from the age of 35 years onwards.

Men besides feel a decline in their babe-making ability as they get older, but this fall in fertility tends to commencement afterwards and occur much more slowly than in women. The fertility rate for men tends to begin falling around the age of 40-45 years old.

But when exactly does a adult female's fertility beginning declining? And when does that refuse result in the end of natural fertility?

For millennia, women accept been getting pregnant and bearing children in their teens and early 20s – non much different from the Krapina Neanderthals, living in Northern Republic of croatia 30,000 years ago, whose fossilised remains advise gave nativity to their outset child at 15 years of age. Prior to the 1960s, women in the United states were having their first child on boilerplate at effectually the age of 21.

You lot might also like:

• The scientist who changed human fertility
• What if women had total command over pregnancy?
• The upshot of childbirth no-one talks about

In 2017, however, the boilerplate age of mothers giving birth in all OECD countries was 30. Simply under half (44%) of all alive births in England and Wales in the same yr were to mothers anile 30 while the average historic period of women giving nativity to their offset kid in South korea was 31.

Fertility treatments and the ability to freeze eggs has allowed more women to have children later than was possible in the by (Credit: Science Photograph Library)

But what does this hateful in the context of the ticking clock of female fertility?

Numbers matter

For decades, scientists have associated the turn down in female person fertility with the historic period-related decrease in the number of eggs contained within a woman's ovaries. Each, if fertilised, has the potential to grow into a infant.

Different men, whose reproductive organs produce millions of fresh sperm on a daily basis, women are born with all the eggs that they will ever possess. Moreover, this number steadily declines as a woman ages: from ane one thousand thousand eggs at nativity to 300,000 by puberty, 25,000 by the age of 37 and 1,000 by the age of 51. Of all these, however, but 300 to 400 eggs with baby-making-potential – unremarkably only 1 a month – will mature and somewhen be released from a woman'southward ovaries through ovulation beyond her entire life. For reasons not yet fully understood, the remainder undergo a natural process of degeneration and will never be ovulated.

Most girls begin menstruating betwixt nine and 13 years of historic period, just their ovaries don't start releasing eggs until a least a yr or ii later. Elementary mathematics would propose a woman's egg supply would then typically exhaust itself effectually 33 years afterward. And in about women, fertility does indeed tend to cease up to eight years earlier the onset of menopause, which for American women is around the time of their 51st altogether.

While such crude calculations practice not take the natural variability that tin exist between women into business relationship, or the fourth dimension windows during which ovaries might release more ane egg in a month, or months in which no egg is released at all, they can give a rough estimate of but how long the female fertility timeline tin can be.

A more precise estimate of a woman'south egg count, likewise known as "ovarian reserve", can exist obtained by measuring the level of hormone called anti-Mullerian hormone (AMH) in a woman's blood. We now know that AMH, produced past the ovaries of fertile, developed women, plays a vital role in the metamorphosis of an immature egg prison cell into a mature, hopeful egg, complete with all the biological prerequisites to create a healthy baby. Better functioning ovaries, with larger egg stores, produce more than AMH.  Levels of the hormone decline as the timeline of female person fertility progresses – average levels in 30 to 35 year olds are roughly ii-thirds that of younger women while levels in women aged over 45 years are a quarter of those seen in women in their 20s.

When they are born, women's ovaries already contain all the eggs they will ever produce (Credit: BBC)

Andrea Jurisicova, an embryologist at the Lunenfeld-Tanenbaum Research Institute of Mount Sinai Infirmary, has spent years studying the mechanisms that underpin the decline in female fertility with age, and investigating what can be washed to slow this. Her enquiry has found that ovarian reserve is genetically regulated but that a woman's life experiences – such equally stress, exposure to radiations or toxic chemicals and even those from when she herself was in the womb – determine egg numbers in subsequently life.

Quality matters

But female fertility isn't only about the quantity of eggs. Quality matters too, and is much more than technically challenging to assess than egg numbers. While egg counts decline equally women age, and so does the quality of the chromosomes and the Dna contained within each egg.

"Chromosomal abnormalities in human eggs are extremely common," says Wells. "It'southward not something that should exist considered to be a peculiarly abnormal situation, and in most cases its something that all women, even young women, will have in their eggs at a depression level merely that level increases with advancing historic period."

For a woman in her 20s, a quarter of her eggs may be expected to have chromosomal abnormalities – this increases to up to 40% for a woman betwixt 30 and 35, and "goes upwards merely exponentially from in that location on". Beyond the age of 35, the frequency of these chromosomally abnormal eggs increases by 0.5% per month, so that for a woman in her early on 40s up to three-quarters of her eggs will have chromosomal abnormalities.

Having chromosomal abnormalities in her eggs doesn't necessarily hateful a woman is infertile, but they do mean that more than of her menstrual cycles will produce eggs that are less likely to produce a feasible infant.

Chromosomes are bundles of tightly coiled Deoxyribonucleic acid that agree the genetic information needed for an organism to develop. A human egg contains 23 chromosomes – the half of your genetic code that comes from your mother – which needs to combine with the 23 chromosomes from your male parent's sperm to develop into a viable embryo. An egg with too many or too few chromosomes, broken or damaged chromosomes will ofttimes fail to develop properly. In some cases a baby can still be born with chromosomal abnormalities, as happens with Downward's Syndrome.

But most chromosomal abnormalities tend to be lethal to the extremely immature embryo, resulting in the embryo failing to implant in the lining of the womb or a very early miscarriage, often between five and viii weeks of pregnancy.

While the risk of chromosomal abnormalities is known to be higher in the eggs of older women, a recent European study establish that the level of chromosomal abnormalities is too high in younger women as well – from thirteen into their early 20s. The findings suggest that female person fertility timeline follows a northward-shaped pattern, with elevation fertility observed in the mid-20s and lower levels of fertility both in very young and older women.

Older mothers may face greater risks during pregnancy, labour and commitment, but at that place are problems associated with older fathers too (Credit: Getty Images)

Elsewhere in the egg, faulty mitochondria – the tiny power stations that provide energy for our cells and which we all inherit from our mothers – can also be a problem in older women. Studies take shown that upwards to half the eggs of women who are older than 35 comport mutations in their mitochondrial DNA, compared to a tertiary of the eggs in younger women.

"An egg needs a threshold of about 40,000 mitochondrial Dna copies to make an embryo," says Jurisicova.

For Wells, the evidence is clear.

"The rate of decline accelerates around the historic period of 35 and the vast majority of women are essentially infertile by the time they attain 45," says Wells. "Importantly, this is years, maybe even a decade, before menopause. Anybody expects to be a little less fertile when yous are older, but the extent of that reject takes a lot of people by surprise."

It would be incorrect to focus only on female fertility. Some studies take shown that sperm quality also declines with age in men, starting in their 20s. Sperm mobility – the ability of information technology to swim around – has been found to pass up by around 0.7% every year while the sperm of older men acquit more mutations in their DNA. Older fathers also pass on more than mutations to their children than mothers do from their eggs.

Best egg

"The human egg is a remarkable and unusual prison cell, it's the biggest cell in the body, and has a unique feature," says Wells. He is referring to the egg'due south ability to terminate halfway through its growth and remain in a state of suspended animation for years, even decades, until it is eventually ovulated. His inquiry suggests that information technology is the egg's ability to agree its chromosomes in a stable configuration during this period of hibernation that governs its power to brand an embryo and a baby.

Jurisicova'due south work adds another piece to the puzzle. Her work suggests that human eggs undergo a process of growth and maturation within the ovary for at least nine months before they are released during ovulation. "The quality of the egg released is the culmination of all the health and environmental influences on that growing egg over the past nine months," she says. Stress, exposure to radiation or toxic chemicals during this fourth dimension tin can take an adverse effects on the developing egg.

It is perhaps interesting that the duration of this incubation period – from when an egg emerges from hibernation and begins developing – uncannily resembles the number of months a babe spends within the womb earlier it is born. During this catamenia of maturation, the egg develops the resources it will need should it be fertilised.

"The egg has to be extremely well resourced," says Wells. "For the first three days post-obit fertilisation the embryo doesn't really make annihilation for itself – information technology doesn't transcribe its genes, it doesn't brand proteins – its completely reliant on what the egg has provided for information technology. A more mature egg is more likely to be better resourced than a less mature one."

While there may be niggling that science can do to change the number of eggs that nature (or genetics) decides a woman will take during her life, Wells and Jurisicova hold there are ways to improve, or rescue, egg quality. Adopting a healthy lifestyle, exercising regularly, reducing stress and making sure that health problems such as hypothyroidism and other autoimmune conditions are well controlled can all help.

The range of factors pitched against an egg being fertilised and developing into a foetus make childbirth seem all the more incredible (Credit: Science Photograph Library)

Jurisicova recently found that giving female mice the antioxidant coenzyme Q10 delivers promising results – the mice that received the supplement produced better quality eggs with more properly aligned chromosomes and amend mitochondrial function. They were also more than successful in producing alive babies, than the mice that did non receive the supplements. The results are, however, yet to be replicated in humans.

The journey, not the destination

Mothers don't but demand to contend with their fertility as they get older, simply also greater risks during pregnancy, labour and delivery. The First and 2d Trimester Evaluation of Risk (Faster) trial, a U.s. written report funded by the US National Found of Child Health and Human Development (NICHD), looked at the health records of over 36,000 women. They found mothers over twoscore were ii to three times more than likely to experience health issues during pregnancy including diabetes and high claret pressure. They were twice equally likely to feel bleeding from their placentas, accept a caesarean commitment and to lose their baby later on on in pregnancy.

The children of older outset-time mothers who are 40 years and above likewise have an increased risk of health bug at birth, such equally low nativity weight and congenital abnormalities. They as well have a 50% increased take chances of beingness born preterm and, perhaps consequently, are at increased risk of requiring neonatal intensive care after birth.

But this is still but one one-half of the equation. Older fathers likewise bring boosted health risks for their children. Babies with older fathers are more likely to be born prematurely, take a lower birth weight and college take chances of seizures. Some studies have also linked increasing paternal age to a greater take a chance of weather such every bit autism and ADHD where the father is over the age of 40, merely the evidence remains inconsistent.

Scientists are developing new techniques to identify the best eggs for use in IVF treatments (Credit: Scientific discipline Photo Library)

Is information technology possible to extend female fertility and for how long? As is often the example, where nature creates inequity, science attempts to level the playing field. In September last yr, Erramatti Mangamma, a 74-year-one-time from southern India go the world'south oldest start-time mother, delivering twin baby girls conceived via In Vitro Fertilisation (IVF) after 57 years of infertility. Iii years ago, 72-year-old Daljinder Kaur, from north Republic of india, gave nativity to a son afterwards nearly five decades of marriage and 2 unsuccessful IVF attempts.

The significant advances in reproductive medicine over the past decades have greatly increased the safety, success, accessibility and affordability of bogus reproductive techniques. Approximately 230 babies are built-in in the Britain each twelvemonth to women aged 50 and over while ix% of all first-time mothers in the The states were aged to a higher place 35 in 2014.

Merely as nosotros have seen, these techniques are nonetheless limited to a degree by the age of the egg. This is, not least, because of the effects of ageing on the DNA, but also considering older eggs accept been exposed to environmental toxins for a longer amount of time. Information technology is possible, of course, for women to undergo IVF using a donated egg from a younger woman. Almost all fertility clinics across the earth now also offer women an option to store their eggs, frozen in time, until she is ready for them to be thawed, fertilised and transplanted into her womb.

"The difficulties experienced with older women trying to take children is not related to the uterus but to the egg, and chromosomal abnormalities are at the heart of that," says Wells. "The egg is the seed rather than the soil. Many of the very early on steps in homo development are determined by what the egg provides."

With the aid of technologies like pre-implantation genetic testing, Wells and his fellow embryologists are developing ways of identifying the best eggs that can be used in IVF treatments. Other techniques such as mitochondrial replacement therapy are also helping mothers with defects in their eggs requite birth to healthy children.

Simply while science is making commendable steps to help prolong the ticking clock of female fertility, information technology may not e'er exist possible to keep it going indefinitely. The refuse of natural female fertility is equally inevitable as it is universal.

--

Join one one thousand thousand Future fans by liking us on Facebook , or follow us on Twitter  or Instagram .

If you liked this story, sign up for the weekly bbc.com features newsletter , called "The Essential List". A handpicked option of stories from BBC Future, Culture, Worklife, and Travel, delivered to your inbox every Friday.

rogerswiltat.blogspot.com

Source: https://www.bbc.com/future/article/20200828-how-fertility-changes-with-age-in-women

Share this post