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How Does Age Impact Fertility in Both Men and Women?

Age is one of the most important factors that impact human fertility in both sexes. Fertility gradually declines in both men and women as they get older, though the timeline differs between the genders. Understanding how advancing age affects reproductive abilities can help couples make informed family planning choices.

This extensive article will cover how ovarian reserve, egg quality, ovulation, and pregnancy risks change with age in women, as well as how sperm parameters, testosterone levels, and DNA integrity decline with age in men. Key statistics and tips for preserving fertility potential while ageing will also be provided.

Overview of Fertility and Age

Overview of Fertility and Age
Source: sofatinfertility.com
  • Both men and women are born with a finite number of reproductive cells – eggs and sperm. This fertile reserve declines over time.
  • Women experience a more abrupt fertility decline around age 35-40 associated with reduced ovarian reserve and egg quality. This coincides with the transition to menopause, when periods cease.
  • Male fertility gradually declines starting around age 40-45 but does not fully halt like the female menopause. Older men remain able to father children into advanced age, although risks exist.
  • Environmental toxins, illness, obesity, smoking, alcohol use, and other lifestyle factors can accelerate the natural age-related decline in fertility.
  • Education about how age impacts fertility empowers couples to make informed family planning and health decisions.
  • Options exist to evaluate fertility potential through testing of ovarian reserve, semen analysis and hormone levels to detect issues.
  • Fertility preservation options like egg freezing for women and sperm banking for men may be considered.

Understanding the complex effects age has on reproductive function helps men and women proactively maintain their fertility potential as long as possible while also making wise choices about optimal timing for family building.

How does Ovarian Reserve Decline With Age in Women?

ovarian-reserve-by-age
Source: invitra.com

Ovarian reserve refers to the number and quality of remaining oocytes (immature eggs) in a woman’s ovaries. Women are born with approximately 1-2 million eggs, which declines over their lifespan. By puberty, only about 300,000-400,000 eggs remain. Throughout adulthood, no new eggs are generated, only lost monthly through ovulation and atresia (degeneration).

Ovarian ageing progresses through these milestones:

  • Menarche – First menstrual period in adolescence as fertility blooms
  • Peak fertility – Optimal egg quality in teens through mid 20s. Chance of conception each cycle – 25-30%
  • Subtle decline – Gradual drop in ovarian reserve from late 20s to mid 30s. Greater month-to-month variability in number of eggs ovulated. Chance of conception each cycle drops from 20-25% at age 30 to 12-15% by age 35. Often not perceptible.
  • Accelerated decline – Rapid depletion of the ovarian reserve from the mid to late 30s. The chance of conception each cycle further drops to only 5% by age 40.
  • Menopause – Complete cessation of menstrual periods indicating no remaining ovarian follicles. The average age is 51 in U.S. Occurs between ages 45-55.

The ovarian reserve comprises primordial follicles containing immature eggs. Each month, a cohort grows and matures, but only one dominant follicle fully develops and ovulates an egg. The remaining follicles involute. With ageing, the number of responsive follicles diminishes as egg quality also deteriorates.

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By age 30, approximately 90% of the original eggs are depleted. By age 40, only about 25,000 eggs remain. With menopause, less than 1,000 eggs persist. This explains the marked fertility decline. Augmenting the age-related loss are declines in hormone levels and increases in chromosomal abnormalities.

How does Egg Quality Decline with Age in Women?

Egg Quality Decline with Age in Women
source: medicalnewstoday.com

Egg quality diminishes with age, reflected by higher rates of:

  • Aneuploidy – Chromosomal abnormalities
  • Mitochondrial mutations – Errors in the cell’s energy generators
  • Fragmented DNA – Damage to the egg’s genetic material
  • Cellular dysfunction – Suboptimal energy production
  • Higher granulosa cell death – Supporting ovarian cells die off

This may be attributable to:

  • Accumulated oxidative stress – Toxins like smoking generate harmful free radicals
  • Shortened telomeres – Protective caps on DNA strands deteriorate
  • Declining levels of cohesin proteins – Needed to separate chromosomes properly during cell division
  • Inefficient DNA repair mechanisms – Critical for correcting genetic typos
  • Deteriorating meiotic spindles – Machinery segregating chromosomes decays
  • Epigenetic changes – Chemical markers on DNA go awry
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The impact shows in elevated rates of:

  • Aneuploidy – 65% in women over 40 versus 35% in women under 35
  • Oocyte chromosomal abnormalities – 13% under 35, 25% 35-37, 61% over 42
  • Miscarriage – Rises from 10% under age 35 up to 80% by age 45
  • Stillbirth – Rates double from age 35 to 42
  • Gestational diabetes – Increased 6X from age 25 to 42
  • Placenta previa – Increased 6X from age 25 to 42
  • Low birth weight – Increased 2X from age 25 to 42

So, both reduced ovarian reserve and reduced oocyte quality culminate in poorer reproductive outcomes with ageing. This results from an interplay of many molecular and cellular changes.

Why Does The Risk of Congenital Disabilities Increase with Maternal Age?

Why Does The Risk of Congenital Disabilities Increase with Maternal Age
source: mdpi.com

The rise in chromosomal abnormalities and DNA damage in ageing eggs significantly increases the risks of certain congenital disabilities with advancing maternal age:

  • Down syndrome – Caused by an extra copy of chromosome 21. Risk rises 12-fold from age 25 to 40. From 1 in 1250 births to 1 in 100 births. Accounts for about one-third of all congenital disabilities.
  • Patau syndrome – Result of extra chromosome 13. Occurs in 1 in 10,000 births at age 25, versus 1 in 300 births by age 40. Frequently fatal soon after birth.
  • Edwards syndrome – Extra chromosome 18. Risk increases from 1 in 8000 births at age 25 to 1 in 350 births by age 45. Most do not survive infancy.
  • Turner syndrome – Missing X chromosome, only have one instead of two. About 1 in 2000 births to women under 25 versus 1 in 25 by age 45. It is characterized by short-stature infertility.
  • Klinefelter syndrome – Extra X chromosome in males causing infertility. 1 in 2000 births under age 30 versus 1 in 400 births over age 50.
  • Rare trisomies – Extra copies of chromosomes 16, 22, and others also rise with age. Usually, it is not compatible with life after birth.
  • Structural defects – Heart, limb and neural tube defects increase with age. 2-3X higher over age 40.
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Proper chromosomal segregation is crucial for normal development. Age-related meiotic errors in maturing eggs significantly increase DNA abnormalities, leading to heightened rates of genetic syndromes and anomalies. This underlies the strong correlation between maternal age and congenital disabilities.

Can Older Women Still Conceive Naturally and Have Healthy Pregnancies?

chances-of-getting-pregnant-by-age
source: Shecares.com

Absolutely. While female fertility progressively declines and risks of pregnancy complications increase with age, conceiving and carrying a healthy pregnancy is still very possible into the 40s:

  • Up to one-third of couples with a woman over 35 will conceive naturally within 6 months. But may require up to 2 years.
  • In women aged 35-40, the monthly probability of conception is 5-10%. By 45, it drops to 1%. But not zero.
  • About 20% of women over 35 will not succeed in conceiving naturally but can with assisted reproductive technology.
  • By age 45, rates of pregnancy loss exceed 80%. But 15-20% of conceptions remain viable.
  • At age 45, the odds of miscarriage are 50% by week 10 and 75% by week 20. However, some pregnancies progress successfully.
  • Risk of stillbirth doubles from age 35 to 42. But remains only 1-2% up to age 45.
  • Most age 45+ pregnancies today result from donor egg IVF. But a few thousand women still conceive using their eggs every year.
  • Risks of gestational diabetes, preeclampsia, and cesarean delivery steadily climb. But can be well managed under obstetrician care.

So, while maternal age impacts the ease of conception and risks during pregnancy, women in their 40s can and do still experience healthy pregnancies and deliveries. Close monitoring and proactive management of risks is recommended. Talk with your doctor about your overall health status, not just age.

What Options Exist for Older Women Seeking Pregnancy?

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Women desiring pregnancy in their later reproductive years have a few options to consider:

  • Continue trying to conceive naturally – Have sex at least twice a week, ideally every 2-3 days. Monitor cycles and ovulation to time intercourse.
  • Use assisted reproductive technology – IVF with your own eggs or donor eggs, IUI, fertility drugs. Success rates vary widely based on age and egg quality.
  • Consider an egg donor – Using a younger donor’s eggs can increase IVF success rates from ~5% with own ageing eggs to 60-70% with a donor.
  • Adopt or foster a child – Provides the chance to raise a family when pregnancy Is not possible or advisable.
  • Use a gestational surrogate if uterine issues exist – Your partner or a donor’s sperm is used to fertilize a donor egg, then transferred to the gestational carrier’s uterus.
  • Acceptance of childfree lifestyle – Shifting mindset if parenthood cannot be obtained. Finding meaning in relationships with partners, relatives, friends and communities.

There are still paths to parenthood into the 40s, but proactive steps must be taken as fertility declines. Working with both a reproductive endocrinologist and a mental health counsellor helps navigate this challenging life transition.

Related Post: Can depression cause male infertility?

How does Seminal Quality Decline with Age in Men?

Seminal Quality Decline with Age in Men

Unlike the clear fertility decline in women, male reproductive potential decreases gradually with age. Sperm production continues lifelong, but parameters slowly decline, including:

  • Volume – Seminal ejaculate fluid decreases ~3% per year from age 30 onwards.
  • Sperm concentration – Number of sperm per mL declines ~2% annually after 35 years old. Drops from 100 million/mL to only 10-20 million/mL in men over age 60. Marks a slower gradual decline versus women.
  • Motility – Fraction of sperm with active movement drops ~0.7-1% yearly. Decline accelerates over age 60.
  • Morphology – The rate of normally shaped sperm decreases by ~0.2% per year from 35-80 years old. Higher risk of malformed sperm.
  • DNA integrity – Sperm DNA damage accumulates. Impairs embryo development potential.

Unlike the clear fertility loss in menopause, male fertility does not suddenly halt. However, the gradual quantitative drop and decline in sperm quality mean fertility rates do decrease with paternal age.

Does Paternal Age Increase Congenital Disability Risks Like Maternal Age Does?

Advancing paternal age raises risks of certain rare congenital disabilities:

  • Achondroplasia – a skeletal disorder causing dwarfism – risks triple from age 30 to 50.
  • Apert syndrome – premature skull bone fusion – increases 7X from age 30 to 50.
  • Costello syndrome – intellectual disability, abnormal growth – 10X higher risk.
  • Marfan syndrome – connective tissue disorder.
  • Osteogenesis imperfecta – brittle bone disease.
  • Autism – 50% higher incidence over age 50. This is likely due to higher gene mutations.

However, the syndromes linked to older fathers are rarer versus chromosomal defects tied to older mothers. Overall, congenital disability risk only rises from about 3% to 4% from paternal ages 35 to 45+. The exact mechanisms behind increased congenital disability rates require further study but likely involve sperm gene mutations.

Why Does Time to Conception Increase with Male Age?

Why Does Time to Conception Increase with Male Age
source: longdom.org/
  • Older men take longer to achieve pregnancy on average – This reflects the declining semen parameters—but also lower sexual frequency and sometimes erectile dysfunction.
  • When controlling for the woman’s age – Couples take 2X longer to conceive when the man is over 35 versus under 35.
  • If the man is over 40 – It takes 3X longer to achieve pregnancy versus both partners under 30.
  • For men over 45 – It can take 4-5X longer on average versus men under 30 if the female partner is younger. But it’s still very possible.
  • Semen analysis results in decline – Lower volumes, concentration, motility and morphology.
  • DNA damage accumulates – sperm gene mutations rise with paternal age.

So, while male fertility only declines subtly, by the 40s-50s, the additive effect of the multiple changes means a longer average time to conception. But since spermatogenesis continues and some normal sperm remain, older fathers can still often succeed, just at lower rates versus their peak fertility years.

At what Age are Women and Men Most Fertile?

At what Age are Women and Men Most Fertile?
Source:britishfertilitysociety.org.uk
  • Peak fertility age for women is the mid-20s. Egg quality, hormone levels and monthly chances of conception are highest.
  • Peak fertility age for men is also the mid to late 20s. Sperm parameters like count, motility and morphology are optimal.
  • By age 30, fertility starts declining subtly in both genders but is still robust. 85% of couples conceive within a year.
  • Fertility for both women and men remains strong through the early 30s. Chances of conception each cycle are 20-25% monthly at this age.
  • After age 35, fertility drops faster. Monthly conception rates fall to 10-15% by the late 30s—longer to conceive and higher miscarriage risks.

While fertility peaks for both sexes in the mid-20s, significant decline is only detectable after age 35. So, both women and men retain excellent odds of conception through their early 30s without a major impact of age. But from the mid to late 30s, age-related fertility issues emerge.

Tips for Preserving Fertility During Ageing

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Though fertility inevitably declines with age, certain preventative habits may help slow deterioration:

  • Maintain normal BMI – Obesity or underweight exacerbates hormone changes
  • Regular exercise – Improves hormonal balance and sperm quality. Moderate is ideal – not excessive.
  • Healthy diet – Particularly antioxidant foods to reduce free radical damage to eggs and sperm
  • Stress management – High stress and cortisol negatively impact fertility
  • Limit toxin exposures – Cigarette smoke, pesticides, BPA plastics, heavy metals
  • Avoid STIs – Chlamydia and gonorrhoea can cause reproductive damage
  • Take a prenatal vitamin with folate – Improves egg and sperm cell production
  • Manage chronic illnesses – Thyroid disorders, diabetes, and autoimmune diseases
  • Annual checkups to monitor hormone levels – Testosterone, FSH, estradiol, AMH

While we cannot halt the natural ageing process, optimizing lifestyle factors provides the best chance of preserving fertility over time. But the age-related decline remains inevitable. Planning family building earlier when feasible is ideal biologically. Elective egg freezing in the 20s-early 30s is an option to consider for women. Discuss the impact of age on fertility with your doctor.

Conclusions on How Age Affects Fertility

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  • Ovarian reserve – quantity and quality of remaining eggs – declines acutely as women transition through menopause, with rapid fertility loss in the late 30s/early 40s.
  • Male fertility decreases in a more gradual, subtle manner with advancing age but does not fully cease like in women. Sperm quality declines modestly each year.
  • Peak fertility for both women and men spans the mid-20s to early 30s. Significant age impacts on fertility arise more prominently from the 30s and beyond.
  • The maternal age effect strongly increases risks of genetic disorders like Down syndrome. Paternal age also increases some rarer congenital disability rates.
  • Older women and men can still often conceive naturally into their 40s but pursue parenthood earlier if possible for optimal fertility. Elective egg/sperm freezing can preserve fertility.
  • Maintaining reproductive health through lifestyle habits like avoiding STIs, toxins, and obesity provides the best odds of preserving fertility during ageing.

The dual impacts of lowered reproductive cell reserve and deteriorating egg/sperm cell quality culminate in the age-related fertility decline. But hope and options exist to achieve pregnancy even in the later reproductive years.

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