Age and Fertility: Understanding How Time Affects Conception and What You Can Do About It

Of all the factors that influence fertility, age is the one that generates the most anxiety and, simultaneously, the most misunderstanding. The relationship between age and fertility is real, measurable, and clinically significant — but it is not the fatalistic narrative often presented in popular media. Understanding the nuances of how age affects fertility empowers you to make informed decisions, take appropriate action, and approach this dimension of your reproductive health with clarity rather than fear.

The Biological Timeline: What Actually Changes with Age

Women are born with their complete lifetime supply of eggs — approximately 1–2 million at birth. By puberty, this number has declined to around 300,000–500,000. From that point, ovarian reserve continues to deplete steadily, with only 400–500 eggs ever actually ovulating across a lifetime. The rest are lost through a process called atresia (natural cell death) that continues regardless of pregnancy, contraceptive use, or health status.

By the late 30s, the rate of follicle loss accelerates. By age 37–38, women reach a threshold after which ovarian reserve declines more steeply. This isn't just about quantity — egg quality also diminishes with age. Specifically, the frequency of chromosomal errors in eggs (aneuploidy) increases substantially:

• At age 25: approximately 10–15% of eggs are chromosomally abnormal
• At age 35: approximately 25–35% of eggs are chromosomally abnormal
• At age 40: approximately 40–50% of eggs are chromosomally abnormal
• At age 43–44: approximately 60–70% of eggs are chromosomally abnormal

Chromosomal errors in eggs are the primary explanation for the age-related increases in miscarriage, IVF failure, and conditions like Down syndrome. They are also why conception becomes harder with age — chromosomally abnormal embryos either fail to implant or are naturally lost early in pregnancy.

What the Statistics Tell Us About Age and Conception

Population-level fertility statistics provide a useful framework, though they represent averages and say nothing definitive about any individual:

• Under 25: approximately 96% of women will conceive within one year of trying
• 25–29: approximately 92% will conceive within one year
• 30–34: approximately 86% will conceive within one year
• 35–39: approximately 78% will conceive within one year
• 40–44: approximately 36–40% will conceive within one year

Miscarriage rates follow the same trajectory. The risk of pregnancy loss is approximately 10–15% at age 25, rising to 20–25% at age 35, 35–40% at age 40, and over 50% at age 44. The majority of these early losses are caused by chromosomal abnormalities and would not have resulted in healthy pregnancies regardless of any intervention.

Advanced Maternal Age (AMA): What "35" Actually Means

The obstetric term "Advanced Maternal Age" (AMA) is applied to pregnant women aged 35 and older. This designation sometimes causes unnecessary distress, as the cut-off of 35 is a clinical convention based on population-level risk thresholds, not a hard biological cliff edge.

What AMA designation means in practice:

• Offered additional prenatal screening or diagnostic testing (NIPT, amniocentesis) due to modestly increased risk of chromosomal conditions
• More frequent monitoring during pregnancy
• Slightly higher rates of intervention in labour and delivery

What it does not mean: that pregnancy is unsafe, unlikely, or inadvisable after 35. The vast majority of women who conceive after 35 — including those in their early 40s — have healthy pregnancies and healthy babies.

AMH Testing and Ovarian Reserve Assessment

Anti-Müllerian hormone (AMH) is produced by small follicles in the ovary and provides an indirect measure of ovarian reserve — the pool of eggs remaining. Unlike other fertility hormones that fluctuate through the cycle, AMH is relatively stable and can be measured on any day.

AMH testing is now widely available as a private blood test and is used by fertility specialists to assess the likely response to ovarian stimulation before IVF, guide timing decisions for women considering future fertility, and investigate potential premature ovarian insufficiency (POI).

A transvaginal antral follicle count (AFC) — an ultrasound count of small follicles in the ovaries — complements AMH and together these two tests provide the most reliable currently available snapshot of ovarian reserve.

When to Seek Help: Age-Adjusted Guidelines

Standard guidance recommends seeking medical evaluation after 12 months of trying for women under 35, and after 6 months for women 35 and over. For women 40 and above, many specialists recommend not waiting at all — an evaluation at the point of decision to try is reasonable.

A basic fertility evaluation typically includes:

• Day 2–3 hormone panel (FSH, LH, oestradiol, AMH)
• Transvaginal ultrasound with antral follicle count
• HSG (hysterosalpingogram) or HyCoSy to assess tubal patency
• Semen analysis for the male partner

IVF and Egg Freezing After 35

For women who are not yet ready to try for a baby but are concerned about age-related fertility decline, egg freezing (oocyte cryopreservation) offers the opportunity to preserve eggs at a younger age for later use. The ideal age window for egg freezing is before 35, though outcomes in the 35–37 range remain reasonable.

For women already trying to conceive who are 38 or older, IVF with preimplantation genetic testing (PGT-A) allows embryos to be screened for chromosomal abnormalities before transfer. This can reduce the time to a successful pregnancy by identifying viable embryos and avoiding transfers of chromosomally abnormal embryos that would not result in live birth.

Supporting Egg Quality Through Nutrition and Supplementation

Coenzyme Q10 (CoQ10)

One of the most well-researched supplements for age-related egg quality decline. CoQ10 is a mitochondrial cofactor involved in cellular energy production. Egg cells are metabolically demanding — they contain more mitochondria than almost any other cell type, and mitochondrial function declines with age. Several fertility specialists recommend beginning CoQ10 supplementation (600mg–800mg daily in divided doses) at least 3–6 months before trying to conceive or beginning IVF.

DHEA

Dehydroepiandrosterone (DHEA) is a weak androgen produced by the adrenal glands. Some IVF studies show improved egg yield and clinical pregnancy rates with DHEA pre-treatment in women with diminished ovarian reserve. However, DHEA should only be used under medical supervision due to its hormonal activity.

Melatonin

Melatonin is a potent antioxidant naturally present in follicular fluid, where it protects developing eggs from oxidative damage. As both melatonin secretion and antioxidant capacity decline with age, supplemental melatonin may offer protective benefit. A dose of 3mg taken at night before IVF retrieval has been studied, with some trials showing improved fertilisation rates.

Comprehensive Preconception Nutrition

A Mediterranean-style diet rich in antioxidants, omega-3 fatty acids, folate, vitamin D, and low in processed foods and trans fats is consistently associated with better reproductive outcomes across age groups.

Paternal Age: The Often-Overlooked Factor

While female age receives the majority of attention, paternal age has increasingly well-documented effects on fertility and offspring outcomes:

• Sperm DNA fragmentation increases with paternal age, associated with higher miscarriage rates and reduced IVF success
• Men over 40 have longer time-to-pregnancy with their partners compared to younger men
• Advanced paternal age (typically defined as 40+) is associated with modestly increased risk of certain conditions in offspring
• Sperm motility and morphology decline progressively from the mid-30s onwards

Frequently Asked Questions About Age and Fertility

Is 35 really a significant fertility turning point?

The age of 35 is a clinically meaningful threshold in a statistical sense — the rate of egg quality decline accelerates around this age, and obstetric guidelines change. However, it is not a cliff edge. Fertility declines gradually throughout the 30s.

Can I improve my fertility at 38 or 40?

You cannot reverse the age-related decline in egg quantity, but you can optimise the quality of the eggs you have through nutrition, supplementation, and removing lifestyle factors that add oxidative stress (smoking, alcohol, poor sleep). These steps genuinely matter.

How accurate is AMH at predicting natural fertility?

AMH is a good marker of ovarian reserve and predicts response to IVF stimulation well. However, it is a poor predictor of natural conception ability in women without infertility. Low AMH in a woman with no other infertility factors may take longer to conceive but does not mean she cannot conceive naturally.

What is premature ovarian insufficiency (POI) and how does it differ from normal age-related decline?

POI (formerly called premature ovarian failure) is the depletion of ovarian reserve before the age of 40. It affects approximately 1% of women and can occur as early as the teens or 20s. Causes include autoimmune conditions, genetic factors, cancer treatment, and sometimes no identifiable cause. POI requires specialist evaluation and management.

Does birth control use affect future fertility?

No. Despite persistent myths, oral contraceptive use does not damage ovarian reserve or future fertility. There is a brief delay in ovulation returning after stopping hormonal contraception, but long-term fertility is not affected.

Is it safe to get pregnant in my 40s?

Many women in their early 40s have healthy pregnancies and healthy babies. The risks — including gestational diabetes, hypertension, and chromosomal conditions in the baby — are elevated compared to younger age groups, but for the majority of women they remain manageable with appropriate prenatal care and monitoring.

Does stress accelerate fertility decline?

Chronic stress does not appear to accelerate the fundamental biology of ovarian ageing or egg loss. However, stress has real effects on reproductive function: it can suppress ovulation, alter cycle length, and reduce sexual frequency. Managing chronic stress is important for overall reproductive health.

What are my options if I'm 40 and have been told my AMH is very low?

Very low AMH at 40 means ovarian reserve is significantly diminished. Options may include: trying naturally with close monitoring, proceeding promptly to IVF with PGT-A, using donor eggs from a younger donor, or exploring surrogacy. A specialist at a reproductive endocrinology and infertility clinic can map out the options specific to your situation.

Can diet and supplements reverse age-related fertility decline?

Diet and supplements cannot reverse the decline in egg quantity. However, they may positively influence the quality of remaining eggs by reducing oxidative stress, supporting mitochondrial function, and optimising the hormonal environment. Think of it as giving your existing eggs the best possible chance, not increasing their number.

At what age should I consider egg freezing?

The optimal age for egg freezing is before 35, when more eggs can typically be retrieved per cycle and egg quality is higher. Freezing before 32 gives the best expected outcomes per egg frozen. Between 35–37, outcomes remain reasonable and freezing can still be worthwhile. After 38, a thorough discussion with a fertility specialist about realistic outcomes is essential.