Age and female fertility

• delayed childbearing
• advanced maternal age
• reproductive aging
• oocyte
• ICSI
• IVF
• infertility

People say the word “old” stings even when whispered. So today I want to explain how a woman's age relates to egg quality — and then go further, into what age does to the rest of the reproductive system and to health more broadly.

I once surveyed people walking around the Suan Oi neighbourhood in front of Vajira Hospital to see how many knew that fertility declines with age. Only about 20% had any inkling that age causes trouble. The rest were unsure — some believed a woman can conceive throughout her whole life.

The stages of a woman's reproductive life

In theory a woman's life divides into four reproductive stages — though the number on the birth certificate does not always match the stage she is actually in.

Prepubertal

• From birth until the first period (age 12–13)
• Sex hormones are not yet produced
• The eggs have begun dividing but are arrested at meiosis I

Reproductive years

• From the first period until cycles become irregular (roughly ages 20–45)
• The sex-hormone system works normally
• One egg ovulates each cycle

Perimenopause

• The egg pool is running low
• Periods start to become irregular
• Menopausal symptoms may appear: hot flushes, sweating, poor sleep

Menopause

• Very few eggs remain
• No period for at least 12 months
• Other menopause-related health problems

Egg number and quality with age

The number of eggs peaks at about 20 weeks of gestation, while a girl is still in her mother's womb — roughly two million. From then on it falls steadily. By the first period around 200,000–400,000 remain. After menstruation begins, batches of eggs are constantly recruited, but in each cycle only one matures and ovulates for fertilisation.

Resting eggs have already entered meiosis, the division that halves the chromosome sets. (We normally carry two sets, one from each parent; to pass them on, the germ cell must shed one set.) The egg then pauses at prophase I until ovulation, when division resumes — and it is only completed after fertilisation.

Beyond the falling numbers, age exposes eggs to environmental toxins, genetic damage and free radicals. Chromosomes are damaged, the mitochondria — the egg's power stations — work poorly, and the egg becomes less able to withstand oxidative stress. The result is more chromosomally abnormal eggs and poorer embryo division, because there is less energy for it. So the chance of an abnormal embryo rises, pregnancy rates fall, and miscarriage rates climb with age.

The uterus and age

It is not only the ovaries that age. The uterus, the fallopian tubes and the vagina change too — and in the uterus those changes make conception harder and miscarriage more likely.

• Less muscle, and contractions that are less co-ordinated — which can make pushing in labour harder
• Abnormal neurotransmission to the uterine muscle, lowering the chance of pregnancy, raising the risk of miscarriage, and increasing obstetric complications such as pre-eclampsia
• The uterine lining functions abnormally, so embryo receptivity is impaired
• More chronic inflammation within the cavity

Age and a woman's wider health

Once the egg pool has fallen far and hormone levels start to shift, the effects reach well beyond fertility.

• Metabolism slows, so weight goes on easily — on average half a kilogram a year even when eating the same
• Body fat redistributes, accumulating in the abdomen — abdominal obesity
• Insulin resistance develops: blood sugar rises, lipids and cholesterol become abnormal, and blood pressure can climb
• In the long run bone thins and osteoporosis can follow — losing height, a stooped back, and fractures from even minor knocks
• Once hormones fall far enough, menopausal symptoms appear — hot flushes, sweating, poor sleep, dry skin, vaginal dryness. If they disrupt daily life or leave you irritable, they should be treated

Prevention and treatment

We cannot stop the calendar, but some things can still be prevented, corrected or treated.

• Some conditions drive the egg pool down fast, bringing menopause early: Turner syndrome, Fragile X premutation, chemotherapy, ovarian surgery, pelvic radiotherapy. Women at this kind of risk may consider fertility preservation — freezing eggs, freezing embryos (if married), or ovarian tissue cryopreservation
• If you have no plans for a child now but expect to want one later, freezing eggs is worth considering
• Live healthily: avoid alcohol, smoking and recreational drugs
• No supplement and no treatment beats your age. I will say that plainly

For those whose reserve is low and who have tried many times with their own eggs, donor eggs are one route that gets you there sooner. It may mean coming to terms with a child who does not share your genes — but you carried them, you gave birth to them, and in law you are their mother in every respect.

And do not forget the rest of your health. This is a time of transition, and problems left unattended will shorten the years you get with your child. Good luck to you all — may your baby come soon.

References

1. Na Nakhon S, Limvorapitux P, Vichinsartvichai P. Knowledge regarding factors that influence fertility in Thai reproductive-age population living in urban area: a cross-sectional study. Clin Exp Reprod Med. 2018 Mar;45(1):38-43.
2. Owen A, Carlson K, Sparzak PB. Age-related fertility decline. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024.
3. Nathan A. Reproductive aging leads to many women's health problems.
4. Female age-related fertility decline. Fertility and Sterility. 2014;101(3):633-634.
5. Knight J, Nigam Y. Anatomy and physiology of ageing 8: the reproductive system. Nursing Times. 2017;113(9):44-47.
6. Ambikairajah A, Walsh E, Cherbuin N. A review of menopause nomenclature. Reprod Health. 2022;19:29.