Female Fertility and Age: What Really Changes at 30, 35 and 40

“So, when's it your turn? Hurry up, the clock is ticking.” At 32 or 36, hearing that over a family meal can hurt more than you would think. Yes, female fertility and age are linked: fertility does decline over the years. But the decline is gradual, and the real numbers are much less frightening than the rumour.

Here is what the data say, age bracket by age bracket, what AMH really measures, and when it is reasonable to see a doctor without waiting.

Why does fertility decline with age?

Because a woman is born with her whole stock of eggs, which does not renew. That stock shrinks over the years, and the quality of the remaining eggs falls too. The Mayo Clinic explains that this loss speeds up as you approach forty, and that eggs from this period are less likely to lead to a pregnancy.

That is the whole meaning of the phrase “biological clock”. It does not stop suddenly at 35. It slows, gently at first, then more clearly towards forty. In some women, premature ovarian insufficiency occurs before 40, but that is the exception.

The numbers by age: chances per cycle and over a year

There are two ways of looking at this: the chance each cycle, and the cumulative chance over several months. The first impresses, the second reassures.

Per cycle, with intercourse in the fertile window, the Quebec guide Mieux vivre (INSPQ) puts the chance of fertilisation at about one in four at 20, and about one in twenty at 40.

Over one or two years, the table published by the UK institute NICE, for couples having intercourse about twice a week, gives this:

In other words, between 30 and 39, more than eight women in ten conceive within a year. The difference lies mainly in the waiting time, which lengthens. These figures are averages: they say nothing about your personal situation, which also depends on your cycles, your health and your partner's. To know what is normal month after month, read our article on how long it takes to get pregnant.

At 30, 35, 40: what changes in practice

Around 30

Fertility remains high. At this age there is no medical reason to rush if the plan is not ripe. It is, however, a good time for a pre-pregnancy consultation, which reviews vaccines, treatments and lifestyle: everything is detailed in our guide to preparing for pregnancy.

From 35

The decline becomes noticeable: pregnancies come a little less quickly, on average. The most useful change to remember is a practical one. American professional bodies (ASRM, ACOG) recommend seeing a doctor after 6 months of trying without a pregnancy, instead of 12. The UK's NHS sets this threshold at 36. The idea is not to alarm yourself, but not to lose time if a test can help.

Around 40

The ASRM estimates that at 40, fertility is about half what it was in the late twenties or early thirties. Natural pregnancies remain possible, but the wait gets longer. At this age, it is better to talk about your plans with a gynaecologist from the start, rather than after several months of waiting. Care during a pregnancy at that age is explained in our article on pregnancy after 40.

Ovarian reserve and AMH: what the test does (and does not) tell you

Ovarian reserve is the number of eggs still available in the ovaries. It is estimated in three ways: the blood test for AMH (anti-Müllerian hormone), FSH with oestradiol early in the cycle, and the count of small follicles on ultrasound.

These tests have a real use: they help the specialist predict how the ovaries will respond to stimulation, for example before IVF. But, as the American College of Obstetricians and Gynecologists (ACOG) points out, they do not reliably predict failure to conceive. A low AMH does not mean “you will not be able to have a child”. It may mean the window is a little shorter than expected, and that it is better not to put things off too long.

A man's age matters too

It is talked about less, but male fertility changes too. According to the ASRM, sperm parameters start to decline after 35, even though a man's fertility is not clearly reduced before about 50. NICE sums it up: female fertility falls with age, male fertility too, to a lesser degree.

Above all, the WHO recalls that infertility can come from the man, the woman, both, or remain unexplained. When a couple seeks help, the tests therefore involve both. The semen analysis, simple to carry out, is explained in our article on male fertility.

What weighs as much as age

Age is not the only factor, and some others can be corrected:

• Smoking: according to the Mayo Clinic, it “ages” the ovaries and depletes the reserve earlier; the ASRM notes menopause arriving 1 to 4 years earlier in women who smoke. In men, it harms sperm quality.
• Weight: marked underweight as well as marked overweight can disturb ovulation (NHS, Mayo Clinic).
• Alcohol in quantity, in women as in men.
• Untreated sexually transmitted infections, which can damage the tubes, according to the WHO.

What you put on your plate plays a more modest role: we sort evidence from received wisdom in our feature on food and fertility.

When should you see a doctor, depending on your age?

The general rule is the same everywhere: infertility is spoken of after 12 months of regular unprotected intercourse without a pregnancy (WHO). That wait shortens with age and in certain situations.

In Morocco, your first contact can be your gynaecologist, a GP or the midwife at the health centre, who will refer you if needed. The details of the tests offered to couples are in our article infertility: when to seek help and which tests.