The relationship between age and female fertility is popularly referred to as a woman’s “biological clock”; when a woman reaches an age where fertility is commonly understood to drop, it can be said that her “biological clock is ticking.

All women are born with a finite number of eggs, typically up to one million. By the time puberty is reached the number of eggs is reduced to approximately 500,000. From puberty (around age 12) to menopause (around age 51+) there is a progressive depletion of egg number and quality in the ovaries, and therefore a decrease in ovarian reserve and reproductive potential. The rate of loss of oocytes within the ovary is genetically predetermined. Some women will experience a significant decline in the quantity of their oocytes in their forties, while others may experience this much earlier. 

Fertility peaks in most women in their 20s, and gradually begins to decline in the late 20s. At around age 35, fertility starts to decline at a much more rapid pace. As you age and come closer to menopause, your ovaries respond less well to the hormones that are responsible for helping the eggs ovulate. Research has found that in any given month your chances of getting pregnant at: 

Age 20 – 35 is about 25%

Age 35 – 39 is about 18%

Age 40 is about 5%

Pregnancy in your 20’s

Most women in their 20’s have a very good change of falling pregnant as a result of having a relatively greater number of eggs in their ovaries. In addition, a larger percentage of the eggs are genetically normal, leading to a great chance of fertilisation and a successful pregnancy. As women age they have fewer eggs left while the percentage of genetically normal eggs remaining decreases. 

The pregnancy rate per month of a woman in her 20’s is about 25%. While it is normally recommended to see a fertility specialist after unsuccessfully trying to fall pregnant for over 12 months, at Medfem Fertility Clinic we encourage people to book a consultation as soon as they feel in any way worried about their fertility. 

The chances of a genetic abnormality like Down syndrome are about 1/1200 for a woman in her 20’s. 

Pregnancy in your early 30’s

Women in their early 30’s will experience a decline in their fertility such that the fertility rate per month will be lower than in the 20’s.  Again, while it is normally recommended to see a fertility specialist after unsuccessfully trying to fall pregnant for over 12 months, at Medfem Fertility Clinic we encourage people to book a consultation as soon as they feel in any way worried about their fertility. The risk of miscarriage at 30 is about 20%, and the risk of genetic abnormalities is slight higher than for women in their 20’s. 

Pregnancy in your late 30’s

Women in their late 30’s face a notable decline in their fertility rate, to a level of about 18% a month. While it is normally recommended to see a fertility specialist after unsuccessfully trying to fall pregnant for 6 months, at Medfem Fertility Clinic we encourage people to book a consultation as soon as they feel in any way worried about their fertility.

The pregnancy risk for women in their late 30’s is much higher than for younger women, evidenced by an increase in the miscarriage rate and a higher rate of genetic abnormalities. At 35+ the miscarriage rate is roughly 25% and the risk of Downs syndrome becomes about 1/350. 

Pregnancy in your early 40’s

There is a very sharp decline in a woman’s ability to fall pregnant once over the age of 40. The fertility rate per month is only about 5% per month and even with IVF the pregnancy rate is only about 10% per try. This is due to the greatly reduced number of genetically normal eggs remaining in the ovaries of a woman over forty. The pregnancy risk for women in their early 40’s is again much higher, with miscarriage rates at roughly 35%, and the risk of Downs syndrome about 1/38. For this reason many women in their 40’s choose to use an egg donor to become pregnant, with success rates of about 80% per cycle. In these cases as the eggs used are from much younger women, the rate of miscarriage and genetic abnormalities are also those of the younger woman. 

Pregnancy in your late 40’s

Pregnancy for women over 45 is a very difficult proposition. Women over 45 have a less than 1% chance of falling pregnant with their own eggs. This is primarily due to the fact that the majority of their remaining eggs are genetically abnormal. The vast majority of women in this age bracket choose to use donor eggs in order to fall pregnant. 

A woman aged 45+ who falls pregnant with her own eggs faces a pregnancy risk of 50% and higher. The incidence of a genetically normal pregnancy is 1 in 12. There is also an increased risk to the health of the woman due to higher blood pressure, heart disease and diabetes. 

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