How are Fertility and Age Related?
It is no surprise to most women that fertility and age are closely related, but not many know in what ways.
A woman’s fertility mainly depends on her ovarian reserve, which is the capacity of her ovaries to provide viable eggs that can be released on ovulation, fertilized by sperm, and develop into a healthy pregnancy.
However, like all other cells in the body, women’s eggs age, resulting in a natural decline in their count and quality.
Egg Count
This term refers to the number of eggs in the ovaries. Women are born with a lifetime supply of eggs, and the body cannot produce more throughout their life.
The decline of female egg count by age occurs in the following pattern through various life stages:
• At birth, ovaries contain between 1-2 million egg cells, which will degrade until puberty.
• At puberty, girls have about 350,000-500,000 eggs in the ovaries.
• Mensuration. From puberty until menopause, up to about 1,000 eggs will be recruited to be matured during each menstrual cycle, in which one egg will be released on ovulation.
• At menopause, the ovarian reserve is down to zero, and women no longer ovulate nor conceive.
Egg Quality
Over time, there are chromosomal (DNA) changes in the eggs due to sicknesses, fevers, toxins, and other factors. An egg with such abnormalities is not viable and will cause a series of complications if it is released on ovulation day, including not being fertilized, failing to implant in the uterine wall, or leading to a miscarriage or birth defects in the fetus.
Because egg quality cannot be improved, abnormal eggs accumulate over time, resulting in a higher percentage of abnormal eggs among older women, as shown in this egg quality-age chart:
• Usually before 30, women have mostly normal eggs with a few abnormal ones.
• Between 30 and 40, the percentage of abnormal eggs starts to increase while normal egg count decreases.
• After 40, women have mostly abnormal with very few normal ones.
Fertility Rates in Your 20s
• Before the age of 30, women have a 25% chance of getting pregnant in a given menstrual cycle.
• About 96% of those younger than 25 and 86% of those approaching 30 will get pregnant within a year of trying.
• Miscarriage rates are low, around 10%.
Fertility Rates in Your 30s
The early 30s
Chances of getting pregnant for women younger than 35 are still high.
• Every month, there is a 20% chance of conceiving for women in that age group.
• Over a 12-month period, it is estimated that 86% of women 30 to 34 years old will get pregnant.
The mid to late 30s
• At this age, a woman’s chances to get pregnant within a given cycle drop to 15%.
• The risk of miscarriage increases to 20-25%. The risk of genetic conditions, such as Down syndrome, increases as well. (For comparison, at 25, there is a 1 in 1,200 risk. At 35, it increases to 1 in 350 pregnancies.)
• However, 78% of women in their mid- and late 30s conceive within a year and go on to have healthy pregnancies.
Fertility Rates in Your 40s
The early 40s
A natural conception is harder, and it might take longer. However, it is still possible for women after 40.
• Women in this age range have a 5% chance of getting pregnant naturally every cycle.
• Their odds of pregnancy within a year are 40%, less than half of what it was in their 20s.
• Miscarriage rates are significantly higher, too, about 34%.
• More women have to rely on assisted reproductive technologies (ARTs), such as IVF, to achieve pregnancy.
Mid-40s
• At this age, the odds of getting pregnant within a year are only 1-3%.
• Most pregnancies are achieved with the help of donor eggs and ARTs.
• Miscarriage rates increase to 53%, and the risk of Down syndrome is very high, 1 in 10 pregnancies.
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Key Takeaways
The age-related fertility decline is an inevitable part of being a woman. Her ability to have children depends on whether her ovaries have enough good eggs that can progress into a healthy pregnancy. However, eggs, like other body cells, degrade over time, causing a decline in fertility rates by age. For women in their 20s, these natural processes are barely noticeable; in fact, 96% of women below 25 succeed in getting pregnant within a year. Those in their 30s start noticing first signs of fertility limitations, but still have a good chance of conceiving. Entering 40, however, creates many reproductive challenges as it becomes almost impossible for women to get pregnant naturally. Understanding the relationship between fertility and age is, therefore, necessary for proper family planning and fertility preservation.
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