It is a fact that women’s fertility decreases as they age. But the general description of the decline in fertility after age 35 as a ‘cliff’ is more disturbing than factual.
If you want children, understanding the biology of fertility is important. This can help those who have timing choices to decide when to start trying for a baby.
And for those who don’t have a choice when it comes to timing, knowing the options can help make the best decisions possible.
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Female age, egg count and quality
A little girl is born with about a million eggs in her tiny ovaries, but by the time she reaches puberty there are only about 300,000 eggs left. This is a normal physiological process called atresia.
Of the eggs that remain when a woman gets her period, only 300-400 will mature and be released during the reproductive years at ovulation. When a woman reaches menopause, there are no longer any functioning eggs in her ovaries.
While women in their mid to late 40s sometimes have “miracle babies,” the chances of pregnancy in the 5-10 years leading up to menopause are minimal.
As the woman ages, the quality of the egg cell also decreases. It is estimated that around 20 percent of all human egg cells are “aneuploid,” meaning they have the wrong number of chromosomes. This percentage increases as the women get older.
When an aneuploid egg cell is fertilized by a sperm, the result is an aneuploid embryo – which in most cases fails to develop or ends in early miscarriage.
What does this mean for the chance of having a baby at different ages?
A woman’s most fertile years are between her late teens and late twenties. Around the age of 30, fertility slowly begins to decline and from the mid-30s the decline accelerates.
But the likelihood of pregnancy after age 35 gradually decreases and resembles more of a slope than a cliff, at least until age 40.
A large study that followed women trying to have a baby found that the chance of pregnancy at 12 months was 87 percent for women aged 30 to 31. This fell to 76 percent for those aged 36 to 37 and to 54 percent for those aged 40 to 41.
By the age of 41, most women trying to have a baby will be pregnant by up to 12 months. But the proportion not achieving pregnancy increases with age, and the decline in probability is more pronounced after age 35.
Unfortunately, since the number of chromosomally abnormal (aneuploid) eggs increases with age, the risk of miscarriage increases as a woman ages. For women in their early to mid-30s, the risk of miscarriage is about one in ten. In women aged 40 to 44, it increases to about one in three.
What about male age and fertility?
While it happens later in life than in women, men’s age also affects their chances of pregnancy.
Sperm quality and fertility decline around age 45, and pregnancies conceived by men age 45 and older are nearly 50 percent more likely to miscarry than pregnancies conceived by men age 25 were conceived before the age of 29.
IVF is not a good plan B
Unfortunately, IVF cannot improve egg quality, and the woman’s age is the most important factor in IVF success. Data from Victoria shows that after three completed IVF cycles, 61 percent of women aged 34 to 35 when they started treatment were having a baby.
The chance of having a baby after three cycles was 50 percent at age 36-37 and 38 percent at age 38-39. But by the age of 40-41, only 25 percent of women have had a baby after three IVF cycles.
The chance of IVF success is also affected by the age of the male partner. Studies show that the live birth rate is lower in couples where the male partner is 45 years of age or older than in couples where the male partner is younger.
What are the options?
Life circumstances, including not having a partner willing to commit to parenting, can prevent people from having children in their most fertile years.
Here are some options if you’re concerned about how age might affect your chances of having a baby:
- Going Solo: If you’re single, you may consider joining the growing group of women who are using donor sperm to become ‘choice solo moms’. The safest option for you and your baby is to find a donor through a fertility clinic.
- Freezing eggs for later: While this seems like an attractive option, it is costly and there is no guarantee of a baby in the future. To help you decide if this is the right option for you, here are some egg freezing facts.
- with IVF: If you’re 35 or older and have been trying to have a baby for at least six months, see your GP for advice and basic fertility testing. Depending on the test results, your GP may refer you to a fertility specialist. If you need IVF, sooner is better than later as age affects the chances of IVF success.
- Using Donor Eggs: The chance of having a baby with IVF after the age of 40 is negligible unless you use eggs donated by a younger woman. Studies show that women who use donor eggs are five times more likely to have a baby after the age of 40 than women who use their own eggs.
Finally, a word of caution. Ovarian reserve tests are often advertised as a way for women to find out their fertility and chances of conceiving.
The so-called “egg timer” test measures blood levels of anti-Müllerian hormone (AMH), a hormone produced by reproductive tissues. The thought is that the more eggs there are, the more AMH there will be, so it’s marketed as a sort of “egg counting.”
However, research shows that the test is not a reliable test of a woman’s fertility. On average, women of the same age have the same monthly chance of conceiving, regardless of their AMH level.
This article first appeared in The conversation.
Karin Hammarberg is one Global and Women’s Health Unit Senior Research Fellow at Monash University School of Public Health and Preventive Medicine.
https://7news.com.au/lifestyle/health-wellbeing/women-are-often-told-their-fertility-falls-off-a-cliff-at-35-but-is-that-right-c-9038361 Women are often told that their fertility “falls off a cliff” at 35, but is that true?