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If you're a woman who's hoping to get pregnant, the age of 35 might weigh heavily on your mind. That's because, for many years, it's been understood to be the point where pregnancy becomes much harder.
One of the largest studies on age-related fertility decline took place in Denmark in 2013. A sample of 2,820 Danish women, who had unprotected intercourse twice a week, were assessed.
While it's true that the likelihood of falling pregnant within your first three months of trying declines after age 35, this reduction is said to occur on a continuum rather than age 35 representing a cliff edge.
Overall, women in their late thirties experience more difficulties conceiving, and there is a higher risk associated with both the pregnancy and the delivery.
It was found that peak fecundity - the ability to produce offspring - was reached in women at around 30 years of age. It occurred slightly earlier in women who hadn't already had a live birth compared to those who had.
Within 12 menstrual cycles, conception occurred at a rate of 84% of those aged 25-29, 88% of those aged 30-34, and 73% of those aged 35-40.
A pregnancy where the mother-to-be is 35 or older is medically referred to as a "geriatric pregnancy" or she's described as having an "advanced maternal age."
The results were observed in women whose partners were younger than them. If their partner was 40, the result was reduced to 43%. The study followed women who only used natural methods of conceiving.
In a separate study, it was found more than half of women who were in their late thirties and hadn't become pregnant within a year of trying, had become so after two years.
These percentages increase with the number of egg retrievals that take place, as they represent the live births resulting from one retrieval.
The clinical definition of infertility is being unable to get pregnant spontaneously, after a year of regular, unprotected intercourse.
Most women who try to get pregnant at age 40 will face real difficulty, despite the fact that the average age at which women experience menopause is quite far off—around age 51/52.
Spontaneous conception in women declared infertile, without medical assistance, was examined in an academic review in 2020.
After one year, at 35 years old, the chance of conceiving was 29%, where it remained until age 38. At 39, 25% of women were successful; while at 40, the number stood at 22%; at 41, 18%; and at 42, 15%.
The rate of decline in egg quality and quantity speeds up significantly when a woman is in her thirties, making it harder to conceive.
Fecundability for couples at 40 was approximately half of what it was at age 30. Other factors including intercourse frequency and timing; as well as using nonhormonal birth control as the last method; when taken together, had small effects on offsetting the decline in fecundability.
"Is 29% at 35 that different from 22% at 40? Probably most people would not find much difference in those numbers," he explains, as a critic of the focus on age 35 and conception.
Spencer McClelland, an obstetrician-gynecologist at the Denver Health Hospital, US, says: "There is a statistically significant change in the rate of decline at 38."
Overall, a woman's fertility is as individual as she is. For now, what we know is—it's complicated.
Sources: (BBC) (Slate) (CDC) (Europe PMC) (WHO) (Academic) (The BMJ)
See also: Could it be perimenopause? Here's what you should know
What many of these numbers, when taken together, suggest is that while fertility might begin to decline more in the late thirties, 40 is a turning point.
The use of Assisted Reproductive Techniques (ART) offers hope to many who are trying to conceive in their mid to late thirties and over.
In those under 35, the rate is 54.1%. The rate drops to 26.9% for those aged 38 to 40, and to 9.3% for those aged over 40.
Data from 2020 showed that a sizable number (40.6%) of women aged 35-37, who underwent ART egg retrieval in the US, had a live birth.
With six cycles of in vitro fertilization (IVF) 68% of women who were under 40 years of age and used their own eggs, had a live birth.
However, when the age of the women who'd had six rounds of IVF increased to those between 40 and 42, the success rate was less than half of that 68%.
The risk of miscarriage also increases with age. At age 35, it stands at a rate of 20%, double what it is for women in their early twenties.
In one large Danish study, it was observed that when the age of the expectant mother increased to 42, more than half of pregnancies (55%) resulted in a stillbirth.
The risks involved are more complicated than just being age-related. Lifestyle factors including obesity, smoking, and alcohol consumption also impact the risks associated with pregnancy, as well as the quality of the remaining eggs. If a woman's partner is over 40 years old, her risk of miscarriage also increases.
Recently, there's been a spike in what people are dubbing "Ozempic babies," with certain people who take the GLP-1 medication unexpectedly falling pregnant. Age-related data is not yet available but again, this demonstrates there is much that we don't know about women's fertility.
However, the rate of decline is not something that occurs at the exact same rate across the board, as it differs from person to person.
Infertility in women increases naturally with age. This is because a woman's egg count falls as she gets older, and the quality of the eggs remaining is lower.
Intrigued? Click on to learn what we really know about the topic of women's fertility.
Is women's fertility more complicated than we've been led to believe?
We're told it's almost impossible after 35, but is that actually true?
HEALTH Woman
Women's fertility is complicated. There are a lot of misconceptions out there and blanket statements, but not necessarily a lot of research to back them all up. From a young age, we're told fertility falls off a cliff at 35. But is that actually true? While modern interventions can attempt to assist where people encounter difficulties conceiving, there is still much we're only just beginning to understand about women's fertility: something the recent "Ozempic babies" trend is bringing attention to.
Intrigued? Click on to learn what we really know about the topic of women's fertility.