Age and female fertility
Female fertility is affected by age. After puberty, female fertility increases and then decreases, with advanced maternal age causing an increased risk of female infertility. In humans, a woman's fertility peaks in the early and mid-20s, after which it starts to decline slowly, with a more dramatic drop at around 35. Menopause, or the cessation of menstrual periods, generally occurs in the 40s and 50s and marks the cessation of fertility, although age-related infertility can occur before then. 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."
Quantification of effect
The average age of a girl's first period (menarche) is 12 to 13 (12.5 years in the United States, 12.72 in Canada, 12.9 in the UK) but, in postmenarchal girls, about 80% of the cycles are anovulatory in the first year after menarche, 50% in the third and 10% in the sixth year. A woman's fertility peaks in her early and mid-20s, after which it starts to decline, with this decline being accelerated after age 35. However, the exact estimates of the chances of a woman to conceive after a certain age are not clear, with research giving differing results. The chances of a couple to successfully conceive at an advanced age depend on many factors, such as the general health of a woman and the fertility of the male partner.
According to the National Institute for Health and Clinical Excellence, for women aged 35, about 94 out of every 100 who have regular unprotected sexual intercourse will get pregnant within 3 years of trying. For women aged 38, however, only 77 out of every 100 will do so.
According to Henri Leridon, PhD, an epidemiologist with the French Institute of Health and Medical Research, of women trying to get pregnant, without using fertility drugs or in vitro fertilization
- At age 30
- 75% will have a conception ending in a live birth within one year
- 91% will have a conception ending in a live birth within four years.
- At age 35
- 66% will have a conception ending in a live birth within one year
- 84% will have a conception ending in a live birth within four years.
- At age 40
- 44% will have a conception ending in a live birth within one year
- 64% will have a conception ending in a live birth within four years.
According to a study done on a sample of 782 healthy European couples ages 19–39, fertility starts declining after age 27 and drops at a somewhat greater rate after age 35. The women were divided into four age groups: 19–26, 27–29, 30–34 and 35–39. Statistical analysis showed that the women in the 27–29 age group had significantly less chance on average of becoming pregnant than did the 19– to 26-year-olds. Pregnancy rates did not change notably between the 27–29 age group and the 30–34 age group, but dropped sharply for women over 35. The age of the male partner had a significant impact on female fertility among the women who had reached their mid-30s, but not among the younger women. However, experts said the new study was too small and there were too many variables which were too difficult to sort out, for a clear conclusion to be drawn. Some experts suggested that the main change in fertility in the older women was the fact that it took them longer to conceive, not necessary that they were significantly more unlikely to eventually succeed. David Dunson, a biostatistician at the U.S. National Institute of Environmental Health Sciences, said that: "Although we noted a decline in female fertility in the late 20s, what we found was a decrease in the probability of becoming pregnant per menstrual cycle, not in the probability of eventually achieving a pregnancy."
A French study found no difference between the fertility rate of women under 25 and those ages 26–30, after which fertility started to decrease. Estimating the "fertility of a woman" is quite difficult because of the male factor (quality of sperm). This French study looked at 2,193 women who were using artificial insemination because their husbands were azoospermic. The cumulative success rates after 12 cycles of insemination were 73% for women under age 25, 74% in women ages 26–30, 61% for ages 31–35, and 54% in the over 35 age group. (Note that the study is from 1982; artificial insemination techniques and success rates have evolved greatly since then.)
In Hungary, a study by the Központi Statisztikai Hivatal (Central Statistics Office) estimated that 7%–12% of Hungarian women younger than 30 were infertile; 13%–22% of women age 35 were infertile; and 24%–46% of women age 40 were infertile.
The below is a table containing estimates of the percentage of women who, if starting to conceive at a certain age, will fail to obtain a live birth. Note that while for the young ages researchers tend to agree, for older ages there is discrepancy.
|Age of woman when she starts to try to conceive||% who will have no live birth according to Vincent (1950)||% who will have no live birth according to Henry (1953), England||% who will have no live birth according to Henry (1953), Norway||% who will have no live birth according to Pittenger (1973)||% who will have no live birth according to Leridon (1977)||% who will have no live birth according to Trussell-Wilson (1985)||% who will have no live birth according to Menken-Larsen (1986)|
As observed in the table above, there isn't much agreement about the ability of women in their forties to have a live birth.
In terms of ovarian reserve, a typical woman has 12% of her reserve at age 30 and has only 3% at age 40. 81% of variation in ovarian reserve is due to age alone, making age the most important factor in female infertility.
The most common methods of checking the status of the ovarian reserve is to perform a blood test on day 3 of the menstrual cycle to measure serum FSH level, alternatively a blood test to measure the serum AMH level can give similar information. Transvaginal ultrasound can also be used to “count the number of follicles” and this procedure is called Antral Follicle Count.
A study of a population of French women from 1670 and 1789 shows that those who married at age 20–24 had 7.0 children on average and 3.7% remained childless. Women who married at age 25–29 years had a mean of 5.7 children and 5.0% remained childless. Women who married at 30–34 years had a mean of 4.0 children and 8.2% remained childless.
In 1957, a study was done on a large population that never used birth control. The investigators measured the relationship between the age of the female partner and fertility. (Infertility rates today are believed to be higher in the general population than for the population in this study from the 1950s.)
This 1957 study found that:
- By age 30, 7% of couples were infertile
- By age 35, 11% of couples were infertile
- By age 40, 33% of couples were infertile
- At age 45, 87% of couples were infertile
The inverse correlation between age and female fertility in later reproductive life is argued to motivate family planning well before having reached 35 years of age. Mapping of a woman's ovarian reserve, follicular dynamics and associated biomarkers can give an individual prognosis about future chances of pregnancy, facilitating an informed choice of when to have children.
Most in vitro fertilization (IVF) centers will attempt IVF using the female partner's own eggs until about age 43–45. Michael Fox, M.D., a reproductive endocrinologist in Jacksonville, Florida states that, in regard to assisted reproduction treatment, "in general our approach to treatment of patients over age 35 is vastly more aggressive than in younger patients."
Elite egg donor agencies that advertise in places such as Ivy League student newspapers offering up to $20,000 or even $50,000 for donor eggs seek donors under the age of 29.
The issues of age need to be taken up with a qualified fertility specialist such as a reproductive endocrinologist.
A review in 2012 came to the result that therapeutic interventions to halt or reverse the process of reproductive ageing in women is limited, despite recent reports of the potential existence of stem cells which may be used to restore the ovarian reserve.
A study commissioned by RESOLVE, a non-profit patient advocacy organization, states that both three out of four men and three out of four women overestimate by five years the age of the onset of the rapid decline which is at 35 instead of 40 as most people commonly believe. The American Society for Reproductive Medicine (ASRM) states, "...women in their 20's to early 30's are most likely to conceive."
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