Age and female fertility

Female fertility is affected by age. Age is thus a major fertility factor for women. Menarche, the first menstrual period, usually occurs around 12–13, although it may happen earlier or later, depending on each girl. After puberty, female fertility increases and then decreases, with advanced maternal age causing an increased risk of female infertility. Female fertility is affected by age. Age is thus a major fertility factor for women. Menarche, the first menstrual period, usually occurs around 12–13, although it may happen earlier or later, depending on each girl. After puberty, female fertility increases and then decreases, with advanced maternal age causing an increased risk of female infertility. A woman's fertility peaks in the early and mid-20s, after which it starts to decline slowly. While many sources suggest a more dramatic drop at around 35, this is unclear since studies are still cited from the nineteenth century and earlier. One 2004 study of European women found fertility of the 27–34 and the 35–39 groups had only a four-percent difference. At age 45, a woman starting to try to conceive will have no live birth in 50–80 percent of cases. 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 sometimes referred to as a woman's 'biological clock.' The average age of a young woman'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. However, the exact estimates of the chances of a woman to conceive after a certain age are not clear, and are subject to debate. According to the National Institute for Health and Clinical Excellence (NICE) over 80 out of every 100 women aged under 40 who have regular unprotected sexual intercourse will get pregnant within 1 year of trying. In the second year the percentage rises to over 90%. According to a 2004 study by 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. 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 significantly for the 35–39 age group. 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.