One out of three women over the age of 35 will not conceive after one year of trying to conceive (TTC). While that statistic may sound about right to most people, it may not necessarily be true in the present day. That is because the statistic is actually the result of a scientific study performed 300 years ago.

In the 1700s, French scientists tried to correlate a woman’s age with her chances of becoming pregnant. These researchers poured over church birth records to calculate the likelihood of pregnancy after various ages. The results from this centuries-old research may not correlate to modern women as scientists performed this study before the advent of modern healthcare, technically advanced prenatal screening, nutritional information, and even electricity.

However, the French study did not have to consider the one wildcard that makes it difficult, if not impossible, for modern researchers to calculate fertility-to-age ratios today – birth control.

Despite the statistical obstacle that birth control poses to calculating fertility rates, some modern researchers have tried to estimate how likely a woman will become pregnant at various stages of her life. A 2004 paper published by David Dunson in Oxford Journals found 86 percent of women aged 27 – 34 and 82 percent of women between the ages of 35 and 39 became pregnant within one year of trying to conceive. While it is hard for scientists to determine actual numbers because of increased IVF and other fertility treatments among older women, it does seem that spontaneous pregnancies decline rapidly after the age of 40.

One of the largest problems with the 300-year old study is that it does not consider the number of women who were trying to get pregnant or trying to avoid having another baby. Many of the older women may have refused intercourse to prevent another pregnancy. Furthermore, the French statistics do not account for the possible decrease in the number of times an older couple may have intercourse.

Are the risks for chromosomal abnormalities overstated too?
Perhaps. In an interview by BBC News Magazine, David James of the UK's National Institute for Health and Care Excellence says the chances for chromosomal abnormalities is one in 400 at the age of 30, and one in 60-70 at age 40.

New research continues to shed light on fertility as a woman ages as well as her associated risks with pregnancy. Older women should discuss their fertility options with their physician or a fertility specialist.


  • David B. Dunson, Bernardo Colombo, and Donna D. Baird. "Changes with age in the level and duration of fertility in the menstrual cycle." Hum. Reprod. 2002 17: 1399-1403.
  • Barnes, Hannah. "The 300-year-old fertility statistics still in use today." BBC News. 17 Sept 2013. Web. 2 Oct 2013.