This is the complex process involved of a couple becoming pregnant and having a baby. The average chance is 90% in 1 year and 95% in 2 years for a normal fertile couple. The older a woman is, the reduced chances she will have of becoming pregnant and giving birth to a healthy baby. The chances start to decrease after she has reached her 35th birthday and are significantly reduced in her 40’s. This is due to not only a reduced chance of becoming pregnant but also an increased chance of having an abnormal baby, which will substantially increase her chance of miscarriage. About 1 in 3 pregnancies as defined by a positive pregnancy test will miscarry in older women.
Being either over or underweight also reduces fertility. This is outside a BMI (body mass index or ratio of weight in Kilograms divided by height in meters) of 19 to 30.