Natural fertility declines as women get older. The chance of conceiving per month drops from about 20 – 25 % at aged 30 to about 5 % at 40 and after age 40 this decline accelerates again. Rates of miscarriage can be high because of chromosomal defects in the oocytes. Blood tests like FSH and AMH and ultrasound of the ovaries give us a good indication of how likely a pregnancy is.