Calendar, temperature chart marked in red, red pen and thermometer

Ovulation

Your time of ovulation is one of the most important things to understand because ovulation is a key factor in getting pregnant.
Just before ovulation, basal body temperature usually drops, with a sharp increase right after ovulation. 
If you're trying to get pregnant, it's essential to find out when you're likely to ovulate and are most fertile.
If you do need to undergo fertility treatment, you may be in it for the long haul; it can take months or years to determine a cause or appropriate treatment, which is why older couples are advised to start fertility investigations earlier.