A follicle that has matured for several days before it is ovulated is still fertile, so don’t be nervous. Generally follicles are considered mature after they reach 18 millimeters. Some women may ovulate at 18 millimeters, but others may not ovulate until 25 millimeters or more. As long as the ovaries are able to ovulate, they are capable of conceiving. If you are planning to get pregnant and usually have a regular menstrual cycle, you should go to the hospital for ultrasound to monitor your follicles from the 10th day of your period. After the follicles are mature, you can have intercourse every other day and continue to do ultrasound monitoring until ovulation, which will increase the chances of pregnancy. At 10 days after ovulation, you can take a blood test for human chorionic gonadotropin or test your urine with a pregnancy test about two weeks after ovulation to determine if you are pregnant.