The normal value of follicles for 12 days is around 14-16mm, at this time the follicle development is about to approach maturity, it is best to timely ultrasound to see the follicle development, as long as the ovary development is normal. In addition, follicles can grow 1-2mm every day, it is best to check once a day to see if the follicle growth rate is normal, as long as the follicle development is normal, there is no need to worry. If the follicle development is small or the growth rate is too slow, it may be that the estrogen secretion is too small, and it may be caused by endocrine disorders, you can go to the hospital to take a blood test for hormone six, if necessary, under the guidance of the doctor to supplement estrogen, such as estradiol valerate tablets, and you can also use the reasonable use of ovulation-promoting drugs, such as clomiphene. After the use of ovulation drugs need to be arranged in time to have intercourse, in order to improve the chances of pregnancy, ovulation drugs have certain side effects, can not take drugs.