When a baby is born, she is born with the entire number of follicles, or eggs that are there for her lifetime. So when she matures, they mature into eggs and they get released after the menarche has happened. So a follicular study scans are done to see if these follicles is it increasing in size, is it rupturing to release the egg, whether they are maturing, too release the egg or not. So follicular study scans are ultrasound scans usually done transvaginally, but done trans abdominally also, these are done to detect the number of follicles that are there for that month. The number of follicles that are increasing in size, progressively, and the follicles that are ruptured one or two and the egg release that are seen. So these are the methods to see if the follicles are increasing in size an if the ovulation is happening to see if the signs are there. So usually a 9th day scan is done to see if the follicles are growing and if enough are there. But when you are worried about fertility patients when enough follicles are not there at all, you may do a day 3, day 4 scan to check baseline follicles that have come for that month. So basically you can start day 3, day 4 or day 9 and then do it in alternate days to see if the follicles are maturing in size and number and then later on to see the signs of ovulation. When a person is on fertility treatment, that means the person is on a lot of hormonal tablets. So it is basically to coincide with the follicular scans every month rather than wasting the cycle just giving hormones to the patient, so coinciding with the follicular scans to see when the ovulation is happening . Because after ovulation the egg stays back only for 12 to 24 hours. So appropriate measures have to be taken for fertilization.