Do I have to do circumference measurements?

No, you do not have to do circumference measurements, but they are recommended as a useful assessment to help you set your goals and evaluate your results. These measurements are merely an estimate of body fat based on statistical data, but if an individual is losing inches, it can be assumed they are decreasing body fat. Other methods which can be used to assist in goal setting and program evaluation are body fat assessments (hydrostatic weighing, bioelectrical impedance, or skin fold measurements), using a scale for weight, using your clothes as a guide, body mass index, or waist to hip ratio.

As many people feel uncomfortable about getting their measurements done it is a useful tool in your progress.  Having your measurements done every 2-4 weeks allows you to see where you are losing it from first and what areas are not changing yet.  So just remember it is something you don't have to do but it is useful.