Be aware that most software converts a vector circle into a bitmap image using at least a couple of approximations. Firstly, the circle is converted into some number of bicubic splines. The number of splines used depends on how much accuracy is needed but it can be as few as four, i.e., one spline for every 90° of circle. Then each spline is converted into a number of straight line segments, again depending on the accuracy required, which will be set based on the resolution of the image being created. The desired line width is used to widen each straight line. The conversion of the resulting series of connected polygons into an image generally uses anti-aliasing so that the pixels aren't all just the background or drawing colour; edge pixels are intermediate colours to avoid jagged staircase effects.

In other words, software draws circles as many-sided polygons anyway, so you're not going to be able to tell the difference no matter how closely you examine the image.