Fetal head detection and approximation from ultrasound image is an important method in obstetric and gynaecology. In this research, we propose a modification of an efficient algorithm to detect an ellipse shape in an image. Our proposed method is using an efficient way to approximate an ellipse based on its minor axis. By enumerating every possible minor axis from a pairs of pixels, other ellipse parameter can be estimated. For verifying the ellipse approximation result, a voting mechanism is conducted to vote the most appropriate set of parameters for an ellipse. Instead of using every edge pixels in the image, we randomize the pixels to gain speed improvement. We test the algorithm using two different data. The first one is real ultrasound image and the second one is synthetic image which has been populated with salt noise. The ultrasound image is cleaned from speckle noise using Speckle Reducing Anisotropic Diffusion (SRAD) algorithm. The experiment gives satisfying result in both of synthetic and real images.