Why can an embryo’s sex not usually be identified by external anatomy during the first eight weeks?

During the first eight weeks of development, an embryo is in what is commonly referred to as an "indifferent stage". During this period, the external genitalia of all embryos appear identical, consisting of three simple protuberances. Because these structures have not yet undergone the differentiation that leads to male or female characteristics, the sex of the embryo cannot be identified by external anatomy.12

It is only after this initial phase that differentiation begins, driven by the development of the gonads and the subsequent influence of hormones. In the male, these early structures eventually develop into the penis and scrotum, while in the female, they develop into the clitoris and other components of the vulva. Prior to these changes, the genetic sex of the embryo can only be determined by examining the chromosomes within its cells.324