Although the sex of your baby was determined at the moment of fertilization, it will not yet be apparent whether the embryo is male or female.

At this stage of development, the external genitalia have exactly the same appearance (almost nonexistent). In a girl, no uterus or tubes have formed internally. The ovary in a female embryo and testes in a male embryo are currently just ridges of tissue, without any of the characteristics of either reproductive organ.

Incredibly, your baby's heart has already developed, with four chambers beating at about 160 beats per minute. The common tube leaving the heart has divided into the two main blood vessels: the aorta takes your baby's oxygen-carrying blood to his body and the pulmonary trunk takes his blood to the lungs. Valves within the heart ensure that the blood only travels one way and all of the major blood vessels are now established.

Your baby's eyes appear open because the eyelids have just started to appear and have yet to fuse. In reality, they won't properly open until week 26. Pigment is just starting to accumulate within the retina of the eye. The developing lens is supplied by a single blood vessel in the optic nerve, which will later disappear.