Ripley was impregnated by a Face Hugger during her cryostasis aboard the escape pod, resulting in a Xenomorph embryo developing within her.
The Impregnation Event
Following the destruction of the Nostromo, Ellen Ripley entered a hypersleep chamber aboard the escape pod, the Narcissus. It was during this period of deep cryostasis, a state of suspended animation, that she was attacked. A Face Hugger, a parasitic creature from the Xenomorph life cycle, managed to infiltrate the pod and attach itself to Ripley while she was unconscious and unaware.
The Face Hugger's method of impregnation typically involves attaching to the host's face and inserting an embryo directly into the host's body through the throat. This process ensures the successful implantation of the Xenomorph.
The Xenomorph Embryo
Upon regaining consciousness and utilizing the escape pod's barely functioning medical apparatus, Ripley conducted a scan that confirmed the presence of a Xenomorph embryo inside her. This scan further revealed that the developing organism was not a standard Xenomorph drone or warrior, but specifically an Alien Queen. This critical discovery deeply impacted Ripley's subsequent actions and the trajectory of the Alien saga.
