The structure in which a fertilized egg grows and develops into a baby is called the uterus.

Here's a breakdown:

* Fertilization: A sperm cell fertilizes an egg cell, creating a zygote.

* Implantation: The zygote travels down the fallopian tube and implants itself in the lining of the uterus.

* Development: The fertilized egg, now called an embryo, grows and develops within the uterus, receiving nourishment and protection from the mother's body.

* Birth: After approximately 40 weeks, the baby is born through the cervix and vagina.