What is the next step for the fertilized egg after conception?

After conception, the fertilized egg, now called a zygote, undergoes a series of cell divisions as it travels down the fallopian tube toward the uterus. The key process that follows is implantation in the endometrium, the thickened lining of the uterus.

As the zygote reaches the uterus, it has developed into a blastocyst, which is essential for establishing a pregnancy. Implantation involves the blastocyst embedding itself into the endometrium, where it can receive nutrients and support from the mother’s blood supply. This attachment is critical for the embryo's subsequent development and growth.

In contrast, the other options do not align with the biological processes that follow fertilization. The zygote definitely does not move back to the ovary, as that is not part of its developmental pathway. Remaining in the fallopian tube does occur initially, but for successful pregnancy, the next necessary step is implantation. Disintegration of the zygote is also not accurate in the context of a successful conception, as it must implant to continue its development. Therefore, the successful implantation in the endometrium marks the critical next step after conception to establish a pregnancy.