Sperm may lose their ability to navigate in microgravity, raising new questions about whether human reproduction is possible in space.

WASHINGTON — For the first time, scientists have used human cells to make structures that mimic the earliest stages of development, which they say will pave the way for more research without running ...

The first steps of human development—those that occur within the first few weeks of pregnancy—remain mysterious in many ways. Within a week of fertilization, human embryos form a blastocyst, which ...