In the Afterword to "Bloodchild" in her collection of short stories, Octavia Butler says that the story is not about slavery. As a reader, however, it's hard not to see slavery in it. "Bloodchild" is about humans who for a reason the author does not tell us have left Earth and have settled on an alien planet inhabited by a race of insectlike creatures called the Tlic. The Tlic are a parasitic species; they can only reproduce by depositing their eggs inside the bodies of other creatures. When they hatch, the larva eat their way out of the host body.
Before humans arrived, the Tlic used other native animals to gestate their young, but those animals had developed defenses against the Tlic. In order to guarantee their own safety, the humans agree to become the hosts for the Tlic and willingly allow the eggs to be inserted inside their bodies. The Tlic are very clever. They realize that if they develop friendly relations with the humans, the humans will more willingly participate in the horrible birth ritual (the hatched larvae must be removed quickly and the carcass of another animal must be prepared to put them in or they will consume the host). They also choose to impregnate only males, knowing that females are needed to reproduce more humans.
In the sense that their safety depends on their aiding in Tlic reproduction, the humans are not free. It is a kind of slavery when you are not allowed to make choices for yourself or your family.
Other than the element of slavery and the theme of pregnancy and childbirth, the reader would never know that the author of this story was an African American woman.