Try “commensalism” – the inbetween stage between parasitism and mutualistic symbiosis. The commensal organism lives inside the host but does not injure it, other than perhaps diverting some nutrients from the host’s ingestion of foodstuffs.
To me it all depends on how you interpret the definitions. There was a time, within living memory, when the potential for survival in old age depended on having at least one child willing to provide for you when you became too enfeebled to completely care for yourself. Hence pregnancy could easily be seen as a time-binding mutualism: divert your resources to the embryo now, and it will grow into an adult which will provide care for you in the future.