Regulating the population of reproductively capable biont sentients, or of neumann-capable vecs and ais. Because such sophonts have the tendency, if unregulated, to spread throughout the universe in the form of "pink goo" (for bionts) or analogous kinds of "goo", various birth control techniques are used by different cultures in the civilized galaxy.
A popular option involves nano or genegineering to ensure that the only way that two or more people can conceive a child is if all parties actively want a pregnancy to occur. This may require taking a "deactivator" drug to turn off the birth control nano, or having conscious control over ones fertility. In other words the parents have to turn their fertility on in order to conceive. Accidental pregnancy (happy or otherwise) in this situation is impossible.
In more regulated polities, the tech is remotely controlled by the ruling AI. The sophont doesn't get pregnant or cause pregnancies unless the AI decides they should. Or after a certain number of offspring the system permanently locks down the person's fertility.
This may especially apply to those who use technology to increase their lifespan. They can live forever but then they cannot have children, or in some cases one per century is permissible.