This does not mean that the life-force [spirit] actually travels to heaven. Rather, it means that for someone who dies, any hope of future life rests with Jehovah God. His life is in God’s hands, so to speak. Only by God’s power can the spirit, or life-force, be given back so that a person may live again.
They've transformed the idea (and the words) into a metaphor. It's their way round the whole 'soul' problem. And it leaves lots of wriggle room on the question you pose too. God doesn't literally get the spirit back. He doesn't literally have to give it to make something alive. Or they'd have to explain where God fits in with the baby making process etc etc.