After pregnancy and birth, one partner may be recovering physically, adjusting to changes in their body, or dealing with pain and dryness. The other may feel pushed aside, feel unsure about when sexual initiation is welcome again, or be afraid of creating pressure. Both may be catastrophically sleep-deprived.
There is another, less obvious possibility: there may be too much touch rather than too little. If someone has been held onto, tugged, fed from, climbed on or physically needed all day, being touched by one more person in the evening may be the last thing their body wants.
That does not mean their partner has stopped being attractive. Sometimes the body has simply reached its capacity for contact. So “our sex life disappeared after the baby” can contain many completely different stories. Before trying to recreate the sexual life that existed before, it can help to understand which part of it actually changed.