Decline in Total Fertility Rate

Do you think the drop in total fertility rate (currently at 1.5 births/women) is driven by couples choosing to have less children or no children at all?

In other words, is the number of couples deciding to have children remaining the same but they are just having less of them or is the rate being driven down by couples choosing not to have children whilst other couples are having 2 or more.

EDIT thank you everyone for your responses. For further clarity what i was keen to know is whether, anecdotally of course, you think one group is contributing more to the TFR than the other.