Is the word "haram" – said with the intention of "it is forbidden for me to get pregnant again" – considered an oath that requires expiation after pregnancy?

The stated formula "haram" without mentioning what is sworn upon does not constitute a binding oath, because an oath requires mentioning that which is sworn upon. Prohibiting what is lawful with this formula does not obligate the one who swore to abandon it; rather, he must seek forgiveness for prohibiting what Allah has made lawful. Therefore, the questioner must seek forgiveness and is not required to offer expiation because the oath was not binding.