Only high ranking men - such as Commanders - are allowed to have a Handmaid assigned to them.

Are all commanders wives infertile?

Wives are usually married to high ranking men in Gilead, such as Commanders, Angels and Eyes. ... It is implied that some Wives are capable of bearing children, but most are older women and thus have difficulty conceiving (or their husbands are infertile), which is also hampered by widespread infertility.

Why are Econowives not handmaids?

They are married women whose husbands rank lower than Commander or Professional, such as Guardians or Economen. Their husbands cannot be allocated a Handmaid if they prove infertile, nor can a Martha help around the house; thus Econowives must bear children and do domestic work.