The verb “ayant portés” is a participe passé composé (not to be confused with a participe passé, which would be “porté[e][s]”). A participe présent would be :

mères les portant pour le compte d’Israéliens …

which is synonymous with

mères qui les portent pour le compte d’Israéliens …

that is, mothers who are currently bearing them (the babies — or rather the fetuses at that point) on behalf of Israelis. The clause around the present participle is a complement of the noun “mères”; it describes an action that the mothers are currently doing or a state that the mothers are currently in. In the past tense, the sentence fragment becomes

mères les ayant portés pour le compte d’Israéliens

which is synonymous with

mères qui les ont portés pour le compte d’Israéliens

that is, mothers who in the past bore the aforementioned babies.

Note that “porté” in this context refers to a mother bearing a child (i.e. being pregnant with and giving birth to), not to carrying an infant in one’s arms.