The second poll, of 12,000 Catholics in 12 countries, showed that 78 per cent backed contraception, rising to more than 90 per cent in Argentina, Colombia, Brazil, Spain and France.
The private poll, carried out for Univision, a Spanish-language TV station in the US, found that 50 per cent said priests should be able to marry, 51 per cent favour female priests and 65 per cent said abortions should be allowed - 8 per cent in all cases, and 57 per cent in some cases.
The Pope has said he has little intention of altering rules.
Announcing the Vatican's survey last year, the coordinator of the synod, Cardinal Peter Erdo said: "We don't have a desire to reopen all the discussion on Catholic doctrine." But Archbishop Bruno Forte, the synod's Italian secretary-general, added that if respondents were unanimous "we will have to reflect, pray and [the Pope] will shed light on it".