A guide from England’s National Health Service reports: “IUDs with more copper are more than 99% effective.
وَبِٱلتَّالِي تَحْمِلُ خِلَالَ سَنَةٍ وَاحِدَةٍ أَقَلُّ مِنِ ٱمْرَأَةٍ مِنْ أَصْلِ ١٠٠ يَسْتَخْدِمْنَ ٱللَّوْلَبَ .‏