上环为什么能避孕的原理

a cervical cap is a form of birth control or contraception it's a temporary and reusable device women can use to prevent pregnancy made of a flexible rubber。 the cervical cap is shaped like a sailor's hat it has a dome with a removal strap on top of it the brim surrounding the dome has a short side and a long side a cervical cap should be used with a substance that kills sperm called spermicide to increase its effectiveness a woman puts the cervical cap in her vagina before having sex to prevent pregnancy the dome of the cervical cap covers the cervix which prevents the sperm in the man semen from entering the uterus the spermicide applied to the cap kills the sperm that come into contact with it there are a few things to remember before using a cervical cap do not use the cervical cap？ if you have given birth within eight to ten weeks or had a miscarriage or abortion within six weeks it is easier to become pregnant using a cervical cap during these times because the cervix is larger do not use a cervical cap during the menstrual period because it can block normal drain of blood from the uterus， if you have an infection or other health condition affecting your uterus cervix or vagina， or if the cap is torn or damaged to use a cervical cap wash your hands and remove it from its container apply one quarter teaspoon of sperm aside inside the dome up to and including the brim apply an additional one half teaspoon of spermicide in the groove between the outside of the dome and the brim next choose a position for you to begin inserting the cap you can lie down with your knees bent squat with both feet on the floor or stand with one foot on a chair insert your index and middle fingers all the way into your vagina to locate your cervix so that you'll know where to place the cervical cap next squeeze the cervical cap with the dome facing away from your vagina then slide the cervical cap into your vagina with a long side of the brim entering first using one or two fingers slide the cervical cap as far into your vagina as it will go check with your fingers to make sure the cervical cap touches and completely covers your cervix you can leave the cervical cap in your vagina for up to forty eight hours before removing the cervical cap wait for six hours after the last time you had sex to remove it squat with both feet on the floor insert a finger into your vagina to find the strap covering the dome of the cervical cap gently push the dome with the tip of your finger to dimple it and break the suction attachment to your cervix then hook your finger through the strap and pull down slowly and gently after removing the cervical cap wash it with soap and water and allow it to air dry the cervical cap is most effective at preventing pregnancy in women who have never been pregnant or have never had a vaginal birth cervical caps are about 96 percent effective at preventing pregnancy if used correctly every time a woman has sex cervical caps are about ninety two percent effective with typical use which means either not always using the cap or not using it correctly every time a woman has sex。