Can the penis penetrate the cervix. MLA Galan, Nicole. As to girth, 13cm circumference is average and should fit the vagina. Except during childbirth, the cervical os is not open and is too small to be penetrated. There is a tiny opening that runs through the center and connects the vagina to the uterus. Meaning, the build is less linear. Possible to penetrate the cervix during sex? I recommend robust vaginal weight lifting practice to restore sensation and increase articulation and strength. Learn about the causes and risk factors here, plus when someone should see a doctor.