A cerclage procedure is performed for which of the following conditions?

The cerclage procedure is specifically designed to address an incompetent cervix, which occurs when the cervix is unable to support a pregnancy due to structural weaknesses. In this condition, the cervix may begin to dilate prematurely, leading to a risk of miscarriage or premature birth. During a cerclage, a stitch is placed around the cervix to keep it closed and provide support during pregnancy, preventing potential complications associated with cervical insufficiency.

In contrast, the other conditions listed do not involve the structural integrity of the cervix in the same way. For example, a Bartholin's cyst relates to a blockage in the glands near the vaginal opening, requiring different treatment modalities. Ectopic pregnancy refers to the implantation of a fertilized egg outside the uterus, usually in a fallopian tube, which is a surgical emergency but not treated with cerclage. Lastly, placenta previa is a condition where the placenta covers the cervix, which can cause complications during delivery but does not benefit from a cerclage procedure. The use of cerclage is specifically indicated for managing the risks associated with an incompetent cervix, making it the correct answer.