Mcdonald stitch is applied in the following conditions except:: (A) Incompetent os, (B) Septate uterus, (C) Placenta previa, (D) Bad obstetrical history
Answer is C. Contraindications to Circlage operation:

Intra uterine infection
Ruptured membranes
H/o vaginal bleeding
Severe uterine irritability
Cervical dilatation > 4 cm