###Human: I have 2. 9 cm of cervix length at 16 weeks. Do I need cerclage or bed rest now? ###Assistant: Hi. Cervical length should be around 3.5 cm to 4 cm at 16 weeks. But some women do not have problems in pregnancy throughout the weeks even at 2.5 cm length. On ultrasound, we need to have a full bladder (means control of urination) to measure the exact length of the cervix. I presume that you were on a full bladder during the scan and also in the light of your preterm history, you must be having a shorter cervix. But there are other USG findings such as ballooning of lower segment of a uterus and open OS to take an emergency procedure of cerclage. Now cerclage is not practiced widely, and it is a thing of past. You need a bed rest till about seven months of gestation. Progesterone is a perfect one to be taken now and follow your gynecologist advice.