Hello Doctor! Im 28 yrs female, 17 weeks pregnant now. In my 12th week scan report, Cervix length is mentioned as 2.8cm. Kindly tell me it is correct in size for the time. But I heard that it should be 3-4 cm, otherwise I should take bed rest. Also heard that at the scan of 20th week, cervix length should be greater than 3cm otherwise it leads to premature delivery. Please clarify me on this. Thanks in advance.