The study aimed to explore the impact of the cervical conization size (CCS) followed by cervical length (CL) changes on preterm birth (PTB) rates in asymptomatic singleton pregnancies compared to pregnancy outcomes (POs) in women with an intact cervix, and to estimate the PTB prevention efficiency in patients with a short cervix (vaginal progesterone alone group (PAG) vs. progesterone-pessary group (PPG)). POs in populations with similar age, ethnicity, residency, education, and harmful habits who underwent cervical conization compared to the women with an intact cervix, and sub-populations with the sufficient CL vs. short cervix, and the PTB prevention efficiency of PAG and PPG were retrospectively analyzed. PTB risks depend on the CCS which is the key point, further, during pregnancy, the larger CCS is associated with the short cervix, and higher PTB risks, notably increased among nulliparous women, and the smaller CCS followed by the sufficient CL and lower PTB risks predominantly observed in women with the prior parity. The USCL assessment is the PTB risk predicting tool, and it can be supplemented with the CCS to increase its diagnostic value. There was no substantial impact on the POs associated with the PTB prevention modes, whereas, the CL changes during pregnancy depending on the CCS is more critical in POs.