This is a non-blinded randomized screening trial of asymptomatic singleton pregnancies without prior spontaneous preterm birth who are randomized to either transvaginal ultrasound cervical length screening program (i.e. intervention group) or no screening (i.e. control group). Women are consented and randomized at the time of their routine anatomy scan between 18 0/7 and 23 6/7 weeks. Women randomized in the transvaginal ultrasound cervical length screening will receive a single transvaginal ultrasound cervical length measurement after the anatomy scan. The cervical length will be measured by operators with certification of competence in the technique.

Inclusion criteria are:

• Singleton gestations
• No prior SPTB

Exclusion criteria are:

• Multiple gestations
• History of SPTB in a prior pregnancy
• Rupture of membranes at the time of randomization
• Known major fetal structural (i.e. defined as those that are lethal or require prenatal or postnatal surgery) or chromosomal abnormality
• Fetal death at the time of randomization
• Cerclage in situ at the time of randomization
• Pessary in situ at the time of randomization
• Vaginal bleeding at the time of randomization
• Women who are unconscious, severly ill, mentally handicapped, or under the age of 18 years.

pregnant women