Cervical Length and Preterm Birth Risk Calculator

Calculate preterm birth risk from mid-trimester cervical length measurement. CL <25 mm at 18-24 weeks in singleton or CL <35 mm in twins increases preterm birth risk. Guides progesterone supplementation and cerclage decisions.

Weight
Height
Clinical Guidance

BMI is a screening measure of body size, not a direct measure of body fat. The standard WHO categories are underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), and obese (≥30).

BMI can overestimate body fat in athletes with high muscle mass and underestimate it in older adults with low muscle mass. Interpret it alongside waist circumference and clinical context rather than as a standalone diagnosis.

⚕ Clinical Disclaimer: These calculators are for educational and reference purposes only. Always verify results with qualified clinical judgment and current clinical guidelines. Do not use as a sole basis for medical decisions.
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How It Works

Calculate preterm birth risk from mid-trimester cervical length measurement. CL <25 mm at 18-24 weeks in singleton or CL <35 mm in twins increases preterm birth risk. Guides progesterone supplementation and cerclage decisions

Each component has a specific meaning:

  • Mid-trimester cervical length measurement — The mid-trimester cervical length measurement recorded for the scenario being assessed.

Note: Interpret the cervical length ptb risk result against the thresholds and context described above.

How to Use

Enter the mid-trimester cervical length measurement for the scenario you are assessing. Calculate preterm birth risk from mid-trimester cervical length measurement. CL <25 mm at 18-24 weeks in singleton or CL <35 mm in twins increases preterm birth risk. Guides progesterone supplementation and cerclage decisions. Use the cervical length ptb risk result to inform your calculation.

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Frequently Asked Questions