OASI Perineal Obstetric Tear Risk Score

Calculate risk of obstetric anal sphincter injury (OASI, 3rd/4th degree tears) using OASI Care Bundle risk factors: nulliparity, Asian ethnicity, birth weight >4 kg, instrumental delivery. Risk 0.25-10% depending on factors.

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 risk of obstetric anal sphincter injury (OASI, 3rd/4th degree tears) using OASI Care Bundle risk factors: nulliparity, Asian ethnicity, birth weight >4 kg, instrumental delivery. Risk 0.25-10% depending on factors

Each component has a specific meaning:

  • OASI Care Bundle risk factors: nulliparity — The oasi care bundle risk factors: nulliparity recorded for the scenario being assessed.
  • Asian ethnicity — The asian ethnicity recorded for the scenario being assessed.
  • Birth weight >4 kg — The birth weight >4 kg recorded for the scenario being assessed.
  • Instrumental delivery — The instrumental delivery recorded for the scenario being assessed.

Note: Interpret the oasi perineal tear risk result against the thresholds and context described above.

How to Use

Enter the OASI Care Bundle risk factors: nulliparity, Asian ethnicity, birth weight >4 kg, instrumental delivery for the scenario you are assessing. Calculate risk of obstetric anal sphincter injury (OASI, 3rd/4th degree tears) using OASI Care Bundle risk factors: nulliparity, Asian ethnicity, birth weight >4 kg, instrumental delivery. Risk 0.25-10% depending on factors. Use the oasi perineal tear risk result to inform your calculation.

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Frequently Asked Questions