{
  "id": "miscarriage-risk",
  "version": "e67946432484",
  "status": "published",
  "name": "Miscarriage Risk Calculator",
  "question": "What is my miscarriage risk?",
  "summary": "Shows the published miscarriage risk for your age (Magnus 2019, 421,201 pregnancies) and, after a normal scan with a heartbeat at 6 to 10 weeks, the risk by week (Tong 2008).",
  "category": "health",
  "subcategory": "clinical",
  "url": "https://www.acalculator.org/health/miscarriage-risk-calculator",
  "markdown": "https://www.acalculator.org/health/miscarriage-risk-calculator.md",
  "kind": "function",
  "method": "Two published tables: miscarriage risk by maternal age group (Magnus 2019), and risk after a normal scan with a heartbeat by completed week, 6 to 10 (Tong 2008).",
  "assumptions": [
    "The age table counts all recognized pregnancies in Norway, 2009 to 2013, with induced abortions handled as in the paper.",
    "The week table is from 696 women with no symptoms and one baby with a heartbeat at their first visit in Australia.",
    "The two numbers come from different studies and are not combined."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "age": {
        "title": "Your age",
        "description": "Your age in whole years at the start of the pregnancy.",
        "type": "integer",
        "minimum": 13,
        "maximum": 55
      },
      "scan": {
        "title": "Normal scan with a heartbeat?",
        "description": "Whether an ultrasound at 6 to 10 weeks showed one baby with a heartbeat, with no bleeding or pain.",
        "type": "string",
        "enum": [
          "no",
          "yes"
        ]
      },
      "wk": {
        "title": "Weeks pregnant at that scan",
        "description": "Completed weeks of pregnancy at the scan, 6 to 10 (6 weeks and 3 days counts as 6).",
        "type": "integer",
        "minimum": 6,
        "maximum": 10
      }
    }
  },
  "outputs": {
    "ageRisk": {
      "label": "Risk for your age",
      "description": "The share of pregnancies that ended in miscarriage for women in your age group (Magnus 2019).",
      "format": "percent"
    },
    "ageGroup": {
      "label": "Age group",
      "description": "The age group of the published table.",
      "format": "text"
    },
    "afterScan": {
      "label": "Risk after a normal scan at this week",
      "description": "The share of women with no symptoms and a normal scan at this week who later miscarried (Tong 2008).",
      "format": "percent"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "scan": "no",
      "wk": 8,
      "age": 30
    },
    "outputs": {
      "ageRisk": 10.8,
      "ageGroup": "30 to 34"
    },
    "text": "For age 30, the published miscarriage risk is 10.8% (age group 30 to 34)."
  },
  "examples": [
    {
      "given": {
        "age": 30,
        "scan": "no"
      },
      "expect": {
        "ageRisk": 10.8,
        "ageGroup": "30 to 34"
      },
      "source": "Magnus 2019, BMJ, Table 1: age 30 to 34, 13,362 of 123,266 pregnancies, 10.8%"
    },
    {
      "given": {
        "age": 27,
        "scan": "no"
      },
      "expect": {
        "ageRisk": 9.8,
        "ageGroup": "25 to 29"
      },
      "source": "Magnus 2019, Table 1: age 25 to 29, 9.8% (the lowest group)"
    },
    {
      "given": {
        "age": 42,
        "scan": "yes",
        "wk": 7
      },
      "expect": {
        "ageRisk": 32.2,
        "ageGroup": "40 to 44",
        "afterScan": 4.2
      },
      "source": "Magnus 2019, Table 1: age 40 to 44, 32.2%; Tong 2008: 4.2% after a normal visit at 7 weeks"
    },
    {
      "given": {
        "age": 46,
        "scan": "yes",
        "wk": 9
      },
      "expect": {
        "ageRisk": 53.6,
        "ageGroup": "45 or older",
        "afterScan": 0.5
      },
      "source": "Magnus 2019, Table 1: 45 and over, 53.6%; Tong 2008: 0.5% at 9 weeks"
    },
    {
      "given": {
        "age": 19,
        "scan": "yes",
        "wk": 6
      },
      "expect": {
        "ageRisk": 15.8,
        "ageGroup": "under 20",
        "afterScan": 9.4
      },
      "source": "Magnus 2019, Table 1: under 20, 15.8%; Tong 2008: 9.4% at 6 completed weeks"
    }
  ],
  "sources": [
    "Magnus MC, Wilcox AJ, Morken NH, Weinberg CR, Håberg SE. Role of maternal age and pregnancy history in risk of miscarriage: prospective register based study. BMJ. 2019;364:l869. https://doi.org/10.1136/bmj.l869",
    "Tong S, Kaur A, Walker SP, Bryant V, Onwude JL, Permezel M. Miscarriage risk for asymptomatic women after a normal first-trimester prenatal visit. Obstet Gynecol. 2008;111(3):710-714. https://doi.org/10.1097/AOG.0b013e318163747c"
  ],
  "related": [],
  "changelog": [
    {
      "date": "2026-09-30",
      "note": "Published after this site's editorial review against the cited sources (no clinician review); the page notices say so."
    },
    {
      "date": "2026-09-30",
      "note": "The answer sentence prints one percent sign, not two."
    }
  ]
}