{
  "_meta": {
    "version": "1.0.0",
    "source": "American College of Obstetricians and Gynecologists (ACOG) general pregnancy timeline",
    "lastUpdated": "2026-05-17",
    "notes": "Gestational age is measured from the first day of the last menstrual period (LMP). This data is informational only and is not medical advice."
  },
  "trimesters": [
    {
      "number": 1,
      "label": "First Trimester",
      "startWeek": 1,
      "endWeek": 12,
      "averageWeightGainKg": [0, 2],
      "keyMilestones": [
        "Week 4: Implantation completes; heartbeat begins forming",
        "Week 6: Embryonic heartbeat detectable on ultrasound",
        "Week 8: All major organs begin to form (embryo becomes fetus at week 10)",
        "Week 12: Fetus is fully formed at miniature scale; risk of miscarriage drops significantly"
      ],
      "commonSymptoms": ["Morning sickness", "Fatigue", "Breast tenderness", "Frequent urination"]
    },
    {
      "number": 2,
      "label": "Second Trimester",
      "startWeek": 13,
      "endWeek": 26,
      "averageWeightGainKg": [5, 7],
      "keyMilestones": [
        "Week 16: Sex often determinable on ultrasound",
        "Week 18-22: Anatomy scan performed",
        "Week 20: Halfway point; quickening (first felt movement)",
        "Week 24: Viability threshold reached with intensive neonatal care"
      ],
      "commonSymptoms": ["Increased energy", "Visible bump", "Back pain", "Heartburn"]
    },
    {
      "number": 3,
      "label": "Third Trimester",
      "startWeek": 27,
      "endWeek": 40,
      "averageWeightGainKg": [4, 6],
      "keyMilestones": [
        "Week 28: Eyes open; lungs continue maturing",
        "Week 32: Bones fully formed but soft",
        "Week 37: Considered full-term",
        "Week 40: Estimated due date (EDD)"
      ],
      "commonSymptoms": ["Braxton-Hicks contractions", "Shortness of breath", "Swelling", "Trouble sleeping"]
    }
  ]
}