Pregnancy Diagnosis and Dating

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Signs & Symptoms - Baby Clues Galore

CategorySigns
Presumptive (Mother suspects)Amenorrhea, Nausea/Vomiting (N/V), Breast changes (tenderness, enlargement), Fatigue, Urinary frequency, Quickening (fetal movements felt by mother: 18-20 wks primigravida, 16-18 wks multigravida).
Probable (Examiner suspects)Hegar's sign (📌 Softening of Uterine Isthmus), Chadwick's sign (📌 Cyanosis of Cervix/Vagina), Goodell's sign (📌 Good and Soft Cervix), Positive pregnancy test (hCG), Uterine enlargement, Braxton Hicks contractions, Ballottement.
Positive (Definitive proof)Fetal Heart Sounds (FHS) detected, Fetal movements felt by examiner, Ultrasound (USG) evidence (e.g., fetal cardiac activity).

Hormonal Tests - hCG Hormone Hunt

  • Human Chorionic Gonadotropin (hCG): Key hormone confirming pregnancy.
    • Source: Syncytiotrophoblast of placenta.
    • Structure: Glycoprotein; α-subunit (common: LH, FSH, TSH), β-subunit (unique).

      ⭐ The unique β-subunit of hCG (β-hCG) allows for specific pregnancy detection.

  • Detection Methods & Sensitivity:
    • Serum tests: Detect ~5-10 mIU/mL (earlier, more sensitive).
    • Urine tests: Detect ~25 mIU/mL.
  • Clinical Significance of hCG Levels:
    • Doubling Time: Approx. every 48-72 hours in early viable IUP. 📌
    • Peak Level: Around 8-10 weeks gestation, then declines.
    • Discriminatory Zone: hCG 1500-2000 mIU/mL; IUP typically visible on TVS. Hormone levels during pregnancy timeline

Early USG - Sono Peek-a-Boo

Early ultrasound (USG) is pivotal for confirming pregnancy viability and accurately establishing gestational age (GA). Transvaginal Sonography (TVS) offers earlier and more detailed visualization than Transabdominal Sonography (TAS).

  • Key TVS Milestones (approximate):

    • Gestational Sac (GS): Visible at 4.5-5 weeks. First sign.
    • Yolk Sac (YS): Visible at 5-5.5 weeks. Confirms intrauterine pregnancy (IUP).
    • Fetal Pole (embryo) with Cardiac Activity: Visible & detectable at 5.5-6 weeks.
    • TAS findings are typically observed approximately 1 week later than TVS.
  • GA Dating Parameters:

    • 1st Trimester (Most Accurate):
      • Crown-Rump Length (CRL): Most accurate, accuracy ±5-7 days.
    • 2nd/3rd Trimester: Biparietal Diameter (BPD), Head Circumference (HC), Abdominal Circumference (AC), Femur Length (FL) are used.

⭐ Crown-Rump Length (CRL) is the most accurate biometric parameter for gestational age assessment in the first trimester.

TVS showing gestational sac, yolk sac, fetal pole with CRL

Dating & EDC - Due Date Detective

  • Gestational Age (GA): From LMP (clinically used). Fetal Age: From conception (GA - 2 weeks).
  • Naegele's Rule: For EDC. Assumes 28-day cycle. $EDC = (LMP_{day} + 7 days) / (LMP_{month} - 3 months) / (LMP_{year} + 1 year)$. LMP reliability crucial; if uncertain, use USG.
  • Ultrasound (USG) Dating:
    • 1st Trimester (Most Accurate): Crown-Rump Length (CRL). $GA (weeks) \approx CRL (cm) + 6.5$.
      • Use if LMP uncertain or discrepancy >7 days vs LMP.
    • 2nd Trimester: BPD, HC, FL, AC. Accuracy $\pm$7-10 days.
    • 3rd Trimester: Least accurate for dating ($\pm$2-3 weeks); for growth.
  • Correcting EDC:

    ⭐ If 1st-trimester USG dating differs from LMP by >7 days, EDC is based on USG.

    • If 2nd-trimester USG (pre-20 wks) differs by >10-14 days, change EDC.

High‑Yield Points - ⚡ Biggest Takeaways

  • β-hCG: Earliest serum marker (8-9 days post-ovulation).
  • UPT: Positive around 4 weeks from LMP.
  • Gestational sac: First USG sign (TVUS: 4.5-5 weeks).
  • Yolk sac: Confirms IUP (TVUS: 5-6 weeks).
  • Fetal cardiac activity: Seen by TVUS at 5.5-6 weeks.
  • CRL: Most accurate for 1st trimester dating (up to 13+6 weeks).
  • Naegele's rule: Estimates EDD (LMP - 3 months + 7 days), assumes 28-day cycle.

Practice Questions: Pregnancy Diagnosis and Dating

Test your understanding with these related questions

A 45-year-old female with a history of G5P4A0L4 has her last menstrual period (LMP) on August 25, 2014. What is the gestational age in weeks on May 11, 2015?

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Flashcards: Pregnancy Diagnosis and Dating

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Missed Abortion should be suspected if, on USG CRL e_____ mm and no heartbeat is recordedMSD e_____ mm and no embryo is seen

TAP TO REVEAL ANSWER

Missed Abortion should be suspected if, on USG CRL e_____ mm and no heartbeat is recordedMSD e_____ mm and no embryo is seen

7; 25

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