A 32-year-old multiparous woman attends the family planning clinic requesting long-acting reversible contraception. She has a history of irregular menstrual cycles and wants to assess her baseline reproductive status before insertion of a levonorgestrel intrauterine device (LNG-IUD). Which investigation is most appropriate to confirm absence of pregnancy and rule out contraindications before device insertion?

Explanation

## Investigation of Choice Before IUD Insertion ### Clinical Context Before insertion of any intrauterine device (IUD), particularly the LNG-IUD, pregnancy must be definitively excluded and baseline uterine anatomy confirmed. ### Why Serum β-hCG and Transvaginal Ultrasound? **Key Point:** Serum β-hCG is the gold standard for pregnancy detection (sensitivity >99% at 10 mIU/mL) and can detect pregnancy 6–8 days after ovulation, earlier than urine tests. **High-Yield:** Transvaginal ultrasound simultaneously: - Confirms intrauterine pregnancy location (rules out ectopic pregnancy) - Assesses uterine anatomy (excludes fibroids, septate uterus, or other contraindications) - Determines optimal insertion timing and technique - Detects pre-existing IUDs ### Rationale for Combined Approach | Investigation | Purpose | Sensitivity | Timing | |---|---|---|---| | Serum β-hCG | Pregnancy detection | >99% | 6–8 days post-ovulation | | Transvaginal ultrasound | Anatomic assessment + pregnancy location | 100% for IUP | 5 weeks gestation | | Urine pregnancy test | Screening only | 95–98% | 12–14 days post-ovulation | | Pelvic exam | Clinical assessment | Low sensitivity for pregnancy | Operator-dependent | **Clinical Pearl:** In a woman with irregular cycles, dating of pregnancy by urine test alone is unreliable; serum β-hCG quantification provides accurate dating and can be repeated 48 hours later if needed. ### Guideline Alignment [cite:Park 26e Ch 7] recommends pre-IUD assessment including pregnancy exclusion and uterine anatomy confirmation before insertion.