Low hCG & Missed Period: Causes, Risks & What to Do

Low hCG with a missed period suggests early pregnancy complications or non-pregnant causes.

Pregnancy-Related Causes

• Very Early Pregnancy: Ovulation later than thought → hCG below detection threshold. Repeat in 48–72 hrs (should double).
• Chemical Pregnancy: Implantation occurs, hCG rises briefly, then falls before ultrasound visualization. Early miscarriage (~50% of conceptions).
• Ectopic Pregnancy: hCG rises abnormally (slow, plateau, or decline). Medical emergency. Risk factors: PID, prior ectopic, tubal surgery, IUD, IVF. Symptoms: unilateral pain, vaginal bleeding, shoulder tip pain (diaphragmatic irritation).
• Failing Intrauterine Pregnancy: Suboptimal rise (<53% in 48h), then decline.
• Molar Pregnancy: Very high hCG (usually), but can be low if failing.

Non-Pregnancy Causes of Low hCG

• Perimenopause: Elevated FSH/LH can cross-react with some hCG assays (rare).
• Pituitary hCG: Low levels (<5–10 mIU/mL) in postmenopausal women.
• Heterophilic Antibodies: Assay interference.
• Medications: Certain fertility drugs (hCG trigger) — but would be high.

Action Plan

1. Quantitative Serum β-hCG (Repeat in 48 hrs): Determines trajectory.
2. Transvaginal Ultrasound: When hCG >1500–2000 mIU/mL (discriminatory zone). No IUP + hCG >discriminatory zone → ectopic until proven otherwise.
3. Progesterone: Low (<5 ng/mL) suggests non-viable/ectopic; high (>20–25) suggests viable IUP.
4. If Ectopic Suspected: Methotrexate (if stable, unruptured, hCG <5000, no fetal cardiac activity) or Surgery (salpingostomy/salpingectomy).

When to Seek Immediate Care

• Severe abdominal/pelvic pain.
• Syncope, dizziness, shoulder pain.
• Heavy vaginal bleeding.