What is the appropriate work-up and management plan for a pregnant woman presenting with symptoms of threatened miscarriage, specifically vaginal bleeding during the first trimester?

Work-up for Threatened Miscarriage

Obtain transvaginal ultrasound immediately as the primary diagnostic tool, combined with quantitative beta-hCG level, before performing any digital pelvic examination. 1, 2, 3

Initial Diagnostic Approach

Imaging First - Examination Never Before Ultrasound

• Digital pelvic examination is absolutely contraindicated until ultrasound has definitively excluded placenta previa, low-lying placenta, and vasa previa, as examination before imaging can precipitate catastrophic hemorrhage 1, 2
• Transvaginal ultrasound provides superior resolution compared to transabdominal ultrasound for first trimester evaluation 1, 2, 3
• Perform speculum examination only after ultrasound to assess for cervical lesions, polyps, or inflammation 1

Essential Laboratory Testing

• Quantitative beta-hCG level must be obtained regardless of ultrasound findings to help identify ectopic pregnancies and guide interpretation 1, 2, 3
• Complete blood count to assess hemoglobin if bleeding is moderate to heavy 2
• The discriminatory threshold for beta-hCG is 1,500-2,000 mIU/mL, at which point a normal intrauterine pregnancy must show a gestational sac on transvaginal ultrasound 1, 3, 4

Ultrasound Assessment Components

The ultrasound must systematically evaluate 3:

• Presence and viability of intrauterine pregnancy with fetal cardiac activity
• Location of gestational sac (intrauterine vs. ectopic)
• Presence of subchorionic hematoma
• Cervical length and integrity
• Any free fluid in pelvis suggesting ectopic rupture

Interpretation and Management Based on Findings

If Intrauterine Pregnancy Confirmed with Fetal Cardiac Activity

• Ectopic pregnancy is essentially ruled out (except rare heterotopic pregnancy in <1% of spontaneous conceptions) 1, 2
• Assess for subchorionic hematoma presence 1, 2
• Schedule follow-up ultrasound in 1-2 weeks to monitor progression 1, 2, 3
• Counsel that first trimester bleeding increases risk of preterm delivery (OR 1.56), placental abruption, and small for gestational age infants if pregnancy continues 1, 2, 5

If Pregnancy of Unknown Location (No Intrauterine Pregnancy Visualized)

• Serial beta-hCG measurements every 48 hours until diagnosis is established 1, 2, 3
• In normal pregnancy, beta-hCG levels increase by 80% every 48 hours 4
• Repeat transvaginal ultrasound when beta-hCG reaches discriminatory threshold of 1,500-2,000 mIU/mL 1, 2, 3
• Most pregnancies of unknown location (80-93%) will be early intrauterine or failed intrauterine pregnancies, but 7-20% will be ectopic, requiring vigilant follow-up 1, 2

If Ectopic Pregnancy Suspected or Confirmed

• Immediate specialist consultation is required 2, 3
• Assess hemodynamic stability and prepare for potential surgical intervention 3
• Medical management with methotrexate is highly effective for properly selected patients 4

Critical Pitfalls to Avoid

• Ultrasound misses up to 74% of ectopic pregnancies initially, making serial beta-hCG monitoring critical when initial ultrasound is non-diagnostic 1, 2
• Avoid overinterpretation of single ultrasound that could lead to inappropriate treatment with methotrexate or dilation and curettage, potentially harming a normal early pregnancy 2
• Normal vital signs do not exclude significant placental pathology such as placental abruption, which can present with normal hemodynamics initially but rapidly deteriorate 1

Progesterone Considerations

Progesterone supplementation should not be routinely used for threatened miscarriage, as 400 mg vaginal progesterone nightly until 12 weeks did not increase live birth rates (82.4% vs 84.2%, RR 0.98) 6. However, serum progesterone level may be useful for risk stratification: women with serum progesterone ≥35 nmol/L had a miscarriage rate of only 9.6%, while those with levels <35 nmol/L had a 70.8% miscarriage rate 7.

Follow-Up Protocol

For Viable Intrauterine Pregnancy

• Repeat ultrasound in 1-2 weeks to confirm progression 1, 2, 3
• Monitor for increased bleeding or pain 3
• Counsel about increased risks: antepartum hemorrhage (OR 1.83), preterm delivery (OR 1.56), and need for manual removal of placenta (OR 1.40) 5

For Pregnancy of Unknown Location

• Serial beta-hCG every 48 hours until diagnosis established 2, 3
• Repeat ultrasound at discriminatory threshold 2, 3
• Daily contact until diagnosis confirmed 3
• Gynecology referral for close monitoring 2