Pregnancy Viability Tests - Complete Guide

What is a "Viability Test"?

1. The pregnancy is located inside the uterus (not ectopic)
2. The embryo/fetus is alive (cardiac activity is present)
3. Development is progressing normally for the gestational age

Tests Used to Assess Pregnancy Viability

1. Serum Beta-hCG (Blood Test)

• Measures the pregnancy hormone human chorionic gonadotropin (hCG)
• Detects pregnancy as early as 8-10 days after conception (before a missed period)
• In a healthy early pregnancy, hCG levels double approximately every 48-72 hours
• A single level tells you pregnancy exists; serial hCG measurements (two draws 48 hrs apart) tell you if it's progressing normally
• Declining or plateauing hCG suggests a failing pregnancy or ectopic pregnancy
• Limitation: Cannot show heart formation, location, or structure - only biochemical evidence of pregnancy

2. Transvaginal Ultrasound (TVS) - THE GOLD STANDARD for Early Viability

• The transvaginal probe is placed gently inside the vagina - it sits much closer to the uterus than an abdominal probe
• Significantly more sensitive than transabdominal ultrasound, especially before 10-11 weeks
• At 8 weeks transvaginally, fetal heart rate detects in ~60% of cases; at 9 weeks, ~87% - vs only 22% and 56% respectively with transabdominal approach (PubMed PMID: 8694073)
• Key rule (Society of Radiologists in Ultrasound): If the embryo's crown-rump length (CRL) is ≥7 mm and NO heartbeat is seen, this is considered diagnostic of pregnancy failure

3. Transabdominal Ultrasound

• Probe placed on the abdomen over gel
• Less sensitive in the first trimester compared to transvaginal
• Becomes equally useful after ~12 weeks when the uterus is larger
• Standard for the 18-20 week anatomy scan

Which Test Can Show Whether the Baby's Heart is Formed?

Fetal Echocardiography - The Most Detailed Heart Assessment

• Standard timing: 18 to 22 weeks of pregnancy (most complete information)
• Early fetal echocardiography: 12 to 16 weeks in specialized centers
• Very early (research settings): from 11 weeks onward

• All 4 chambers of the heart
• Heart valves (mitral, tricuspid, aortic, pulmonary)
• Major blood vessels (aorta, pulmonary artery)
• Blood flow direction using Color Doppler
• Fetal heart rate and rhythm
• Congenital heart defects

• Sensitivity: 78.6% - 89% for detecting congenital heart disease
• Specificity: 98.9% - 100%
• Best results after 11 weeks, with full anatomy visible in ~98% of cases by week 11

• 8 weeks: Only 52% of scans can show 4 chambers
• 10 weeks: 80% can show 4 chambers
• 11 weeks: 98% can show 4 chambers (with Color Doppler assistance)

Quick Summary: Which Test for What?

Important Notes

• A normal routine ultrasound at 6-8 weeks confirms cardiac activity (heartbeat present/absent), but does not show heart structure in detail
• If no heartbeat is seen at 6 weeks, it does not always mean the pregnancy has failed - the gestational age estimate may be slightly off, or development may be slightly slow. A repeat scan 1-2 weeks later is usually recommended before drawing conclusions
• Fetal echocardiography is specifically recommended for women with a family history of congenital heart disease, a fetus with abnormal nuchal translucency (NT) at 11-13 weeks, maternal diabetes, or certain infections during pregnancy

Pregnancy Viability Tests - Complete Guide

What Does "Viability" Mean?

• The embryo/fetus is alive (cardiac activity is present)
• The pregnancy is inside the uterus (not ectopic)
• Development matches the gestational age

Tests Used to Assess Pregnancy Viability

1. Serum Beta-hCG (Blood Test)

• Detects pregnancy as early as 8-10 days after conception (before a missed period)
• In a healthy early pregnancy, hCG levels rise rapidly until 9-10 weeks, then plateau
• Serial measurements (two draws, 48 hours apart) are far more useful than a single value:
  • Normal pregnancy: hCG rises by at least 53% every 48 hours (median rise ~124% in 2 days)
  • Failing/ectopic pregnancy: hCG rises more slowly, plateaus, or falls
  • Spontaneous abortion: hCG decreases by 21-35% in 2 days
• No single hCG value can distinguish a normal from a pathologic pregnancy - serial values are key
• Limitation: Cannot show heartbeat, location in the uterus, or heart structure

- Tintinalli's Emergency Medicine, p. 658

2. Serum Progesterone (Blood Test)

• Levels are relatively constant in the first 8-10 weeks of normal pregnancy
• Falls when pregnancy fails
• Progesterone ≤5 ng/mL: nearly 100% of pregnancies will be pathologic
• Progesterone >25 ng/mL: 97% sensitivity for a viable intrauterine pregnancy
• Considerable overlap exists between normal and abnormal ranges - used alongside hCG and ultrasound, not alone

- Tintinalli's Emergency Medicine

3. Transvaginal Ultrasound (TVS) - THE GOLD STANDARD for Early Viability

- Rosen's Emergency Medicine (textbook table)

• No gestational sac when hCG is ≥3,000 mIU/mL → abnormal
• No yolk sac when gestational sac ≥13 mm → abnormal
• Crown-rump length (CRL) of 5 mm with no heartbeat → abnormal
• No embryo when gestational sac ≥25 mm → abnormal
• No heartbeat after 10-12 weeks gestational age → abnormal

Which Test Shows Whether the Baby's Heart is Formed?

Fetal Echocardiography - The Most Detailed Heart Assessment

• Standard timing: 18 to 22 weeks (most complete view, standard of care)
• Early fetal echo: 12 to 16 weeks at specialized centers
• From 11 weeks onward with best results (particularly combined with Color Doppler)

• All 4 chambers (right/left atria and ventricles)
• All 4 heart valves (mitral, tricuspid, aortic, pulmonary)
• Major outflow vessels (aorta, pulmonary artery)
• Aortic and ductal arches
• Inferior vena cava, pulmonary veins
• Blood flow direction using Color Doppler
• Heart rate and rhythm
• Congenital heart defects

• Sensitivity for congenital heart disease: 78.6% to 89%
• Specificity: 98.9% to 100%
• Best results are achieved after 11 weeks; ideal standard exam at 18-22 weeks

• Family history of congenital heart disease (CHD)
• Abnormal nuchal translucency (NT) at 11-13 week scan
• Maternal diabetes or certain infections during pregnancy
• Previous baby with CHD
• Abnormal cardiac findings on routine anatomy scan

Quick Summary Table

Important Points to Remember

• A heartbeat seen at 6-7 weeks gives a 70-90% chance of the pregnancy continuing successfully
• No heartbeat at exactly 6 weeks does not always mean pregnancy failure - the dating may be slightly off. A repeat scan 7-10 days later is usually recommended before any conclusions are made
• A routine viability scan confirms cardiac activity (heartbeat present or absent) but does not show detailed heart structure
• Fetal echocardiography is the only test that can tell you whether the baby's heart chambers, valves, and vessels are properly formed