Pregnancy Confirmation

When to Test and When an Ultrasound Is Needed

If you suspect you may be pregnant or have a positive home pregnancy test, it is natural to have questions about what comes next. Early pregnancy diagnosis focuses on confirming whether a pregnancy exists, where it is located, and whether it is developing normally.

How Is Pregnancy Confirmed?

Pregnancy is initially confirmed by detecting the hormone human chorionic gonadotropin (β-hCG) in the urine or blood.

When Does a Pregnancy Test Become Positive?

With sensitive pregnancy tests, β-hCG can be detected as early as 8–9 days after ovulation, which may be several days before a missed period. However: 

• Test sensitivity varies depending on the brand and detection threshold
  
• Blood β-hCG tests are more sensitive than urine tests
  

A positive urine or blood pregnancy test confirms pregnancy, but it does not provide information about:

• Whether the pregnancy is viable
  
• Where the pregnancy is located (inside or outside the uterus)

When Is an Ultrasound Used to Confirm Pregnancy?

Ultrasound is used to:

• Confirm the location of the pregnancy
  
• Establish gestational age
  
• Assess early pregnancy development
  
• Determine the number of embryos
  
• Evaluate other pelvic structures, such as uterine fibroids or ovarian cysts
  

Transvaginal ultrasound (TVS) is the preferred method in early pregnancy.

What Can Be Seen on Early Pregnancy Ultrasound?

Typical findings on transvaginal ultrasound include:

• 4–5 weeks
  
  • Intrauterine gestational sac (first visible sign of pregnancy)
    
• ~5 weeks
  
  • Yolk sac becomes visible
    
• ~6 weeks
  
  • Embryo may be seen
    

It is important to distinguish a true gestational sac from a pseudosac, which is a fluid collection within the uterine cavity that may occur in ectopic pregnancy. If this finding is seen without other confirming features—especially in women with pain or bleeding—further evaluation is required.

Fetal Heartbeat in Early Pregnancy

• Fetal cardiac activity may be detected when the embryo measures as small as 2–3 mm
  
• Cardiac activity should be visible once the embryo measures ≥7 mm in a viable pregnancy
  

If cardiac activity is not yet seen, further evaluation may include repeat ultrasound or blood testing, depending on gestational age and clinical symptoms.

Is Early Pregnancy Ultrasound Safe?

Yes. Diagnostic ultrasound is considered safe in pregnancy.

• No causal relationship has been demonstrated between diagnostic ultrasound and adverse pregnancy outcomes
  
• Ultrasound is performed only when medically indicated
  
• The ALARA principle (As Low As Reasonably Achievable) is followed to minimize exposure
  
• M-mode, rather than Doppler, is used to assess fetal heart activity in early pregnancy
  

Indications for First-Trimester Ultrasound

A first-trimester ultrasound may be recommended to:

• Confirm an intrauterine pregnancy
  
• Estimate gestational age
  
• Confirm fetal cardiac activity
  
• Diagnose and evaluate multiple pregnancy
  
  • Including chorionicity and amnionicity
    
• Assess for early fetal anomalies (when appropriate)
  
• Measure nuchal translucency
  
• Evaluate uterine abnormalities or pelvic masses
  
• Assess suspected ectopic pregnancy
  
• Evaluate vaginal bleeding or pelvic pain
  
• Assist with procedures such as embryo transfer, chorionic villus sampling wtc
  

Early pregnancy assessment can provide clarity and reassurance during the first weeks.

If you want more information on how to care for yourself during the early weeks of pregnancy, click here.

References

1. Cunningham FG, Leveno KJ, Bloom SL, et al.
   Williams Obstetrics. 25th ed. New York: McGraw-Hill Education; 2018.
   
2. American College of Obstetricians and Gynecologists (ACOG).
   Ultrasonography in Pregnancy. ACOG Practice Bulletin No. 175.
   Obstet Gynecol. 2016; reaffirmed 2022–2024.