What are the recommended steps for evaluating a 10-week pregnancy based on bedside findings?

Recommended Steps for Evaluating a 10-Week Pregnancy Based on Bedside Findings

The main goal of a 10-week ultrasound examination is to confirm the presence and location of the gestational sac, determine chorionicity and amnionicity if multiple gestations are present, provide accurate pregnancy dating, and document embryonic or fetal cardiac activity. 1

Key Components of the 10-Week Ultrasound Evaluation

Initial Assessment

• Confirm intrauterine pregnancy location by identifying the gestational sac with surrounding echogenic chorionic reaction 1
• Establish viability by documenting embryonic or fetal cardiac activity 2
• Determine the number of gestations (single vs multiple) 1
• Measure crown-rump length (CRL) for accurate pregnancy dating and expected delivery date calculation 2, 3

Multiple Gestation Assessment (if applicable)

• Determine chorionicity and amnionicity, which is most accurate in the first trimester 1
• For dichorionic diamniotic gestations, identify two separate gestational sacs each with surrounding echogenic chorionic reactions 1
• For monochorionic gestations, identify a single gestational sac with peripheral chorionic reaction 1
• Look for the intertwin membrane, which is typically identifiable by 10 weeks on transvaginal ultrasound (TVUS) 1
• Note that the number of yolk sacs can sometimes be used as an indicator for assessing amnionicity, though this may sometimes be erroneous 1
• Measure and document any crown-rump length (CRL) discrepancy between twins, as discordance ≥10% has been associated with adverse outcomes 1

Anatomical Survey

• At 10 weeks, a basic anatomical assessment can be performed, though it is more limited than later scans 4
• Evaluate the skull, brain, spine, abdomen, and limbs 4
• Assess nuchal translucency if between 10-14 weeks (ideally 11-14 weeks) 1, 4
• Note that increased nuchal translucency at 10-14 weeks may be a sign of chromosomal disorders or severe skeletal dysplasia 1

Technical Considerations

• Begin with transabdominal ultrasound for initial assessment 1
• If visualization is suboptimal, supplement with transvaginal ultrasound for better resolution, especially for:
  • Confirming the presence of an intertwin membrane 1
  • Evaluating fetal anatomy in detail 4
  • Assessing early pregnancy structures 1, 4

Important Clinical Considerations

• The 10-week scan provides baseline measurements for future growth assessment 3
• Finding a femur length below the 5th percentile for gestational age warrants further evaluation 1
• Routine early ultrasound improves detection of multiple pregnancies and major fetal abnormalities 5
• Ultrasound measurements by trained physicians can be completed in less than one minute and provide accurate gestational age assessment 6
• The optimal gestational age for examining both cardiac and non-cardiac anatomy is from the beginning of the 12th week to the end of the 13th week of gestation 4

Common Pitfalls to Avoid

• Failing to determine chorionicity in multiple gestations, which is crucial for risk stratification and management 1
• Missing the intertwin membrane in multiple gestations, which requires careful examination with TVUS 1
• Overlooking CRL discordance in multiple gestations, which can predict adverse outcomes 1
• Assuming absence of an intertwin membrane indicates monoamnionicity, as the amnion may not yet be visible at 10 weeks 1
• Relying solely on transabdominal imaging when structures are not well visualized 1, 4