What should you know?
Early pregnancy appears in stages: gestational sac, yolk sac, embryo and then cardiac activity. Timing varies with ovulation and implantation, so a difference of several days can be normal.
In the first trimester, correctly measured crown-rump length (CRL) is the most reliable ultrasound measure for dating. A single small difference is not the same as growth restriction; interval change matters.
Common symptoms and signs
- The gestational sac is usually the first visible structure
- Cardiac activity often appears around 6–7 weeks
- CRL is used for early dating
- Ultrasound dating may differ from menstrual dates
Diagnosis and the role of ultrasound
Transvaginal ultrasound provides the most detail early in pregnancy and assesses location, sac structures, embryo CRL, cardiac activity, uterus and adnexa.
- Intrauterine pregnancy location
- CRL and heart rate
- Gestational and yolk sac appearance
- Hematoma or adnexal abnormality
Treatment and next steps
When dating or viability remains uncertain, the clinician schedules a repeat scan at an evidence-based interval. Repeating too soon may add no useful information and increase anxiety.
When is urgent care needed?
- Severe or one-sided pelvic pain
- Heavy bleeding, weakness or fainting
- Shoulder pain or rapidly worsening condition