First trimester obstetric sonography encompasses examinations from conception through 13 weeks 6 days, covering pregnancy confirmation, dating, viability assessment, early anatomy screening, and the nuchal translucency measurement for chromosomal risk stratification. The first trimester scan is often the patient’s first introduction to prenatal imaging.
Transabdominal and transvaginal scanning establish gestational age via crown-rump length (CRL) measurement, confirm intrauterine location (ruling out ectopic pregnancy), assess fetal cardiac activity, evaluate the uterus and adnexae, and document the number of embryos and chorionicity in multiple gestations. The combined first-trimester screen integrates NT measurement, nasal bone assessment, and serum biochemistry to calculate trisomy risk. The early anatomy survey identifies major structural anomalies amenable to first-trimester detection.
First trimester scanning is covered under the ARDMS OB/GYN specialty within the RDMS credential. Transvaginal technique is essential for early pregnancy assessment, particularly before 9–10 weeks when transabdominal imaging is limited. Sonographers must be proficient in recognizing ectopic pregnancy, miscarriage types, and early anomalies while communicating with sensitivity in emotionally charged clinical situations.