II. Interpretation: Gestational age related findings
-
Transvaginal Ultrasound
- Days 35-37: Gestational Sac of 5 mm (bHCG 1500-2000)
- Days 37-40: Yolk Sac (Gestation sac>9-10 mm, confirms intrauterine pregnancy)
- Day 40: Fetal Pole (Gestational Sac>16-18 mm, bHCG 5000)
- Day 45: Fetal Heart Activity (Crown rump length >5 mm, bHCG 17,000)
-
Abdominal Ultrasound
- Day 42: Gestational Sac (bHCG 3500)
- Days 49-50: Embryo 5-10 mm with cardiac activity (bHCG 20,000)
III. Findings: First Trimester Ultrasound
- Gestational Sac Location
- Intrauterine Pregnancy
- Ectopic Pregnancy
- Identification of Embryo
- Assess for Multiple Gestation
- Evaluation of Adnexa
- Menstrual age
- Gestational Sac Size
- Crown Rump Length
- Viability
- Fetal Heart beat
- Growth of Gestational Sac
- Early detection of fetal anomaly
IV. Exam: First Trimester (Transvaginal Ultrasound)
- Gestational Sac (5 weeks gestation, bHCG 1800)
- Round echolucent (black) sac with echogenic ring located in fundus
- Age on mean diameter: (length + width + height)/3
- Yolk Sac (6 weeks gestation)
- Small echogenic walled round sac within Gestational Sac
- May appear more as '=' sign rather than circle
- Presence rules out pseudogestational sac of ectopic
- Embryo (7 weeks gestation, bHCG 20,000)
- Onset as fetal pole dot on the Yolk Sac edge
- Grows at 1 mm per day
- Fetal heart activity by Crown-Rump Length 5 mm
- Crown-Rump Length most reliable dating measure
- Menstrual age (weeks) = Crown-Rump Length (cm) + 6.5
- Table of menstrual ages per Crown-Rump Length
- 6.1 Weeks: 0.4 cm
- 7.2 Weeks: 1.0 cm
- 8.0 Weeks: 1.6 cm
- 9.2 Weeks: 2.5 cm
- 9.9 Weeks: 3.0 cm
- 10.9 Weeks: 4.0 cm
- 12.1 Weeks: 5.5 cm
- 13.2 Weeks: 7.0 cm
- 14.0 Weeks: 8.0 cm