ULTRA - Semis Pt. 2

OBSTETRIC ULTRASOUND

• Diagnostic ultrasound is used in obstetrics for many years

• Important for examining pregnant women

• Can be used any time during pregnancy when clinically indicated

OBSTETRIC ULTRASOUND

• Uses sound waves

• Produces images of:

  • Embryo / fetus

  • Uterus

  • Ovaries

• No ionizing radiation

• No known harmful effects

• Preferred method for monitoring pregnancy

• STAGE 1: 18–22 WEEK SCAN

• STAGE 2: 32–36 WEEK SCAN

INDICATIONS OF OBSTETRIC ULTRASOUND

STAGE 1: 18–22 WEEK SCAN

Best time to:

1. Establish gestational age accurately

2. Diagnose multiple pregnancies

3. Diagnose fetal abnormalities

4. Locate the placenta and identify placenta previa risk

5. Recognize:

   • Myomas

   • Other pelvic masses

STAGE 2: 32–36 WEEK SCAN

Best time to:

1. Recognize intrauterine growth retardation (IUGR)

2. Detect missed fetal abnormalities

3. Confirm fetal presentation and position

4. Locate the placenta accurately

5. Assess amniotic fluid

6. Exclude complications:

   • Myoma

   • Ovarian tumor

• Gestational Sac

• Yolk Sac

• Embryo

PREGNANCY FINDINGS

Gestational Sac

• Earliest evidence of pregnancy

• Appears as fluid-filled sac

• Seen best with endovaginal ultrasound

• Double echogenic ring

• Anechogenic residual uterine cavity

Gestational Sac Appearance

Inner ring

• Uniform echogenicity

• ≥ 2 mm thick

Outer ring

• Thin

• Does not completely encircle sac

5–6 weeks

Gestational Sac Size Progression

• 1–2 cm

8 weeks

Gestational Sac Size Progression

• occupies ½ of uterus

9 weeks

Gestational Sac Size Progression

• occupies 2/3 of uterus

10 weeks

Gestational Sac Size Progression

• fills uterus

(Length + AP + Width) ÷ 3

Mean Gestational Sac Dimension Formula

Length

longest internal (longitudinal)

AP

widest perpendicular to length

Width

widest transverse

Yolk Sac

• Appears at 7 weeks

• Site of earliest blood cell formation

• Disappears at 11 weeks

Embryo

Visible at 8 weeks

9–10 weeks

Embryo

• Head distinguishable

• Movements seen

10 weeks

Embryo

• More human appearance

After 12 weeks

Embryo

• Skull visible

• Small gestational sac

• Fetal death (spontaneous abortion)

• Empty uterus

• Large uterus

FIRST TRIMESTER ABNORMALITIES

Small gestational sac

Cause: Blighted ovum (anembryonic gestation)

Fetal death (spontaneous abortion)

• May have:

  • Bleeding

  • Abdominal cramps

• Patient may still feel pregnant

Empty uterus

• History of:

  • Amenorrhea

  • Followed by bleeding

• Hydatidiform mole

• Choriocarcinoma

• Intrauterine bleeding

• Uterine myoma (fibroids)

Causes of Large uterus

• Crown-Rump Length (CRL)

• Biparietal Diameter (BPD)

• Fronto-Occipital Diameter (FOD)

• Cephalic Index

• Head Circumference (HC)

• Abdominal Circumference (AC)

• Femur Length (FL)

• Amniotic Fluid Index (AFI)

• Placental Location

• Fetal Heart Rate (FHR)

FETAL BIOMETRY (SIZE & AGE)

Crown-Rump Length

• Most reliable up to 11 weeks

• Confirms:

  • Viability

  • Due date

Measurement

• Crown → Rump

Gestational age (weeks) = CRL (cm) + 6.5

CRL Formula

Biparietal Diameter (BPD)

• Most reliable 12–26 weeks

• Measures:

  • Width of fetal head

• From parietal bone to parietal bone

Fronto-Occipital Diameter (FOD)

• Longest skull axis

• Measured:

  • Outer edge to outer edge

  • At level of BPD

CI = (BPD / FOD) × 100

Cephalic Index Formula

70–86

Normal Cephalic Index

Head Circumference

• Measures outer skull perimeter

• Evaluates:

  • Head size

  • Growth abnormalities

HC = (BPD / FOD) × 1.57

HC Formula

Abdominal Circumference

• Best indicator of fetal growth & nutrition

Uses

• Detect:

  • IUGR

  • Macrosomia

Measurement

• Level of:

  • Liver

  • Stomach

  • Umbilical portion of left portal vein

AC = (AP + Transverse) × 1.57

AC Formula

Femur Length (FL)

• Estimates fetal age

• Evaluates skeletal development

• Measures femur length

Amniotic Fluid Index (AFI)

Measures amniotic fluid volume

• Oligohydramnios (low)

• Polyhydramnios (high)

AFI Detects

Placental Location

• Determines if placenta is:

  • Anterior

  • Posterior

  • Fundal

  • Previa

110–160 bpm

Normal Fetal Heart Rate