Ultrasound in third trimester pregnancy , placenta and amniotic fluid , diagnosis ultrasound in third trimester

1. USG IN OB & GY
3RD TRIMESTER,
PLACENTA & AMNIOTIC FLUID
REF- ULTRASOUND IN OBSTETRICS AND GYNECOLOGY
A PRACTICAL APPROACH
FIRST EDITION
EDITOR- ALFRED ABUHAMAD, MD

2. MAIN OBJECTIVES
• Fetal growth, Position of the placenta, Assessment of amniotic fluid
• Beyond 28th week of gestation = 3rd trimester
• > 28 wk scan dating is less accurate than earlier gestation

3. COMPONENTS OF 3RD TRIMESTER USG
• Cardiac activity
• Fetal size ( biometry and estimation of fetal weight)
• Presentation and lie
• Fetal anatomy
• Placenta localization
• Amniotic fluid assessment
• Evaluation of adnexae

4. ASSESSMENT OF FETAL WEIGHT
• Should not performed for dating ( range +_ 3 wks)
• BPD and HC are more precise markers of gestational age than AC and FL
• AC is most accurate and sensitive for fetal weight

5. INTRAUTERINE GROWTH RESTRICTION
• EFW below 10th percentile for gestational age
• Two types – symmetrical ( early) and asymmetrical ( late ) IUGR
• IUGR – asso with fetal infection and choromosomal abnl
• Mx is similar for both types and this distinction is no longer clinical value

6. IUGR
• First suspicion from lagging fundal heights on prenatal visit
• USG - exclude fetal malformations ,fetal surveillance and amniotic fluid
evaluation
• Fetal surveillance – cardiotocography, umbilical artery Doppler, MCA doppler

7. FETAL MACROSOMIA
• Fetal weight > 4000 or 4500 grams irrespective of gestational age
• Predisposing factors – maternal DM, prior history, maternal obesity
,gestational age >42 wks
• Hadlock’s formula to predict fetal weight ( mean absolute error 13% for >4500
G)

8. PLACENTAL ABNORMALITIES
• Placenta previa
• Vasa previa
• Morbidly adherent placenta
• Placenta accreta
• Placenta abruption