Obstetrics - Ultrasound exam, CTG, Doppler flow studies, Biophysical profile, Pre-natal diagnosis Flashcards
Assessments done in early pregnancy scan
Assessment of anomaly scan
Assessments in 3rd trimester scan
Indications of extra ultrasound scans during pregnancy
Compare use of TVUS vs TAUS during pregnancy
TVUS: better visualization of lower pelvis, more appropriate for
- early pregnancy: fetus is below pelvic brim, TAUS hard esp if thick abd adipose tissues
- cervical assessment: for measurement of cervical length (more accurate)
- placenta previa: esp if posteriorly located (difficult to visualize transabdominally), close to term (inform on mode of delivery)
TAUS: more appropriate if >12w gestation
Features to confirm pregnancy viability
Structures visualized in early gestation:
- gestational sac 4-5w, yolk sac ~5w, embryo 5-6w
- Viability of fetus: visible heartbeat from 6w onwards
Diagnosis of disorders of early pregnancy:
- missed miscarriage: empty gestational sac within a blighted ovum - blighted ovum: the gestational sac grow but the embryo does not
- ectopic pregnancy: no intrauterine sac, adnexal mass, POD fluid
Features for dating pregnancy
Dating of fetuses:
- Similar growth rate up to ~20w → allow dating by fetal size
- The earlier the measurement is made, the more accurate the prediction
- Crown-rump length (CRL): used up to 13+6w
- Head circumference (HC): from 14-20w
- Also used: biparietal diameter (BPD) and femur length (FL)
Features to assess fetal growth rate
Parameters used:
- abdominal circumference (AC)
- head circumference (HC)
- estimated fetal weight (EFW): from AC, HC, BPD, FL
Fetal growth restriction (FGR, IUGR) (胎兒生長受限):
- Small-for-gestational age (SGA): defined as EFW ≤10th percentile: can be pathological or non-pathological
- FGR/IUGR: fetus unable to achieve its genetically determined potential size (brain-sparing asym. small)
Constitutional small featus
- Cause
- Associated factors
- Risk
- Growth chart feature
Compare symmetrically small fetus vs asymmetrically small fetus
- Cause
- Associated risk
- Growth chart difference
Causes of IUGR
- Maternal, placental, fetal factors
Causes of macrosomia
Macrosomia:
Constitutionally large (LGA): HC + AC both follow upper centile line
usu seen in tall parents or Afro-Caribbean ancestry
Macrosomia: usu AC show accelerated growth upward crossing centile lines
usu seen in DM babies
Assessment of multiple pregnancies on ultrasound
Common features on USG suggestive of fetal abnormalities
Polyhydramnios vs Oligohydamnios
- Cause
- Associated consequences
Assessment of liquor volume on USG
Cardiotocogram
- Monitored metrics
Cardio-: one transducer on abdomen for monitoring of fetal heart rate
Tocogram: another transducer on abdomen (between fundus and umbilicus) for monitoring of maternal uterine contraction
- tension of maternal abdominal wall → related to intrauterine pressure
- only infer intrauterine pressure from frequency and duration, if need accurate monitoring of intrauterine pressure then require intrauterine pressure sensor (not shown to be beneficial)
Reading: 1 square (1cm) = 1 minute
Role of CTG in antepartum care
Role of CTG in antepartum care:
- To allow early detection of fetal distress (also known as non-stress test, i.e. NST)
- Timing: started 2w before any reasonable chance of extrauterine survival
- interval depend upon clinical situation and degree of fetal risk: as frequent as 2 or 3 times daily in acute events (APH, regular uterine contractions) or conditions that can change and deteriorate rapidly (PROM)
- otherwise fetus can be monitored at intervals ≤1w
Procedure for CTG/ NST
Procedure for NST:
- pt in left lateral wedged position
- tocography adjusted to 5-10mmHg, paper speed 1cm/min → obtain baseline tracing for ≥10min
- if no acceleration seen, ask pt to lie more lateral and stimulate the fetus with acoustic stimulator → should not be extended beyond a period of 40min
- if baseline variability difficult to interpret or suspected sinusoidal pattern → ↑paper speed to 3cm/min for 5min
- record on tracing if on drugs, coffee, tea or smoking
CTG interpretation
DR C BRAVADO
DR: define risk (high / low)
C: contractions
BRa: baseline rate, i.e. average HR within the last 10 min
V: variability, i.e. oscillations in heart rate around baseline HR
A: accelerations → abrupt increase in fetal HR of >15bpm for ≥15s
D: decelerations → abrupt decrease in fetal HR of >15bpm for ≥15s
O: overall impression → reassuring, suspicious, abnormal
CTG
- Assessment of define risk, contractions and baseline rate
CTG
- Assessment of variability
- Reasons for low variability
V: variability, i.e. oscillations in heart rate around baseline HR
- occur as a result of interaction between nervous system and chemoreceptors + baroreceptors of CVS system → reflect the integrity of ANS
- measured by calculating deviance of peaks and troughs from baseline HR - e.g. peaks ~10bpm above and troughs ~20bpm below baseline → variability 10-20bpm
reasons for ↓variability:
- fetal sleeping: should last ≤40min (commonest cause)
- fetal acidosis: due to hypoxia, esp if late decelerations are also present
- fetal tachycardia
- drugs: e.g. CNS depressants (opiates, BZDs), methyldopa, MgSO4
- prematurity: variability is reduced at <28w gestation - congenital heart abnormalities
CTG
- Fetal HR acceleration: definition
A: accelerations → abrupt increase in fetal HR of >15bpm for ≥15s
reflect activity of SNS, usu a/w fetal movements
- considered reassuring sign of good fetal health
- absence of accelerations with an otherwise normal CTG is of uncertain significance
CTG:
FHR deceleration definition
Types
D: decelerations
- abrupt decrease in fetal HR of >15bpm for ≥15s
- reflect hypoxic stress, in which fetal reduce HR to preserve myocardial oxygenation and perfusion because increase in respiration depth and rate is not possible
