Obstetrics - Ultrasound exam, CTG, Doppler flow studies, Biophysical profile, Pre-natal diagnosis

Question 1

Assessments done in early pregnancy scan

Answer 1

Question 2

Assessment of anomaly scan

Answer 2

Question 3

Assessments in 3rd trimester scan

Answer 3

Question 4

Indications of extra ultrasound scans during pregnancy

Answer 4

Question 5

Compare use of TVUS vs TAUS during pregnancy

Answer 5

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

Question 6

Features to confirm pregnancy viability

Answer 6

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

Question 7

Features for dating pregnancy

Answer 7

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)

Question 8

Features to assess fetal growth rate

Answer 8

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)

Question 9

Constitutional small featus

• Cause
• Associated factors
• Risk
• Growth chart feature

Answer 9

Question 10

Compare symmetrically small fetus vs asymmetrically small fetus

• Cause
• Associated risk
• Growth chart difference

Answer 10

Question 11

Causes of IUGR

• Maternal, placental, fetal factors

Answer 11

Question 12

Causes of macrosomia

Answer 12

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

Question 13

Assessment of multiple pregnancies on ultrasound

Answer 13

Question 14

Common features on USG suggestive of fetal abnormalities

Answer 14

Question 15

Polyhydramnios vs Oligohydamnios
- Cause
- Associated consequences

Answer 15

Question 16

Assessment of liquor volume on USG

Answer 16

Question 17

Cardiotocogram

• Monitored metrics

Answer 17

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

Question 18

Role of CTG in antepartum care

Answer 18

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

Question 19

Procedure for CTG/ NST

Answer 19

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

Question 19

CTG interpretation

Answer 19

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

Question 19

CTG

• Assessment of define risk, contractions and baseline rate

Answer 19

Question 19

CTG

• Assessment of variability
• Reasons for low variability

Answer 19

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

Question 20

CTG

• Fetal HR acceleration: definition

Answer 20

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

Question 21

CTG:

FHR deceleration definition
Types

Answer 21

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

Question 22

CTG Signal ambiguity

Definition
Suspicious features
Management

Answer 22

Signal ambiguity:

Definition: electrical monitor mistakenly detect maternal heart rate (MHR) instead of FHR
reason: faulty Doppler placement, inability of CTG to differentiate

Suspicious features:
- FHR running in low normal range
- FHR accelerations noted with >50% of contraction (esp when mother is pushing)
- apparent FHR declaration to MHR range that does not recover ± signal break in between (as distinct discontinuity)
- difference between maternal/fetal pulse <15bpm

Management:
- locate fetal heart by bedside US (recommended as can r/o IUD)
- relocate CTG sensor until another heart rate (i.e. FHR) is located which is ≥15bpm different from MHR
- place fetal scalp electrode (FSE) if possible

Question 23

Doppler flow studies

• Function
• Measurements

Answer 23

Question 24

Fetal vessel doppler flow study

Role
Abnormal findings

Answer 24

Question 25

Biophysical profile
- Indications
- Assessed metrics

Answer 25

Biophysical profile (BPP):
Indication: for antepartum fetal surveillance in pregnancies at ↑risk of antepartum fetal demise
- maternal ds: APLS, DM, HT, renal ds, SLE, cyanotic heart ds, Hb abnormalities
- prev pregnancy: fetal demise
- current pregnancy: ↓fetal movement (DFM), abnormal AFV, IUGR, isoimmunization, multiple gestation with growth discordancy, post-term

BPP = BATMAN Breathing, AFV, Tone, Movement and NST

Question 26

Confounding factors of biophysical factors

Answer 26

Normal biophysical activity is presumptive evidence that these regulatory centers are intact

However, absence of these activities may be due to non-pathologic reasons, e.g. deep sleep, transplacental passage of drugs that cause general suppression of brain (e.g. BDZs, opiates)

Sensitivity to hypoxia for centers: cardioregulatory > fetal breathing movements > fetal movement > fetal tone

For AFV, fetal hypoxia divert CO away from kidneys → oliguria → oligohydramnios (least sensitive to hypoxia)

Question 27

Biophysical profile

• Components
• Interpretation

Answer 27