Screening + Monitoring Pregnancy

Question 1

CTG: cardiotocography indications

Answer 1

Confidently used > 32 wks
Normal = reassuring, abnormal not always pathological
Mat indications: pre-eclampsia, DM, APH, prev c section)
Fetal indications: IUGR, prematurity, oligohydramnios, multip, breech
Intra partum: oxytocin, epidural, induction

Question 2

CTG interpretation

Answer 2

Baseline: 110-160
Sustained tachy= hypoxia, fetal distress, mat pyrexia, exog B agonists
Sustained brady= severe fetal distress, mat sedation, hypoxia, post maturity, hypotension

Question 3

10-14 wk USS

Answer 3

Date fetus using crown-rump length
EDD calculated from LMP retained unless USS differs by more than 1 wk
>14 wks bi parietal diameter/head circumference used instead

Question 4

EDD

Answer 4

40 wks after first day of LMP

IF cycle is 28 days and regular

Question 5

Reasons for 1st trimester USS -12wks

Answer 5

Establish viability
Detect multiple pregnancies and det chorionicity + amnioticity
Nuchal translucency test
Gross anatomical abnormalities

Question 6

Chorionic villus sampling

Answer 6

Transabdo/transcervical under US guidance, rh -ve req anti D
Result in 48hrs
Risk of miscarriage 1-2%
11-14 wks
Not performed before 9-11 wks as fetal limb abnormalities can occur
Inconclusive (placental mosaicism) -> amnio

Question 7

Nuchal translucency

Answer 7

11-14 wks during 1st trimester USS
Thickness of skin fold over neck of fetus measured
Risk determined by combining result with blood markers

Question 8

Rhesus status

Answer 8

Blood group established at booking
15% rhesus -ve
Rhesus +ve fetus + sensitising event = anti D antibodies
Risk is to subsequent rhesus +ve pregnancy
HDN was 1% prior to introduction of prophylaxis

Question 9

Rhesus prophylaxis

Answer 9

All rhesus -ve
500 IU anti D at 28wks
500 IU anti D at 34 wks
Regardless of sensitising events
Additional prophylaxis at sensitising events: 250 IU 20
No prophylaxis for threatened or spontaneous miscarriage

Question 10

Sensitising events (rhesus disease)

Answer 10

APH
Closed abdo injury
ECV
Invasive procedures e.g. Amniocentesis, CVS, shunt
Intrauterine death

Question 11

BHCG

Answer 11

Unlikely to visualise gestational sac on USS
Repeat BHCG should double in 48hr with continuing pregnancy
Repeat USS in one week

Question 12

Triple test

Answer 12

Used if too late for combined
+ve = >1/250
15-16 wks

Question 13

Amniocentesis

Answer 13

From 15 wks
Risk if miscarriage: 0.5-1%
Diagnostic test, antiD for rhesus -ve
Shed fetal cells extracted from amniotic fluid are analysed
Full karyotype 2-3 wks, PCR/FISH = more rapid

Question 14

Reasons for second trimester USS -20 wks

Answer 14

Approx 2/3 Down’s syndrome babies appear normal at 1st scan
Purpose = detect abnormalities in structural anatomy, measure fetal growth, measure liquor volume, site placenta rescan at 34 wks if near or over os
Can also determine sex with 99% accuracy

Question 15

Dating a pregnancy

Answer 15

EDD: from LMP
14 wks: bi parietal diameter
Discrepancy of > 14 days betw EDD derived from LMP and scan change to date indicated by scan
Accuracy of dating pregnacy decreases with gestation

Question 16

Reasons for additional follow up scans

Answer 16

Measuring small or large for dates in 3rd trimester: serial scans 2 wks apart to measure: abdo circ, bi parietal diam, femur length
Follow up of structural abnormalities identified at 20 wk scan
Amniotic fluid vol
Real time USS: fetal wellbeing
Fetal Echo: may congenital heart disease, prev children with congenital heart disease, some with epilepsy, DM
Uterine artery Doppler: those at increased risk of pre-eclampsia, abruption, growth restriction
To confirm breech

Question 17

Combined test

Answer 17

10-13 wks
Nuchal translucency 
PAPP-A
BetaHCG
2.2% false positive

Question 18

Quadruple test

Answer 18

Unconjugated oestradiol
Total HCG
AFP 
inhibin A
4.4% false positive

Question 19

Integrated test

Answer 19

Combined test
Quadruple test
1% false positive

Question 20

Infection tests at booking

Answer 20

Syphyilis
HIV
Hepatitis B
Rubella