Antenatal screening & diagnosis Flashcards
Ultrasounds in pregnancy
Booking scan at 10/12 weeks
Anomaly scan at 20 weeks
Monthly antenatal appointments until 28 weeks
Fortnightly antenatal appointments until 36 weeks
Weekly antenatal appointments until term
Booking Scan
Confirm intrauterine and viable
Check for twins and chorionicity
Exclude gross structural or uterine defects
Date pregnancy
Anomaly Scan
Significant structural defects
Locate placental site
>95% sensitive for significant anomalies
Down’s syndrome screening
Combined screening 11-14 weeks
Quadruple tests 14-22 weeks
Integrated or serum integrated tests
Combined screening test
Check for hCG, PAPP-A and nuchal translucency thickness
Given to all babies in first trimester
Quadruple test
Used to test patients who present too late for the combined test –> hCG, AFP, uE3, inhibin A
This is combined with the mother’s age to approximate the risk of Down’s syndrome
At this age NT ceases to be an effective measure
Integrated tests
A two stage test which combines serum protein markers with the NT (or not if serum)
Have two sets of tests –> must blind the results. Increased reliability if there is more serum tests
Down’s Risks
Low risk is defined as less than 1/150, while more than this is high risk
If high risk then Amniocentesis or CVS is offered past 15 weeks gestation
CVS (Chorionic villious sampling)
Ultrasound guided needle is pasted into the placenta to biopsy the chorionic villi
This can be done from 11-14 weeks and carries a 1% miscarriage risk - but rapid karyotyping
Amniocentesis
an US guided needle is used to sample the amniotic fluid around the baby and this can diagnose Down’s after 15 weeks
There is a 0.5-1% risk of miscarriage
Nuchal translucency (NT) thickness
Useful as a marker for significant defects.
the thicker the greater the chance of birth defect
3.5-4.4mm 86% chance of healthy birth
>6.5mm 31% chance of healthy birth
First trimester booking scan
An USS which is mainly to date and establish the pregnancy
Have a 90% detection rate for pregnancies
Uterine Artery Doppler
Measure the resistance into uterine artery and high resistance is linked strongly to IUGR, preterm labour etc
Looking for a saw tooth pattern, absent end diastolic flow is worrying, reversed end diastolic flow is super bad
Parameters checked at antenatal check
BP and urine (for protein and glucose)
abdominal auscultation
Assess fetal size (IUGR or Macrosomia) by USS or symphysio-fundal height
At risk pregnancies (8)
Hypertension or Pre-existing medical disorders
IUGR or macrosomia
Oligohydramnios or polyhydramnios
Multiple pregnancies or Antepartum haemorrhage
Number of ideal antenatal appointments
10 for nulliparous women
7 for multiparous women
More visits correlates to worse outcomes
Physical examination checked at antenatal visits
5 S’s
Shape –> ovoid, posterior position
Size –> symphysio-fundal height
Scars –> previous surgery or CSs
Striae –> sign of previous or present pregnancy
Signs of Fetal life –> movements or heart beat
Antenatal haematological checks
Booking –> FBC (Hb and platelets)
Group and save + Rhesus status
Infection screen (Rubella, syphilis, HIV, hepatitis)
28 weeks –> repeat FBC and group and save
36 weeks –> repeat FBC and group and save
Free fetal DNA testing
Started in late 90’s –> only available commercially but useful for screening for major trisomies, sex etc
Will replace other tests eventually
Nuchal Fold
Abnormal if over 6mm –> found 0.5% of fetuses
May be of no pathological significance
Choroid Plexus Cysts
2% of fetuses at 20 weeks –> 90% resolve at 26ws
A cyst over 2mm in one or both plexuses
Can be associated with trisomy 18 or 21 but usually of no pathological significant –> number, size or complexity not important
Intracardiac echogenic Foci
Rarely inductive of Aneuploidy in women below the age of 35.
Hyperechogenic Bowel
Bowel as bright as bone –>0.2-1.4% of 2nd trimester scans Subjective
Can be due to genetic abnormalities, congential infections or Intra-uterine haemorrhage or cystic fibrosis
Trisomy 21
Down’s syndrome
Holoprosencephaly
A spectrum of cerebral abnormalities resulting from incomplete cleavage of forebrain 1 in 1000 births
30% have karyotype abnormality - trisomy 13 & 18
Can be Lobar or alobar
Ventriculomegaly
1% of pregnancies at 20 week scan
Lateral ventricle diameter of 10mm or more
Aetiology–> genetic abnormalities, congential infections or Intra-uterine haemorrhage
When extreme lead to hydrocephalus
Dandy Walker Complex
Spectrum –> Loss of cerebellar vermis, cystic dilation of 4th ventricle and enlargement of cisterna magna (mega CM)
1 in 30,000 births –> Occurs in 13,18 and triploidy
Facial Defects
1 in 800 births –> only indicate trisomy 13 or 18 in 1-2% of cases .
unilateral or bilateral cleft lips most common
Congential Heart Disease
5-10 in 1,000 --> heterogenous aetiology Recognised association with trisomies: Present in --> 80-90% of 18 or 13 --> 40-45% of trisomy 21 --> 40% of turners
Congential Diaphragmatic Hernia
Herniation of abdominal viscera into the thorax
1 in 4000 births
In 50% of cases it indicates trisomy 13 or 18
Exomphalos
Saculated midgut outside the body due to failure of regression of midgut from umblical stock
1 in 4000 births
Likelihood of aneuploidy decreases with gestational age –> 50% at 12ws, 30% at mid gestation, 15% in neonates –> more likely in small exomphalos containing only bowel
Duodenal Atresia
1 in 5000 fetuses, –> indicates trisomy 21 in 40% of cases
Will see double bubble or polyhydramnios on USS
Hydrops
The accumulation of fluid in an abnormal fetal compartment –> either immune (rhesus) or aneuploidy (10-30%) –> can be Trisomy 21 or turners
Hydronephrosis
In most cases mild hydronephrosis will resolve spontaneously –> is dilated if over 4mm at 15-19wks, >5mm at 20-29wks, >7mm at 30-40wks
Trisomy 18
Edward syndrome
Trisomy 13
Patau syndrome
Turner’s Syndrome (lethal type)
Large nuchal cystic hygromata, oedema, pleural effusions, ascities, cardiac defects
Ultrasound signs of Trisomy 21
Mild ventriculomegaly Mild renal pelvis dilation
Nuchal edema shortening of limbs
Atrioventricular septal defect Echogenic bowel
Duodenal atresia Hypoplasia of mid phalanx of 5th finger (60%)
Ultrasound signs of Trisomy 18
Choroid plexus cysts Facial defects
Absent corpus callosum Nucheal edema
Dandy walker complex Heart defects
Diaphragatic hernia Esophageal atresia
Exomphalos Renal defects
Myelomeningocele Growth restriction
Overlapping fingers Talipes
Ultrasound signs of Trisomy 13
Holoprosencephaly Facial defects
Microcephaly Cardiac/renal defects
Exomphalos Postaxial polydactyly
Types of CHD in trisomy 21
AV canal –> 45%
VSD –> 35%
Isolated ASD 8%
Isolated Tetrology of fallot–> 7%
Turner’s syndrome (Non-lethal type)
Usually no USS abnormalities seen
USS abnormalities and chromosomal defects
Likelihood of chromosomal abnormalities increase with number of abnormalities detected.
Offer karyotyping if single large abnormality is found for if correctable defect is noted —> many abnormalities resolve and are found in normal pregnancies
Renal pelvic dilatation
Relative risk of Downs is 2, amnio is not needed in absence of other risk factors
Diagnosis of pregnancy
A gestational sac can be seen from 4 1/2 weeks transvaginally and 6 weeks Transabdominally
Gestational Sac
Not definate evidence of viable pregnancy - may be a delayed miscarriage (blighted ovum) - must see a fetal pole and heart beat
A pseduosac is a sign of ectopic pregnancy
Signs of a viable pregnancy
Regular sac, high in the uterus with rapidly increasing bHCG
A poor prognosis –> irregular sac, poor decidual reaction and abnormal yolk sac
Gestational age by USS
using a crown-rump length (CRL) - accurate to 5-7days - reliable up to 13wks
After this the spine curves and biparietal diameter should be used.
Types of Twins
Dizygotic 2/3, monozygotic 1/3
2% monochorionic monoamniotic or conjointed
Lambda sign–> Dichorionic,diamniotic but ‘T’ sign–> monochorionic, diamniotic
Complications of twins
monochorionic twins have a much higher mortality, TTTS, growth restriction, death of twin in utero.
should have 2-4 weekly scans to check
Therapeutic invasive procedures (6)
Intrauterine transfusion Pleural fluid aspiration Shunt insertion Bladder aspiration/shunt Amnioinfusion fetoscopy or laser ablation
How many antenatal appointments should a women have?
Nulliparous women –> 10
Multiparous women –> 7
Initial appointment with GP, booking appointment 8-12/40 and dating scan at 8-12/40, then 18-20/40 anomaly scan – subsequent appointments
Conditions requiring additional antenatal care
Current Conditions –> HTN, cardiac/renal/endocrine disease, psych or autoimmune conditions, severe asthma, malignancy
Previous pregnancies –> recurrent miscarriage, preterm birth, PE or HELLP, rhesus isoimmunisaion, previous uterine surgery
FGM in antenatal care
Examine for type to see if it will present an obstetric problem
Explain rules relating to performing FGM on the child
Mental health and antenatal care
Should specifically ask at booking, post natally at 4-6 weeks and 3-4 months (depression or psychosis)
Safeguarding in antenatal care
Make sure to be alert for the signs of abuse
Provide a sale environment so that the women feels able to disclose if she has any concerns
Haematology in antenatal care
Check for anaemia
Check for rhesus status, and screened for atypical red cell alloantibodies at the beginning and end of pregnancy
If women are at high risk screen for haemaglobinopathies
Infection screening in antenatal screening
Routinely we screen for: asymptomatic bacteruria,
Hep B, HIV, Rubella susceptibility and syphilis
Pregnancy related conditions which should be considered during care
Gestational diabetes
Pre-eclampsia
Gestational chloestasis
Raised maternal serum a-fetoprotein
Open neural tube defect
Ultrasound “banana” and/or “lemon” sign of cerebellum
Chiari II malformation and <24wks spina bifida
Alpha-Fetal Protein levels
Low levels indicate Downs but high levels indicate a break in the skin which may be due to spina bifida.
Timing of Twin division
Dizygotic - seperate eggs
Monozygotic dichorionic –> divide before 3days, monochorionic, diamnoitic –> between 4-7 days,
Monochorionic, monoamnitotic or conjointed –> after 7 days.
Basic downs risk by age
1/1,000 at 30 then divide by 3 for every 5yrs.
