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Prenatal Diagnosis of Congenital Malformations. Max Brinsmead PhD FRANZCOG January 2010. 3 categories of congenital disorder. Some 1- 2% of babies will have a major disability that dates from the prenatal period Either Chromosomal disorder e.g. Down syndrome

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prenatal diagnosis of congenital malformations

Prenatal Diagnosis of Congenital Malformations

Max Brinsmead PhD FRANZCOG

January 2010

3 categories of congenital disorder
3 categories of congenital disorder
  • Some 1- 2% of babies will have a major disability that dates from the prenatal period
  • Either
      • Chromosomal disorder e.g. Down syndrome
      • Structural abnormality e.g. “Hole in the Heart”
      • Other e.g. Cerebral palsy
  • While a good deal of antenatal care in the 21st century is directed to the prenatal detection of these problems....
  • It is worth remembering that, for most, termination of the pregnancy is the only option
what can be detected in utero
What can be detected in utero?
  • All chromosomal abnormalities
  • About half of the major structural abnormalities
      • May be difficult in the 1st half of pregnancy
      • And varies with the resources available
  • Very few of the patients with cerebral palsy
types of tests
Types of Tests
  • Diagnostic tests
      • Have a high degree of accuracy
      • e.g. Amniocentesis for chromosomes
      • May be invasive, carry risk and expensive
  • Screening tests
      • Cheap and safe tests suitable for whole population
      • Selects a subgroup for diagnostic testing
      • So sensitivity and positive predictive value is important
  • Ultrasound can be used for both screening and diagnosis
      • Limited only by the resources available
two practical characteristics of a screening test
Two Practical Characteristics of a Screening Test
  • Sensitivity
      • The number of patients selected by the test as positive as a proportion of the total number of patients with the condition sought
      • e.g. A DRA test that identifies 3 out of 4 mothers with a Down syndrome baby has a sensitivity of 75% and will therefore miss 25% of the babies with this problem
  • Positive Predictive Value (PPV)
      • The likelihood that a patient identified by the test has the condition sought
      • e.g. A DRA with PPV of 10% means that 90% of women selected to undergo amniocentesis will NOT have this condition
markers for down syndrome
Markers for Down Syndrome
  • Ultrasound
      • Nuchal translucency (NT) ↑with DS
      • Nasal bone (absent with DS)
  • Maternal Serum
      • PAPP-A ↓with DS
      • Beta HCG ↑with DS
      • AFP ↓with DS and ↑with NTDs
      • Oestriol ↓with DS
      • Inhibin-A (useful in 2nd trimester testing)
down syndrome screening tests
Down Syndrome screening tests
  • Use the combined test (i.e NT measure, beta-HCG & PAPP-A )for patients who present in the first trimester
      • Sensitivity when optimally timed is 85-88%
      • Can help many patients avoid amnio & CVS
  • Use the Triple Test (i.e. beta-HCG, E3 and AFP) for patients who present in the 2nd trimester
      • Sensitivity when optimally timed is 65 – 75%
      • Also screens for NTDs
  • Integrated testing offers greater sensitivity and higher PPV but results are late
information required for the interpretation of tests
Information required for the interpretation of tests
  • Gestational age with accuracy
      • And this is why ultrasound c NT is so useful
  • Maternal age
      • Advancing age will increase the chance of a +ve result
  • Maternal ethnicity and weight
  • Multiple pregnancy?
  • Assisted conception?
  • Maternal diabetes?
  • Maternal smoking?
timing is all important
Timing is all important
  • Firstly it is desirable to make a diagnosis before 14w so that TOP is simple and safe
  • 1st blood test between 9 – 13w&6d
      • Optimally 10 -12 w
  • NT measure at 11 – 13w&6d
      • Optimally at 11.5 – 13.5w
  • Second trimester blood test 14 – 20w
      • Optimally 14 – 18w
  • CVS can be performed any time after 9.5w
  • Amniocentesis after 15w
timing is all important1
Timing is all important
  • Full chromosomal analysis from CVS or amnio takes 10 – 14d
  • Culture failure occurs in <0.5%
  • Colony mosaicism can be a problem
  • Some abnormalities can pose dilemmas
      • e.g. 47 XYY, 47XXY, 45XO
  • Fast FISH or DNA tests can be done overnight
  • But are much more expensive
  • And have a small risk of error
some myths surrounding pnd
Some myths surrounding PND
  • Most Down Syndrome babies are born to women over the age of 35
  • Because my other pregnancies and babies were normal I do not need testing
  • There is no Family History of Downs so I do not need testing
  • Husband’s age is important
  • The chance of aneuploidy after a positive screen test is equivalent to the risk calculated
amniocentesis and cvs
Amniocentesis and CVS
  • Practitioners of both state that the increased loss associated with both is about 1:100
  • Large studies say 0.5% for amnio and 1-2% for CVS
  • Most pregnancy losses occur within 7 – 10d
  • A few patients leak liquor after amnio
  • CVS is done PA for an anterior placenta and PV for a posterior placenta
  • Both procedures require US guidance
  • And are best done by practitioners of >50/yr
issues a patient needs to understand before undergoing a test
Issues a patient needs to understand before undergoing a test
  • What the test is for
  • And what it will not detect
  • What is their risk of the condition
  • What is the likelihood that the test will be positive
  • What are the sensitivity and PPV of the test
  • What will they do if the test is positive
  • What are the risks associated with further testing. What will that test reveal
  • What will they do if their baby is affected
so patient counselling is important
So Patient Counselling is Important
  • Pre test counselling will help to reduce post positive test anxiety
  • Resources are required for the optimal management of screen-positive patients
  • And the continuing care of patients who are screen-positive but amnio/CVS normal
  • Because they do have pregnancies at increased risk
      • Consultation with a MFM specialist may be desirable
increased nuchal translucency
Increased Nuchal Translucency
  • When aneuploidy has been excluded...
      • Risk of miscarriage <20w is 1.3% for NT 95 – 99th centile
      • But is 20% when NT >6.5 mm
  • Look for cardiac abnormalities
      • 1.7% if NT is 2.5 – 3.4 mm
      • 7.5% if NT >3.5 mm
  • Is it Cystic Hygroma? i.e. generalised oedema
      • 5-fold increased risk of aneuploidy
      • 12-fold increased risk of cardiac problem
      • 6-fold increased risk of perinatal death
      • So monitor – consult MFM if it does not resolve
low papp a
Low PAPP-A
  • When beta-HCG is high exclude Downs
      • (Trisomy 13 & 18 associated with low beta HCG)
  • When aneuploidy is excluded....
      • Monitor for early onset pre eclampsia & IUGR
      • ? Consult with MFM especially if beta HCG is high
  • Unexplained elevation of PAPP-A
        • “Not associated with any known pregnancy problem”
raised afp
Raised AFP
  • Causes include:
      • Wrong dates
      • Pregnancy bleeding
      • Multiple pregnancy
      • Open neural tube defects*
      • Anterior abdominal wall defects
      • Some rare tumours
  • So refer for tertiary level scanning
  • and
  • “Watch carefully” for the rest of the pregnancy
low oestriol in the 2 nd trimester
Low oestriol in the 2nd Trimester
  • Think about:
    • Placental sulfatase deficiency
        • X-linked recessive
        • Ichthyosis (lizard-like skin)
        • Mild corneal opacification
        • Cryptorchidism
      • Smith Lemli-Opitz Syndrome (rare 1:50,000)
        • Multiple malformtions
        • Mental retardation
        • Syndactly
    • So consider amniocentesis or CVS