Genetics: Prenatal Dx and Dev Genetics

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created 6 years ago by jgaversa5
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1

what are the indications for prenatal diagnostic tests

older mom
fhx of genetic/birth disorder
increased NTD risk
abnormal US or maternal serum screen

2

what are the phases of prenatal dx

ID at risk
risk assessment
discuss diagnostics and testing available

3

what are the noninvasive methods of prenatal screening

MSAFP
triple/quad screen
US

4

what will the MSAFP show

ONTDs possible

5

when can US be done for prenatal screen

first and second trimesters

6

what are the invasive prenatal dx screening tests

amniocentesis
CVS (chorionic villus sampling)
PUBS (percutaneous umbilical blood sampling)/cordocentesis

7

what are the main things detected by maternal serum screening

ONTDs and chromosomal aneuploidies

8

is maternal serum screen diagnostic

no

9

what is the goal of maternal serum screen

ID patients with increased risk of fetal disorder and offer diagnostic tests to them

10

when do the problems assd with NTDs take place

week 3-4 of fetal embryonic development

11

what are the types of NTD

anencephaly, encephalocele, spina bifida

12

what does NTD severity/prognosis depend on

location and extent of lesion

13

what can NTDs cause

paralysis, incontinence, developmental delay

14

what are ONTDs usually a result of

multifactorial inheritance

15

what decreases risk for NTDs

folic acid supplementation

16

how much folic acid should all women take every day

0.4 mg

17

how much folic acid should women with prior affected pregnancy take per day

4 mg

18

what does an increased MSAFP indicate

increased risk for ONTD

19

is a more open or more closed defect more sensitive to MSAFP detection

more open

20

will MSAFP detect closed NTDs

no

21

when is MSAFP most accurate

weeks 16-18

22

what is MSAFP influenced by

gestational age
maternal weight
race
diabetic status
multiple gestation

23

what are the cutoffs for MSAFP normal range

2-2.5 multiples of the mean

24

what is the maternal serum screen of second trimester

triple screen: MSAFP, uE3, HCG

25

what is the maternal serum screen of first trimester

quad screen: MSAFP, uE3, HCG, Nuchal thickness

26

when is ultrasound used as a screen

1st and 2nd trimester

27

what is uE3

unconjugated estradiol

28

what is the maternal serum screen for down's

AFP, HCG, uE3, maternal age

29

how do detection and false positive rate differ for the down syndrome maternal serum screen

any given maternal age

30

what is the cutoff generally for maternal serum screen

1/270

31

what are the lab values generally for maternal serum down syndrome screen

increased HCG, low uE3, low AFP

32

what are the lab values generally for maternal serum screen for trisomy 18

HCG, uE3, AFP all low

33

how do labs generally screen for maternal serum screen

risk based assessment

34

what is the risk cutoff for trisomy 18 assessment

1/100

35

when is the quad screen done

first trimester, 9-13 weeks gestation

36

how is the 9-13 weeks gestation determined for validity of quad screen

blood spot

37

what is the quad screen

triple screen (HCG, uE3, MSAFP)+PAPP-A (pregnancy-assd plasma protein A)

38

what does the quad screen generally assess risk for

Down's and trisomy 18

39

what is another quad screen that can be used to detect potential Down and T18?

PAPP-A+free beta HCG, maternal age+ clinical data

40

is the detection validity generally higher for T18 or downs in terms of the quad screen

T18

41

what indicates an increased risk for downs in quad screen

increased free beta HCG, decreased PAPP-A

42

what indicates an increased risk for T18 in quad screen

decreased free beta HCG and decreased PAPP-A

43

how is modified risk assessed in quad screen

comparatively to patient's age related risk and lab's cutoff risks

44

what is the modified first trimester quad screen

first semester maternal serum screen with the option of nuchal translucency measurement through sonar

45

what can the modified first trimester quad screen evaluate

T21 and T18 risk assesement

46

what is nuchal translucency

association between thickened NT and increased risk for chromosomal abnormalities

47

what is the general range of nuchal translucency

over 2 mm-10 mm

48

when can the nuchal translucency screen be done

10 weeks and 4 days to 13 weeks and 6 days

49

what in addition to the nuchal translucency measurement is delivered to the lab at the same time

blood spot card

50

when using the quad screen, are detection and false positive rates better for T18 or down's

T18

51

with the exception of chromosomal abnormalities, are most increased nuchal translucencies born free of defect

yes

52

what are the increased terminal risks for increased NT babies

miscarriage an perinatal death

53

what are the increased particular defects for increased NT babies

cardiac defects, diaphragmatic hernia, others

54

are genetic syndromes common in increased NT babies

yes

55

what is recommended for incresased NT babies

extensive sonar and fetal echo

56

is US diagnostic for fetal abnormalities

no

57

can risk change for US screening for fetal abnormalities

yes

58

does a normal US rule out chromosomal abnormalities

no

59

what is the US screen particularly good for

major congenital abnormalities

60

does US detect ONTDs well

yes, high sensitivity

61

what are the assd US findings for ONTDs

lemon sign and banana sign

62

will ONTDs present in US right away with hydrocephalus

most will get them, but might not appear until later

63

what are the chromosomal disorders with assd US findings

T21, 18, 13
45X
triploidy
unbalanced chromosomes

64

what are the visceral structural US findings in downs syndrome

heart and duodenal abnormalities

65

what are the markers of US findings in downs

nuchal thickness increased
echogenic bowel
short humerus or femur
renal pyelectasis
shortened middle finger, sandal gap, absetn nasal bone

66

what are the US findings in T13

holoprosencephly with assd cleft lip and palate
polydactyly
heart
IUGR
omphalocele
urogenital abnormalities
NTD

67

what are the US findings in Turner's

cystic hygroma
non immune hydrops
heart abnormalities
horseshoe kidney, renal abnorm

68

what is diagnostic US used for

structural detection
congenital heart defects and NTDs

69

what is so good about US

no disruption of fetal envirnoment

70

what isn't so good about US

doesn't get everything

71

what do you do in prenatal diagnosis once an abnormality is found

diagnostic procedure is applied to corroborate

72

what are some acceptable prenatal dianostics that can be used once an abnormality is detected

amniocentesis, CVS, PUBS, fetoscopy, embryoscopy

73

what is amniocentesis

amniotic fluid sample with fetal cells transabdoimnally by syringe

74

when is amniocentesis done

15-16 weeks after first day of last menstrual period but can be as early as 11 weeks

75

what is amniocentesis good for

assaying AFP for ONTDs

76

what is AFP and where is it mostly made

fetal glycoprotein made mainly in the liver

77

why can AFP be detected by amniocentesis

secreted into fetal ciruclation, excreted through amniotic fluid via fetal urine

78

how does AFP enter maternal blood stream

placenta

79

how can AFP be sampled besides amniocetessi

MS-AFP

80

what are the risks of amniocentesis

uterine cramping
transient spotting
leakage of fluid
miscarriage
infection (rare)

81

what is chorionic villus sampling

remove small amount of chorionic tissue (tertiary villi derived from trophoblast)

82

how will the villi be biopsied in CVS

transcervically or transabdominally

83

when is CVS done

weeks 11-12

84

what is good about CVS

results available at early stage (can't even get AFP this early)

85

what are the risks of CVS

higher micarriage rate than amniocentesis
uterine cramping/vaginal bleeding
higher infection risk than amniocentesis
limb abnormalities (rare after week 10)
blood group sensitization

86

what are the contraindications of CVS

STD
anatomical factors: uterus shape or placental location

87

what is PUBS/cordocentesis

sample of fetal blood directly from umbilical cord with US guidance

88

when is PUBS/cordocenteis used

US follow up with fetal abnormality

when culture of amniotic fluid cells has failed or yielded ambiguous reults

DNA diagnosis of a disorder requires biochemical test of fetal plasma or blood cells

89

when is PUBs/cordocentesis done

weeks 19-21

90

what are the main risks of PUBS/cordocentesis

fetal loss risk 2-3%
hemorrhage risk

91

is cffDNA invasive or not

no

92

where does cffDNA orginate from

placental cells

93

how much DNA does cffDNA constitute of the female

2-6% DNA in maternal ciruclation

94

are the cffDNA fragments large or small

short

95

when is cffDNA detectable

week4

96

when is cffDNA gone

2 hours after birth

97

how can cffDNA be detected

fetal DNA is expected to have sequences different form mom and also sequences that differ in methylation patterns

98

what are the clinical uses of cffDNA

fetal sex determination (X linked recessive disorders)
Rh dz
detetion of fetal aneuoploidy
monogenic disorders

99

what is cffDNA most accurate in clinical use

detetion of T21>T18 and T13

100

what must be done with cffDNA positives of Trisomies

confirm with invasive testing