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Obstetrics and Gynecology > Prenatal Screening, Diagnosis and Treatment > Flashcards

Prenatal Screening, Diagnosis and Treatment Flashcards

1
Q

define screening

A

allows high risk individuals to be selected out of a low risk population at risk for a given diagnosis or complication

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2
Q

how does prenatal diagnosis differ from prenatal screening

A

prenatal diagnosis is nearly always diagnostic and is usually far more specific than screening but amniocentesis and CVS (which are used for prenatal diagnosis) have greater risk of complications, including pregnancy loss

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3
Q

what is the genetic abnormality behind cystic fibrosis

A

autosomal recessive

results from abnormality in cystic fibrosis transmembrane conductance regulator (CFTR) which is the gene responsible for chloride channels

almost call CF patients have chronic lung disease because of recurrent infections leading to irreversible lung damage and strain on the right ventricle (cor pulmonale)

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4
Q

clinical manifestations of CF

A

almost call CF patients have chronic lung disease because of recurrent infections leading to irreversible lung damage and strain on the right ventricle (cor pulmonale)

85% of CF patients have pancreatic insufficiency manifested by chronic malabsorption and failure to thrive

life limiting: lung disease

median survival is close to 40 years for those more today in the USA

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5
Q

what is the genetic abnormality behind sickle cell anemia

A

autosomal recessive

single point mutation in gene for beta chain og HgB

resulting HbS forms polymers that when deoxygenated cause the cells to lose biconcave shape and become sickled

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6
Q

clinical picture of sickle cell anemia

A

hemolytic anemia due to sickled shape

shortened life expectant

frequent pain crises secondary to vaso-occlusion of small vessels by the dysmorphic erythrocytes

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7
Q

who should be screened for sickle cell anemia

A

more common among african americans–all should be screened in pregnancy

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8
Q

what is the heterozygote advantage of sickle cell trait

A

heterozygotes confer resistance to plasmodium vivax (malaria)

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9
Q

how do you screen for sickle cell anemia

A

hemoglobin electrophoresis which distinguishes HbS from HbA

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10
Q

genetic abnormality behind tay-sachs disease

A

autosomal recessive

most common in Eastern European Jews and french canadians

1/27-30 Ashkenazi Jews is a carrier for abnormal tay-sachs allele (so the incidence in this pop is 100x higher) –> possibly due to a founder effect

occurs due to deficiency of hex A which is responsible for degradation of GM2 gangliosides–> accumulation of gangliosides–> enlarged neurons–> cellular dysfunction–> neuronal death

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11
Q

clinical manifestation of tay-sachs

A

infants develop symptoms approx 3-10 months after birth

early sx–> loss of alertness, excessive reaction to noise (hyperacusis)

progressive developmental delay and neurologic degeneration in intellectual and neurologic function

myoclonic and akinetic seizures can present 1-3 months later

cherry red spot is seen on fundoscopic eye exam

eventually suffer from paralysis, blindness and dementia and typically die by age 4

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12
Q

what are the thalassemias

A

set of hereditary hemolytic anemias caused by mutations that result in the reduction in the synthesis of either alpha or beta chains

results in imbalance of globin chain synthesis and subsequently unpaired globin chains produce insoluble tetramers that precipitate in the cell and cause damage to membranes

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13
Q

in what populations is beta-thalassemia more common

A

mediterranean, asian, african

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14
Q

what does the most severe form (4 mutations) of alpha thalassemia cause

A

fetal hydrops

is incompatible with life

infants are delivered premature and are pale, hydropic, severely anemic and have splenomegaly

fetal hemoglobin electrophoresis reveals no HbF, no HbA and approximately 90-100% Hb Bart

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15
Q

how do you screen for alpha and beta thalamssemia

A

CBC

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16
Q

what is the only way to achieve a definitive diagnosis of aneuploidy

A

karyotype

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17
Q

what are the components of first trimester screening for aneuploidy

A

nuchal translucency combined with pregnancy-associated plasma protein A (PAPP-A) and beta hCG

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18
Q

what are the components of the second semester screen for aneuploidy

A

quad screen–> MSAFP estriol, beta hCG and inhibin

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19
Q

what does NIPT look at

A

looks for aneuploidy in cell free fetal DNA in maternal serum

  • not applicable in twins
  • can miss chromosomal mosaicism
  • do not currently assess all chromosomes as a karyotype does

BUT are highly sensitive and specific in women with high risk of aneuploidy

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20
Q

what is the most common cause of down syndrome

A

trisomy 21

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21
Q

describe the typical Down syndrome phenotype

A

short stature
classic facies
developmental delay
mental retardation with IQs ranging from 40 to as high as 90

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22
Q

what are the associated physical anomalies associated with Down syndrome

A

cardiac defects

duodenal atresia or stenosis

short limbs

*some of these can be seen by U/S but up to 40-50% of fetuses with Down syndrome will not have diagnosable anomalies by U/S, making U/S a poor screening tool

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23
Q

how do women undergo screening for Down syndrome

A

first trimester screen (nuchal translucency with PAPP-A and bhCG) and/or the quad screen (MSAFP, nCG, estriol and inhibin A) between 15-20 weeks gestation

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24
Q

what is the sensitivity for first trimester screening for down syndrome

A

82-87%

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25
Q

what is the sensitivity for quad screening for down syndrome

A

80% (alone)

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26
Q

what is the sensitivity of the combo of first trimester and quad screening for down syndrome

A

95% (with screen positive rate of 5%)

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27
Q

how sensitive is NIPT to detect down syndrome

A

98-99% or better

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28
Q

what are the common trisomies

A

13, 18, 21

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29
Q

what is another name for trisomy 18

A

Edward syndrome

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30
Q

what is the sensitivity of dual first trimester and quad screening for trisomy 18

A

90%

31
Q

what is the sensitivity of NIPT for trisomy 18

A

97%

32
Q

what is the effect of trisomy 18

A

lethal aneuploidy

nearly all neonates die in the first two years of life

associated with multiple congenital abnormalities which are typically seen on U/S (in 95% of cases)

33
Q

is U/S a reasonably screening tool for trisomy 18

A

yes–95%

34
Q

what are the physical signs suggestive of Edward syndrome

A

clenched fists

overlapping digits

rocker bottom feet

cardiac defects (VSD, tetralogy of fallot)

omphalocele

congenital diaphragmatic hernia

neural tube defects

choroid plexus cysts

35
Q

what is another name for trisomy 13

A

patau syndrome

36
Q

what is the ultimate effect of trisomy 13

A

lethal aneuploidy

85% will not live past 1 year

37
Q

what are the common abnormalities associated with trisomy 13

A

holoprosencephaly

cleft lip and palate

cystic hygroma

single nostril or absent nose

omphalocele

cardiac anomalies (hypoplastic left heart)

limb anomalies (clubfoot and clubhand, polydactyly, overlapping fingers)

38
Q

are the first trimester and quad screens good tools for trisomy 13 screening

A

no–outcomes are variable

however, anomalies are often visible on U/S

39
Q

define turner’s syndrome

A

45X karyotype

40
Q

define klinefelter syndrome

A

47, XXY karyotype

41
Q

describe the phenotype of turner’s syndrome

A

phenotypically female

short stature

primary amenorrhea

sexual infantilism

webbed neck

low set ears

low posterior hairline

epicanthal folds

wide carrying angle of arms

shield-like chest

wide set nipples

short fourth metacarpal

renal anomalies

lymphedema of extremities at birth

CV anomalies–>coarctation of the aorta

42
Q

what anomaly is seen on U/S in Turner’s

A

cystic hygroma

43
Q

is there a screening test for turners

A

no –might be available to diagnose through NIPT

44
Q

is there a screening test for Klinefelters

A

no

45
Q

common findings in klinefelters

A

small, firm testes with hyalinization of the seminiferous tubules

infertility

gynecomastia

mental retardation

elevated gonadotropin levels due to decreased levels or circulating androgens

46
Q

how many cells is a morula and when does this form

A

16 cells

day 4

47
Q

what developmental form implants into the uterus

A

blastocyst

48
Q

when does gastrulation occur

A

week 3

49
Q

what is the period of organigenesis

A

week 3-8 after conception–5-10 GA

50
Q

when does the neural tube form

A

begins day 22-23 after conception (week 4)

anterior neuropore (brain) closes by day 25

posterior neuropore (spinal cord) closes by day 27

closure of the neural tube coincides with formation of its vascular supply

majority of NTDs develop as a result of defective closure by week 4 of development (6 weeks GA)

51
Q

why do women take folic acid

A

to prevent NTDs

52
Q

what is the classic U/S finding in spina bifida

A

“lemon” sign–> concave frontal bones

“banana” sign–> cerebellum that is pulled caudally and flattened

ventriculomegaly and club feet are also seen

53
Q

what blood test screens for NTDs

A

MSAFP

an open neural tube leads to elevated amniotic fluid alpha-fetoprotein (AFP) that crosses into the maternal serum

54
Q

when does heart formation start

A

week 3 after conception

55
Q

describe Eisenmenger physiology

A

right ventricular hypertrophy

pulmonary HTN

right to left shunt

56
Q

what is tetralogy of fallot

A

VSD with an overriding aorta, pulmonary stenosis or atresia, RV hypertrophy

57
Q

what is Potter syndrome

A

renal failure leading to anhydramnios, which in turn causes pulmonary hypoplasia and contractures or deformations of the limbs in the fetus

it is a bilateral renal agenesis

58
Q

what does sensitivity of a test represent

A

the number of people are affected and test positive

59
Q

what does specificity of a test represent

A

the number of people who are unaffected and test negative

60
Q

what is the nuchal translucency test and what does it look for

A

good for aneuploidy–down syndrome in particular

measures the posterior feal neck taken in profile view

61
Q 
how are 
1. beta hCG
2. estriol
3. MSAFP
4. inhibin 
affected in trisomy 21
A
  1. decreased
  2. decreased
  3. elevated
  4. elevated
62
Q 
how are 
1. beta hCG
2. estriol
3. MSAFP
4. inhibin 
affected in trisomy 18
A

all decreased

63
Q 
how are 
1. beta hCG
2. estriol
3. MSAFP
4. inhibin 
affected in trisomy 13
A

depends on defects

64
Q

what does MSAFP screen for

A

NTDs

is higher in NTDs, lower in down syndrome

65
Q

what are other causes for elevated MSAFP (not NTDs)

A

inaccurate dating (increases with gestational age)

abdominal wall defects

multiple gestations

placental abnormalities

fetal demise

66
Q

what should you be aware of in a patient with elevated MSAFP without elevated amniotic AFP

A

greater risk o pregnancy complications associated with the placenta (abruption, preeclampsia, IUGR, IUFD)

67
Q

what might an echogenic intracardiac focus (EIF) suggest on U/S

A

down syndrome

is a calcification of the papillary muscle without an particular pathophysiology

not a very helpful test tho

68
Q

when can you get samples for NIPT

A

by 10 weeks

69
Q

when can you perform amniocentesis

A

after 15 weeks

early amniocentesis has higher risks for pregnancy loss

70
Q

how do you do amniocentesis

A

place a needle transabdominally through the uterus into the amniotic sac and withdraw some of the fluid

fluid contains sloughed fetal cells that can be cultured and karyotyped

cultures take 5-7 days to grow

FISH can be done to ID genetic problems

71
Q

common risks of amiocentesis

A

rupture of membranes

preterm labour

fetal injury (rare)

72
Q

what is CVS

A

chorionic villus sampling

can be used to obtain karyotype sooner than amniocentesis because performed at 9-12 weeks

place a catheter into intrauterine cavity, either transabdominally or transvaginally, and aspirate small quantity of chorionic villi from placenta

73
Q

what is the risk of complications from CVS

A

higher than amniocentesis

can be confused in cases of placental mosaicism

preterm labour

premature ROM

previable delivery

fetal injury

74
Q

why dont we do CVS before 9 weeks

A

assoc with limb injury secondary to vascular interruption

Obstetrics and Gynecology (21 decks)

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