Elevated Msafp
Roya Sohaey, MD
DIFFERENTIAL DIAGNOSIS
Common
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Open Neural Tube Defect
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Spina Bifida
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Exencephaly, Anencephaly
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Encephalocele
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Abdominal Wall Defect
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Gastroschisis
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Omphalocele
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Body Stalk Anomaly
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Multiple Gestations
Less Common
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Perigestational Hemorrhage
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Fetal Demise
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Placental Insufficiency
Rare but Important
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Maternal Tumors
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
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Alpha fetoprotein (AFP)
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Normally produced from several sources in developing fetus
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Yolk sac
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Fetal gastrointestinal tract
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Fetal liver
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Circulation of AFP
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Maternal serum alpha fetoprotein (MSAFP) test
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Drawn at 15-20 weeks menstrual age
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Part of genetic screening
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Screening for anomalies (spina bifida)
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Adjusted for maternal factors
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Weight
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± Diabetes
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Ethnicity
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MSAFP results
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Reported as multiples of the median (MOM)
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> 2-2.5 MOM considered positive screen
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Reasons for positive MSAFP screen results
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Incorrect menstrual dates (20%)
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Recalculate result after ultrasound
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Unsuspected multiple gestations
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Twin MSAFP = approximately twice singleton values
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Use of MSAFP screening in known multiple gestation is controversial
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Fetal anomalies
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Any anomaly with ↑ fetal internal organ exposure to amniotic fluid
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Placental abnormalities
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Primarily from fetal-placental hemorrhage
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Fetal levels 100,000 times > maternal
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Small hemorrhage easily causes ↑ MSAFP
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Helpful Clues for Common Diagnoses
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Open Neural Tube Defect
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Spina Bifida
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Bony vertebral defect + neural content exposure to amniotic fluid
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73% lumbar
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17% sacral
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9% thoracic
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1% cervical
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80% with overlying sac
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Almost all with Chiari II malformation of brain
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14% with aneuploidy
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Exencephaly, Anencephaly
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Absent calvarial vault
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Variable amount of supratentorial brain
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Brain exposed to amniotic fluid, which erodes neural tissue and leaves angiomatous stroma
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Face: Proptotic eyes, cleft lip/palate
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Encephalocele
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Herniation of intracranial structures through skull defect
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Occipital most common
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Parietal, vertex, frontal more rare
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Associations: Trisomy 13, trisomy 18, Meckel-Gruber syndrome
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Look carefully for other anomalies
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Abdominal Wall Defect
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Gastroschisis
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Bowel herniation through right paramedian defect
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Normal cord insertion
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No covering membrane
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Progressive bowel dilatation often seen
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Intrauterine growth restriction (IUGR) common in 3rd trimester
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Almost all with ↑ MSAFP
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Omphalocele
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Herniation of abdominal contents into base of umbilical cord
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Midline abdominal wall defect
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Most often involves liver
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Covering membrane present (difficult to see early, without ascites)
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70% with ↑ MSAFP (30% normal MSAFP)
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30% with aneuploidy
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Omphaloceles that contain only bowel more associated with aneuploidy
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Body Stalk Anomaly
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Fetal evisceration
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Visceral organs attached to placenta
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Short or absent umbilical cord
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No covering membrane
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Scoliosis is prominent feature
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Amniotic bands seen in 40%
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Other abdominal wall defect diagnoses
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Pentalogy of Cantrell
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OEIS syndrome
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Bladder/cloacal exstrophy
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Multiple Gestations
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Determine chorionicity/amnionicity
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Dichorionic diamniotic twins
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Most common type of twins
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2 placentae
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“Twin peak” if adjacent placentae
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Thick separating membrane
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Monochorionic diamniotic twins
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Single placenta
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No “twin peak” sign
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Thin separating membrane
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Twins are same gender
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Monochorionic monoamniotic twins
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Single placenta
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