| Maternal serum alph1a-fetoprotein screening |
MSAFP |
Alpha-fetoprotein (AFP) is a major protein produced by the fetal yolk sac, liver, and gastrointestinal tract. Maternal serum AFP
(MSAFP) is measured at 15-20 weeks gestation (optimally at 16-18 weeks) to screen for fetal anomalies. MSAFP is used primarily to
screen for open neural tube defects. Increased levels are also .associated with fetal abdominal wall defects (eg, gastroschisis,
omphalocele) and multiple gestation Less commonly, an increased MSAFP can be seen in fetal congenital nephrosis and benign
obstructive uropathy.
An elevated MSAFP warrants careful ultrasound evaluation of the fetal anatomy. In addition, the number of fetuses should be
clarified as multiple gestations produce more AFP. Gestational age is also confirmed as interpretation of AFP level depends on an
accurate gestational age
(Choice A) Cystic fibrosis results most commonly from ll.F508 mutation. If both parents are carriers of the genetic mutation, fetal
diagnosis can be made by chorionic villus sampling, amniocentesis, or fetal blood sampling. Cystic fibrosis does not affect AFP
levels.
(Choice C) Most major fetal cardiac anomalies can be diagnosed by a screening second-trimester ultrasound. Congenital heart
disease does not affect AFP levels.
(Choice D) Elevated levels of AFP can be seen in patients with hepatocellular carcinoma, tumors of gonadal origin, and liver disease
(eg, acute or chronic viral hepatitis} It is very unlikely that this patient has any of these as she has no symptoms.
(Choices E and G) Down syndrome can be caused by meiotic nondisjunction or Robertsonian translocation. Trisomy 18 is usually
caused by meiotic nondisjunction. Down syndrome has a profile ,of low MSAFP, low estriol, elevated 13-HCG, and an increased inhibin
A level. Trisomy 18 has low MSAFP, very low estriol, very low 13-HCG, and normal inhibin A level. This patient had an elevated, not
low, AFP, so trisomy is unlikely.
(Choice F) Multiple gestation is an unlikely cause of increased MSAFP in this patient because the uterine size is consistent with her
reliable dates and an early pelvic examination. This patient is also relatively slender so the evaluation of fundal height is more
accurate than in an obese patient
Educational objective:
Elevated maternal serum a-fetoprotein is seen in fetal abnormalities such as open neural tube defects, gastroschisis, and
omphalocele. It is also elevated in a multiple-gestation pregnancy. An ultrasound should be performed to evaluate the fetal anatomy.
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