SCREENING FOR NEURAL TUBE DEFECTS

• Done at 16-18 weeks.
• Levels are expressed as ng/ml and plotted against the normal distribution of the protein and reported as MOM (multiples of the mean).
• Upper limit of normal = 2 MOM Sensitivity = 85%.
• Abnormal level = 2.5 MOM. Sensitivity = 80%.
• Curves depend on:
• Accurate determination of fetal gestational age.
• Maternal weight and race.
• Significantly lower levels in patients with insulin dependent diabetes mellitus.
• Levels are higher with multiple gestations (tables for twin pregnancies have been reported but not for triplets).

PROTOCOL FOR OPEN NEURAL DEFECTS SCREENING

· For patients with an initial elevated AFP who have gestational age > 19 weeks, a second blood test is not recommended.  Instead these patients should proceed directly to a Level II Ultrasound.

· AF-AFP – amniotic fluid alpha fetoprotein.

· AchE – acetylcholine esterase.

AFP Level
Free Beta Level		Low	Within Normative Range	High
	Low	Trisomy 18 Fetal Demise Chromosomal Abnormalities Perinatal  Complications*		ONTD VWD GA Incorrect Perinatal  Complications*
	Within Normative Range		Low Risk	ONTD VWD Perinatal  Complications*
	High	Down Syndrome Chromosomal Abnormalities GA Incorrect Perinatal  Complications*		ONTD VWD Twins Perinatal  Complications*

* Perinatal Complications include impending fetal death, low birth weight and premature delivery.