Screening for fetal defects

Maternal serum and amniotic fluid AFP are useful tests for detecting some serious fetal anomalies. Maternal serum AFP is elevated in 85% to 95% of cases of fetal open neural tube defect and is low in about 30% of cases of fetal Down syn-drome. Because maternal serum screening for fetal... 

Nicolaides KH, Azar G, Byrne D, Mansur C, Marks K. Fetal nuchal translucency ultrasound screening for chromosomal defects in first trimester of pregnancy. BMJ 1992 304 867-9. 

L4. Leighton, P. C., Gordon, Y. B., Kitau, M. J., Leek, A. E., and Chard, T., Levels of alpha-fetoprotein in maternal blood as a screening test for fetal neural-tube defect. Lancet 2, 1012-1015 (1975). 

Determination of AFP levels in amnio tic fluid or maternal serum is used for antenatal screening for certain birth defects and chromosomal abnormafities in the fetus (see Chapter 54). Elevated maternal serum AFP indicates the possibility of a neural tube or open abdominal wall defect in the fetus. The levels may also be elevated with multiple fetuses, low birth weight, fetal demise, and incorrect estimation of gestational age. Trisomy 21 (Down syndrome) and trisomy 18 are associated with low maternal serum AFP levels. AFP is also used as a marker for hepatocellular and germ cell carcinomas. For a discussion of the role of AFP as a tumor marker, see Chapter 23. 

Any disruption in the biosynthetic pathway will lead to very low maternal serum UE3. Conditions that cause disruption include fetal anencephaly, placental sulfatase deficiency, fetal death, chromosome abnormalities, molar pregnancy, and Smith-Lemlit Opitz syndrome (SLOS). Placental sulfatase deficiency presents in the infant as X-linked ichthyosis. It is present in approximately 1 in every 2000 males. Because of the lack of uEj, the mother often has delayed onset of labor. The cesarean section rate is significantly higher in these mothers. SLOS is a serious, rare birth defect that is the result of an inborn error in cholesterol metabolism, 7-dehydrosterol-7-reductase deficiency. Down syndrome leads to a modest decrease in uEj. Screening for Down syndrome is now the most common application of uEs measurements. ... 

Prenatal monitoring suggested maternal serum a-fetoprotein screening for neural tube defects before the twentieth week of gestation and high-resolution ultrasound at 16-1 8 weeks gestation to detect cardiac abnormalities fetal echocardiography is recommended if lithium is... 

Open neural tube defects, Down syndrome, and trisomy 18 (discussed separately below) are fetal anomalies that are partially detectable by maternal serum screening. However, because of the large number of pregnancies screened, and the interest in other fetal conditions and their possible association with abnormal maternal serum analyte concentrations, a wealth of associations between rarer conditions and screening results has been pubhshed. These findings are never diagnostic and are reported rarely by the screening laboratory. In certain circumstances, however, the healthcare provider may determine a need for more extensive medical evaluation. 

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