Fetal anomaly scan potentially will replace routine AFAFP assays for the detection of neural tube defects.

OBJECTIVES

Introduction of the second-trimester fetal anomaly scan and the decision to offer this scan to every woman in the 18th-22nd week of pregnancy necessitates a re-evaluation of the diagnostic value of the measurement of alpha-fetoprotein (AFP) concentrations in the amniotic fluid (AF) for the detection of neural tube defects (NTDs).

METHODS

In this study of 6501 women who underwent amniocentesis, amniotic fluid AFP (AFAFP) concentrations were measured. The women were divided into three categories: group I, without any increased risk of fetal NTD (N = 6188); group II, with an increased risk of fetal NTD (N = 258); and group III, with a clinically diagnosed fetal NTD with known AFAFP concentrations (N = 55).

RESULTS

In 27 women of group I (0.4%), the MoM (multiple of the median) level was > 2.5 times the median AFP concentration for the corresponding gestational age, and in two fetuses this was related to NTD. In two pregnancies of group II (0.8%), an increased AFAFP was related to NTD. In group III, 44 of the 55 (80%) samples had an increased AFAFP.

CONCLUSION

In the near future, it is likely that imaging will replace AFAFP assays for the detection of fetal NTDs because high quality ultrasound imaging will detect NTDs accurately.