Routine assessment of amniotic fluid alpha-Fetoprotein in early second-trimester amniocentesis is no longer justified

Open fetal neural tube defects are often followed by an increase in alpha-Fetoprotein concentration in amniotic fluid. For over 25 years there has been a routine to measure amniotic fluid alpha-Fetoprotein in conjunction with early genetic amniocentesis. The efficacy of such a screening test in a low-risk population has been questioned but never evaluated in a Swedish population.

Data were reviewed retrospectively from all consecutive early second-trimester genetic amniocenteses from two hospitals during the years 1993-2003. Indications for the genetic amniocenteses were maternal age > or = 35 years, maternal anxiety or a history of fetal aneuploidy. A questionnaire was sent to all obstetric clinics in Sweden regarding current common policy and experience of routine amniotic fluid alpha-Fetoprotein measurements, in the detection of open fetal neural tube defects.

A total of 1,813 samples were included. In eight cases (0.4%) the amniotic fluid alpha-Fetoprotein concentrations were > or = 3 multiples of median, but five of them were false positive (63%). Out of the three true positive cases, one had clinical relevance. In the other two cases the detection of open fetal neural tube defects was of subordinate importance. In Sweden, during 2004, 91% of the obstetric clinics performed routine assessment of amniotic fluid alpha-Fetoprotein at second-trimester genetic amniocentesis, but only 9% regarded the analysis useful in clinical practice.

According to our results, routine measurement of amniotic fluid alpha-Fetoprotein in early second-trimester genetic amniocentesis, to rule out a risk of open fetal neural tube defects, does not seem justified. The clinical usefulness seems to be limited.