Impact on spina bifida screening of shifting prenatal Down syndrome maternal serum screening from the second trimester to the first.

Objectives: Shifting screening for trisomy 21 to the first trimester has resulted in the loss of maternal serum alpha-fetoprotein screening for spina bifida. The aim of this study was to study the impact on open spina bifida prenatal screening.

Study Design: We reviewed prenatally diagnosed cases of spina bifida over three years: 2009 (only second-trimester screening, MSM2T), 2010 (transient period) and 2011 (majority first-trimester screening, MSM1T). Cases were assigned to three groups based on maternal serum markers (MSM2T, MSM1T and 'not performed'). Gestational age at diagnosis of spina bifida was compared between these three groups and between the years 2009 and 2011.

Results: Median gestational ages at diagnosis of the 742 spina bifida cases between the three groups were 22 weeks [18 -23], 22  weeks [21 -23] and 21  weeks [14 -23], respectively (P < 0.005). The diagnosis was made at 14-20 weeks in 34.7% for MSM2T group versus 8.5% for MSM1T (P < 0.001). Spina bifida diagnosis at 14-20 weeks declined from 38.8% in 2009 to 13.3% in 2011 (P < 0.001).

Conclusion: Loss of maternal serum alpha-fetoprotein had a tangible effect on the gestational age at diagnosis of spina bifida and resulted in a decrease of 25% of cases of spina bifida detected before 20 weeks. © 2017 John Wiley & Sons, Ltd.