Obstet Gynecol Sci.  2023 Jan;66(1):1-10. 10.5468/ogs.22263.

Prenatal screening for neural tube defects: from maternal serum alpha-fetoprotein to ultrasonography

• Kim GJ
• Seong JS
• Oh JA

• KMID: 2538343
• DOI: http://doi.org/10.5468/ogs.22263

Abstract

The two main screening tests during pregnancy are those for chromosomal abnormalities and neural tube defects (NTDs). In particular, for NTDs, measurement of maternal serum alpha-fetoprotein (MSAFP) levels early in the second trimester (15-18 weeks of gestation) has been considered the gold standard screening test for the past 4 decades. However, with remarkable technological advancements and the widespread use of ultrasound during those periods, mid-trimester ultrasonography has gradually replaced the role of measuring MSAFP levels as a screening method for NTDs. This change was initiated more about 10 years ago in some countries, which have issued national guidelines to use mid-trimester ultrasonography instead of measuring MSAFP levels as a prenatal screening method for NTDs. However, no significant changes have occurred in Korea, where second-trimester ultrasonography is routinely performed with high-quality equipment. We aimed to provide information regarding the importance of changing the screening method for NTDs from MSAFP measurement to ultrasonography, and to detail methods of implementing mid-trimester ultrasonography for screening purposes. We also share our experience of operating a prenatal diagnostic program for NTDs without using MSAFP for more than 15 years.

Keyword

Neural tube defects; Alpha-fetoprotein; Ultrasonography

Figure

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  Fig. 1 Indirect brain signs of the fetus affected by open spinal neural tube defects. (A) Abnormal skull shape (lemon sign, arrows) and ventriculomegaly at 18 gestational weeks; (B) abnormal cerebellum (banana sign, arrow) at 19 gestational weeks.

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  Fig. 2 Axial planes of a normal fetal spine at 25 gestational weeks. (A) Axial plane view of the cervical spine; (B) axial plane view of the thoracic spine; (C) axial plane view of the lumbar spine; (D) axial plane view of the sacrum (arrows: pedicles, arrowhead: vertebral body).

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  Fig. 3 Sagittal plane view of the normal spine and conus medullaris (CM) at 22 gestational weeks (arrow: filum terminale, arrowhead: central canal).

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  Fig. 4 Coronal plane views of the lumbosacral spine at 25 gestational weeks. (A) Single line (arrowhead: vertebral body) of ossification; (B) double line (arrows: pedicles) of ossification; (C) triple line of ossification (arrows: pedicles, arrowhead: vertebral body). (D) Three-dimensional image of the fetal spine at 21 gestational weeks.

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  Fig. 5 Ultrasound images of spinal neural tube defects. (A) Protruding cystic mass (arrow) in sagittal plane; (B) indented skin line (arrow) in the sagittal plane; (C) indented skin (arrow) in the coronal plane; (D) ruptured meningomyelocele (arrow) with contour of the lesion (arowheads) in the coronal plane.

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