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Biparietal/transverse abdominal diameter ratio ≤ 1: potential marker for open spina bifida at 11-13-week scan
E G Simon1, C J Arthuis, G Haddad
1University Hospital Center of Tours, Department of Obstetrics, Gynecology and Fetal Medicine, Tours, France; Inserm U930, François Rabelais University, Tours, France.
Insights
Screening for open spina bifida in early pregnancy can be improved by using the biparietal diameter to transverse abdominal diameter (BPD/TAD) ratio. This simple ultrasound marker enhances detection rates compared to BPD alone.
Area of Science:
- Prenatal diagnostics
- Fetal medicine
- Obstetrics
Background:
- Open spina bifida is a serious birth defect.
- First-trimester biparietal diameter (BPD) below the 5th percentile detects about half of open spina bifida cases.
- A novel screening method using the BPD/transverse abdominal diameter (TAD) ratio was investigated.
Purpose of the Study:
- To evaluate the effectiveness of the BPD/TAD ratio in first-trimester screening for open spina bifida.
- To compare the BPD/TAD ratio's performance against BPD alone.
Main Methods:
- Retrospective analysis of 20,551 first-trimester ultrasound scans (11-13 weeks' gestation).
- Included 26 cases of open spina bifida and 17,665 unaffected pregnancies.
- Measurements analyzed included biparietal diameter (BPD) and transverse abdominal diameter (TAD).
Main Results:
- The mean BPD/TAD ratio was significantly different between fetuses with and without spina bifida (1.00 vs. 1.13, P < 0.0001).
- BPD/TAD ratio ≤ 1.00 detected 69.2% of open spina bifida cases, outperforming BPD ≤ 5th percentile (46.2%).
- Combining both markers identified 76.9% of cases with a 5.1% false-positive rate.
Conclusions:
- The BPD/TAD ratio significantly improves the detection of open spina bifida in early pregnancy.
- This screening method is simple, effective, and suitable for widespread application in prenatal care.
Objective:
In the first trimester of pregnancy, a biparietal diameter (BPD) below the 5(th) percentile is a simple marker that enables the prenatal detection of half of all cases of open spina bifida. We hypothesized that relating the BPD measurement to the transverse abdominal diameter (TAD) might be another simple and effective screening method. In this study we assessed the performance of using the BPD/TAD ratio during the first trimester of pregnancy in screening for open spina bifida.
Methods:
A total of 20,551 first-trimester ultrasound scans (11-13 weeks' gestation), performed between 2000 and 2013, were analyzed retrospectively; there were 26 cases of open spina bifida and 17,665 unaffected pregnancies with a crown-rump length of 45-84 mm and a record of both BPD and TAD measurements.
Results:
The mean (± SD) BPD/TAD ratio was 1.00 ± 0.06 for fetuses with spina bifida and 1.13 ± 0.06 for those without (P < 0.0001). A BPD ≤ 5(th) percentile enabled the prenatal detection of 46.2% of spina bifida cases, while a BPD/TAD ratio of ≤ 1.00 detected 69.2%. If we considered cases in which either BPD was ≤ 5(th) percentile or BPD/TAD ratio was ≤ 1, we identified 76.9% of cases. In the latter case, the false-positive rate was 5.1%, while that for using a combination of both BPD ≤ 5th percentile and BPD/TAD ratio ≤ 1 was 0.6%, with a sensitivity of 38.5%. The positive predictive value of using a combination of BPD ≤ 5th percentile and BPD/TAD ratio ≤ 1 for detecting spina bifida was 8.5%.
Conclusions:
Between 11 and 13 weeks' gestation, relating BPD to TAD improves considerably the diagnostic performance of using BPD measurement alone in screening for open spina bifida. Screening using this marker is simple and applicable to a large population.
