Objective
Achondroplasia is the most common nonlethal skeletal dysplasia and, despite its autosomal dominant inheritance, most cases are sporadic, resulting from a de novo paternal mutation in the fibroblast growth factor receptor-3 gene. We recently demonstrated that the femoral diaphyseal-metaphyseal angle (DMA) can be measured accurately by ultrasound. We reported that in the third trimester the angle was on average 36% wider in those with achondroplasia than in normal fetuses, measuring >130 degrees in 83% of cases. When compared with other antenatal ultrasound features, other than shortening of the long bones, such as macrocephaly and frontal bossing, a widened femoral DMA was the most consistent finding. However, little is known about the DMA in the second trimester in fetuses with achondroplasia. The main challenge in the prenatal diagnosis of this condition is that the fetal biometry and anatomy are usually normal at the second-trimester anomaly scan, and the traditional ultrasound features are usually apparent only from approximately 25 weeks’ gestation, which means that the diagnosis is usually late in pregnancy or indeed postnatal. Here we report the identification of a wide femoral DMA at the 20- to 23-week anomaly scan in fetuses with achondroplasia, weeks before the other ultrasound features of this condition become apparent.
Study design
Cases with achondroplasia (n = 4) confirmed in the third trimester or after birth and a group of normal fetuses (n = 164) were included in this case-control study. At 20 +0 to 23 +6 weeks’ gestation the femoral angle between the diaphysis and the metaphysis was prospectively measured at a 45-degree insonation angle in the normal group. For the achondroplasia group images of femur length measurements taken at 20 +0 to 23 +6 weeks were retrieved and the femoral angle was retrospectively measured. Regression analysis was used to identify potential confounders that might affect the femoral DMA.
Study design
Cases with achondroplasia (n = 4) confirmed in the third trimester or after birth and a group of normal fetuses (n = 164) were included in this case-control study. At 20 +0 to 23 +6 weeks’ gestation the femoral angle between the diaphysis and the metaphysis was prospectively measured at a 45-degree insonation angle in the normal group. For the achondroplasia group images of femur length measurements taken at 20 +0 to 23 +6 weeks were retrieved and the femoral angle was retrospectively measured. Regression analysis was used to identify potential confounders that might affect the femoral DMA.
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