The significance of fetal maxillary length in the first trimester screening for trisomy 21.

OBJECTIVE

The present study aims to specify the significance of fetal maxillary length by establishing a nomogram for a Turkish population and by investigating its relationship with the ultrasonographic and biochemical parameters which are commonly used to screen trisomy 21 in the first trimester of pregnancy.

METHODS

The present observational study investigates 1,308 Turkish women who had 11- to 14-week-old singleton healthy pregnancies. Fetal crown-rump length (CRL), nuchal translucency (NT), nasal bone length (NBL) and maxillary length are measured by ultrasonography and maternal serum concentrations of pregnancy-associated plasma protein-A (PAPP-A) and free beta-human chorionic gonadotropin (HCG) are determined.

RESULTS

A positive and significant correlation was detected between the fetal maxillary length and gestational age (r = 0.309, P < 0.001) as was the case with fetal CRL (r = 0.357, P < 0.001) and NBL (r = 0.487, P < 0.001). Although there was a significant and positive correlation between fetal maxillary length and maternal serum PAPP-A levels (r = 0.201, P < 0.001), a significant and negative correlation was found between fetal maxillary length and the maternal serum concentrations of free beta-HCG (r = -0.238, P < 0.001). Fetal maxillary length increased in accordance with the advancing gestational age and increasing CRL. Maternal serum PAPP-A concentrations and fetal CRL and NBL were addressed as independent predictors of fetal maxillary length.

CONCLUSIONS

The length of fetal maxillary bone is a promising biometrical parameter which can be reliably and efficiently used to screen trisomy 21 in first trimester. Fetal maxillary length is also found to correlate with gestational age, CRL, NBL and PAPP-A significantly. It would be rational to use a combination of nasal and maxillary bone length measurements in case serum concentrations of PAPP-A or beta-HCG cannot be assessed.