Background:

The standardized assessment of the hypoplastic nasal bone (NB) by ultrasonography between 11-14 weeks’ gestation has value in the detection of fetal aneuploidies. The frequency of hypoplastic NB varies between populations and is unknown in Mexico.

Objective:

To analyze the performance of hypoplastic NB for the early detection of fetal aneuploidies in a Mexican population.

Material and methods:

A nested case-control study in a cohort of Mexican pregnant women. The inclusion criteria were live fetus with crown-rump length (CRL) 45-84 mm and the result of perinatal karyotype or phenotype at birth. Ultrasonographic assessment of the NB was standardized. The statistical analyses were univariable, multiple logistic regression, Bayes’ theorem and performance.

Results:

A total of 65 cases and 1187 controls were studied, with maternal age of 17-53 years. The frequency of hypoplastic NB was 1.6% (95% CI = 0.9-2.3) in euploid fetuses versus 44.6% (95% CI = 32.5-56.7) with aneuploidies (p < 0.001, χ2). Sensitivity for trisomy 21 was 58.3% (PPV 52.5%, NPV 98.7%). The probability of the hypoplastic NB was conditioned by aneuploidy (type), CRL, and nuchal translucency. The C-statistic of the Bayesian model was 0.904 (95% CI = 0.842-0.965).

Conclusions:

A Mexican model of the NB had added value in the early detection of fetal aneuploidies.