La ecografía vaginal como factor pronóstico del parto prematuro

Resumen

Objetivo

Valorar la longitud del cuello del útero entre las semanas 20–24 de gestación, por ecografía vaginal, como factor pronóstico de parto prematuro en gestantes normales.

Sujetos y métodos

411 embarazos normales con feto único, sin selección, que acudían a consulta de obstetricia durante 2001–2002. Cuatro pacientes se perdieron y 5 partos fueron prematuros por indicación médica, quedando 402. Realizamos estudio longitudinal, prospectivo. Las pacientes se clasificaron utilizando un punto de corte de 30 mm.

Resultados

Hubo 17 (4,2%) partos prematuros espontáneos. Debajo de 30 mm había 21 gestantes con 5 partos prematuros; sensibilidad, 29,4%; valor predictivo positivo, 23,8%; especificidad, 95,8%; valor predictivo negativo, 96,9%, y razón de verosimilitud positiva, 7,1. En nulíparas aumenta la sensibilidad al 36,4%, el valor predictivo positivo al 30,8% y la razón de verosimilitud positiva al 8,9.

Conclusiones

La ecografía vaginal presenta baja sensibilidad, alta especificidad y no es útil como factor pronóstico del parto prematuro en embarazos normales.

Abstract

Objective

To evaluate the cervical length of the uterus between weeks 20 and 24 of gestation, using transvaginal ultrasound examination as a predictive factor of preterm labour in normal pregnancies.

Subjects and methods

We studied 411 unselected women with singleton pregnancies, who visited the obstetric service in 2001–2002. Four patients were lost to follow-up and there were 5 who had iatrogenic preterm delivery. A total of 402 women remained in the study We carried out a longitudinal, prospective study. The patients were classified according to a cut-off value of 30 mm.

Results

There were 17 spontaneous preterm labors (4.2%). Below the 30 mm cut-off point there were 21 pregnant women with 5 preterm labors; sensitivity: 29.4%, positive predictive value: 23.8%, specificity: 95.8%, negative predictive value: 96.9% and likelihood ratio 7.1. In primigravidae, sensitivity increased to 36.4%, positive predictive value to 30.8% and the likelihood ratio to 8.9.

Conclusions

Transvaginal ultrasound examination shows low sensitivity and high specificity. It is not useful as a predictive factor in normal pregnancies.