Assessment of Length of Maternal Cervix between 18 and 24 weeks of Gestation in a Low-Risk Brazilian Population

Abstract

Purpose To determine cervical biometry in pregnant women between 18 and 24 weeks of gestation and the ideal mode of measurement of cervical length in cases of curved and straight cervical morphology.

Methods The uterine cervices of 752 low-risk pregnant women were assessed using transvaginal ultrasound in a prospective cross-sectional study. In women with straight uterine cervices, cervical biometry was performed in a continuous manner. In women with curved uterine cervices, the biometry was performed using both the continuous and segmented techniques (in segments joining the cervical os). Polynomial regression models were created to assess the correlation between the cervical length and gestational age. The paired Student t-test was used to compare measuring techniques.

Results The cervical biometry results did not vary significantly with the gestational age and were best represented by linear regression (R² = 0.0075 with the continuous technique, and R² = 0.0017 with the segmented technique). Up to the 21^st week of gestation, there was a predominance of curved uterine cervix morphology (58.9%), whereas the straight morphology predominated after this gestational age (54.2%). There was a significant difference between the continuous and the segmented measuring methods in all the assessed gestational ages (p < 0.001).

Conclusion Cervical biometry in pregnant women between 18 and 24 weeks was represented by a linear regression, independently of the measuring mode. The ideal measuring technique was the transvaginal ultrasound performed at a gestational age ≥21 weeks.

Resumo

Objetivo Determinar a biometria cervical em gestantes entre a 18ª e 24ª semanas, e ainda a forma ideal de mensuração do comprimento do colo uterino em casos de morfologias curva e reta.

Métodos Foram realizadas avaliações ultrassonográficas via vaginal dos colos uterinos de 752 gestantes de baixo risco em um estudo prospectivo transversal. Nos colos uterinos retos a biometria cervical foi feita de forma contínua, enquanto nos colos uterinos curvos, a biometria foi realizada de duas formas, contínua e fracionada (em segmentos unindo os orifícios do colo). Para avaliar a correlação entre o comprimento do colo uterino e a idade gestacional, foram criados modelos de regressão polinomial. Para se comparar a técnicas de medida do colo uterino, utilizou-se o teste t-Student pareado.

Resultados A biometria do colo uterino não variou de forma significativa com a idade gestacional, sendo melhor representada por uma regressão linear (R² = 0,0075 na forma contínua, e R² = 0,0017 na forma fracionada, respectivamente). Observamos que até a 21ª semana houve predominância de colos curvos (58,9%), porém após esta idade gestacional a morfologia retilínea predominou (54,2%). Houve diferença estatisticamente significativa entre a forma de mensuração contínua e fracionada em todas as idades gestacionais avaliadas (p < 0,001).

Conclusão A expressão da biometria cervical em gestantes entre 18 e 24 semanas é praticamente uma reta, independente da forma de mensuração. A forma ideal de medida é por ultrassonografia transvaginal realizada em idade gestacional ≥21 semanas.

Keywords

gestation - uterine cervix - biometry - morphology - transvaginal ultrasound

Descritores

Gestação - Colo uterino - Biometria - Morfologia - Ultrassom transvaginal

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