Association between cervical length and gestational age at birth in singleton pregnancies: a multicentric prospective cohort study in the Brazilian population
Authors: Silva Thais Valéria , Borovac-Pinheiro Anderson , Cecatti José Guilherme , Mol Ben Willem , Silva Costa Fabricio , França Marcelo Santucci , Souza Renato Teixeira , Devlieger Roland , Passini Renato , Carvalho Pacagnella Rodolfo ,   The P5 working group, Hatanaka Allan R , Dantas Amanda , Moron Antonio Fernandes , Menezes Carlos Augusto Santos , Paiva Cláudio Sérgio Medeiros , Marques Cristhiane B , Pereira Cynara Maria , dos Santos Lopes Homenko Daniela , Paiva Djacyr Magna Cabral , Moisés Elaine Christine Dantas , Barreto Enoch Quinderé Sá , Soares Felipe , Peixoto-Filho Fernando Maia , de Lucena Feitosa Francisco Edson , Carvalho Francisco Herlanio Costa , Boechem Jessica Scremin , Benini-Junior João Renato , Lima José Airton Oliveira , Argenton Juliana P. , Marquart Kaline F , Fernandes Karayna Gil , Andrade Kleber Cursino , Katz Leila , Machado Maíra Rossmann , Nomura Marcelo L , Lima Marcelo Marques Souza , Nakamura-Pereira Marcos , Miele Maria Julia , Costa Maria Laura , Dias Mário Correia , Ellovitch Nathalia , Sass Nelson , Camargo Rodrigo Pauperio Soares , de Oliveira Silva Savazoni Sabrina , Haddad Samira El Maerrawi Tebecherane , Martins-Costa Sérgio , Bento Silvana F , Quintana Silvana Maria , Sarmento Stéphanno Gomes Pereira , Fanton Tatiana F , Guedes Thaísa Bortoletto , de Andrade Junior Valter Lacerda 
Published: March 2023

Abstract
Background
Short cervical length measured during the second trimester of pregnancy is an important risk factor for spontaneous preterm birth (sPTB). The aim of this study is to identify the association between mid-pregnancy cervical length (CL) and gestational age at birth in asymptomatic singleton pregnant women.

Methods
This is a prospective cohort study involving singleton pregnant women who participated in the screening phase of a Brazilian multicenter randomized controlled trial (P5 trial) between July 2015 and March 2019. Transvaginal ultrasound to measure CL was performed from 18 to 22 + 6 weeks. Women with CL ≤ 30 mm received vaginal progesterone (200 mg/day) until 36 weeks’ gestation. For this analysis we considered all women with CL ≤ 30 mm receiving progesterone and a random selection of women with CL > 30 mm, keeping the populational distribution of CL. We obtained prognostic effectiveness data (area under receive operating characteristic curve (AUC), sensitivity and specificity and estimated Kaplan–Meier curves for preterm birth using different CL cutoff points.

Results
We report on 3139 women and identified a negative association between cervical length and sPTB. CL ≤ 25 mm was associated with sPTB < 28, sPTB < 34 and sPTB < 37 weeks, whereas a CL 25–30 mm was directly associated with late sPTB. CL by transvaginal ultrasound presented an AUC of 0.82 to predict sPTB < 28 weeks and 0.67 for sPTB < 34 weeks. Almost half of the sPTB occurred in nulliparous women and CL ≤ 30 mm was associated with sPTB at < 37 weeks (OR = 7.84; 95%CI = 5.5–11.1). The number needed to screen to detect one sPTB < 34 weeks in women with CL ≤ 25 mm is 121 and we estimated that 248 screening tests are necessary to prevent one sPTB < 34 weeks using progesterone prophylaxis.

Conclusions
CL measured by transvaginal ultrasound should be used to predict sPTB < 34 weeks. Women with CL ≤ 30 mm are at increased risk for late sPTB.