Obstetric History and Risk of Short Cervix in Women with a Prior Preterm Birth

Abstract

Objective We aimed to assess the relationship between obstetric history and incidence of short cervical length (CL) at <24 weeks gestational age (GA) in women with a prior spontaneous preterm birth (PTB).

Study Design Women with a singleton gestation and a history of spontaneous PTB on progesterone who received prenatal care at a single center from 2011 to 2016 were included. Those who did not undergo screening or had a history-indicated cerclage were excluded. The associations between short CL (<25 mm) before 24 weeks and obstetrical factors including: number of prior PTBs, history of term birth, and GA of earliest spontaneous PTB were estimated through modified Poisson regression, adjusting for confounding factors. Multiple pregnancies for the same woman were accounted for through robust sandwich standard error estimation.

Results Among 773 pregnancies, 29% (n = 224) had a CL <25 mm before 24 weeks. The number of prior PTBs was not associated with short CL, but a prior full-term delivery conferred a lower risk of short CL (absolute risk reduction or aRR 0.79, 95% CI 0.63–1.00). Earliest GA of prior spontaneous PTB was associated with short CL. The strongest association was observed in women with a prior PTB at 16^0/7 to 23^6/7weeks (aRR 1.98, 95% CI: 1.46–2.70), compared with those with deliveries at 34^0/7 to 36^6/7 weeks. Yet, even women whose earliest PTB was 34^0/7 to 36^6/7 weeks remained at risk for a short CL, as 21% had a CL <25 mm. The number of prior PTBs did not modify the effect of GA of the earliest prior PTB (interaction test: p = 0.70).

Conclusion GA of earliest spontaneous PTB, but not the number of prior PTBs, is associated with short CL. Nevertheless, women with a history of later PTBs remain at sufficiently high risk of having a short CL at <24 weeks gestation that we cannot recommend modifications to existing CL screening guidelines in this group of women.

Key Points

• Prior 16 to 23^6/7 weeks birth is a key risk factor for CL <25 mm.

• One in five women with prior late PTB had a short CL.

• Number of PTBs is a less important risk factor.

Keywords

preterm birth - cervical length - short cervix - obstetric history

• References

• 1 Owen J, Hankins G, Iams JD. et al. Multicenter randomized trial of cerclage for preterm birth prevention in high-risk women with shortened mid trimester cervical length. Am J Obstet Gynecol 2009; 201 (04) 375.e1-375.e8
• 2 McIntosh J, Feltovich H, Berghella V, Manuck T. Society for Maternal-Fetal Medicine (SMFM). The role of routine cervical length screening in selected high- and low-risk women for preterm birth prevention. Am J Obstet Gynecol 2016; 215 (03) B2-B7
• 3 Einerson BD, Grobman WA, Miller ES. Cost-effectiveness of risk-based screening for cervical length to prevent preterm birth. Am J Obstet Gynecol 2016; 215 (01) 100.e1-100.e7
• 4 Werner EF, Hamel MS, Orzechowski K, Berghella V, Thung SF. Cost-effectiveness of transvaginal ultrasound cervical length screening in singletons without a prior preterm birth: an update. Am J Obstet Gynecol 2015; 213 (04) 554.e1-554.e6
• 5 Gonzalez-Quintero VH, Cordova YC, Istwan NB. et al. Influence of gestational age and reason for prior preterm birth on rates of recurrent preterm delivery. Am J Obstet Gynecol 2011; 205 (03) 275.e1-275.e5
• 6 Mercer BM, Goldenberg RL, Moawad AH. National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. et al. The preterm prediction study: effect of gestational age and cause of preterm birth on subsequent obstetric outcome. Am J Obstet Gynecol 1999; 181 (5 Pt 1): 1216-1221
• 7 McManemy J, Cooke E, Amon E, Leet T. Recurrence risk for preterm delivery. Am J Obstet Gynecol 2007; 196 (06) 576.e1-576.e6 , discussion 576.e6–576.e7
• 8 Iams JD, Grobman WA, Lozitska A. Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal–Fetal Medicine Units Network. et al. Adherence to criteria for transvaginal ultrasound imaging and measurement of cervical length. Am J Obstet Gynecol 2013; 209 (04) 365.e1-365.e5
• 9 Zou G. A modified Poisson regression approach to prospective studies with binary data. Am J Epidemiol 2004; 159 (07) 702-706
• 10 Iams JD, Johnson FF, Sonek J, Sachs L, Gebauer C, Samuels P. Cervical competence as a continuum: a study of ultrasonographic cervical length and obstetric performance. Am J Obstet Gynecol 1995;172(4 Pt 1):1097–1103, discussion 1104–1106
• 11 Wing DA, Szychowski J, Owen J. Vaginal Ultrasound Trial Consortium. et al. Gestational age at previous preterm birth does not affect cerclage efficacy. Am J Obstet Gynecol 2010; 203 (04) 377.e1-377.e4
• 12 Martin JA, Hamilton BE, Osterman MJK, Driscoll AK, Drake P. Births: final data for 2017. Natl Vital Stat Rep 2018; 67 (08) 1-50
• 13 Szychowski JM, Owen J, Hankins G. Vaginal Ultrasound Cerclage Trial Consortium. et al. Timing of mid-trimester cervical length shortening in high-risk women. Ultrasound Obstet Gynecol 2009; 33 (01) 70-75
• 14 Iams JD, Berghella V. Care for women with prior preterm birth. Am J Obstet Gynecol 2010; 203 (02) 89-100