Citation Information :
Belics Z, Papp Z. Ultrasonographic Assessment of the Cervix for Prediction of Spontaneous Preterm Birth in Singleton Pregnancies. Donald School J Ultrasound Obstet Gynecol 2021; 15 (1):49-63.
Spontaneous preterm birth remains a major cause of neonatal morbidity and mortality across the world. Hence, there is an urgent need to find and implement diagnostic methods and interventions that can reduce this public health treat. The ultrasonographic assessment of the cervix is one tool that can be utilized to identify women at increased risk who may be candidates for preventive interventions. There are three main characteristics of the cervix, which can be evaluated during the ultrasound examination of the cervix: cervical length (CL), funneling and cervical gland area. Cervical shortening is one of the first steps in the processes leading to labor and can precede labor by several weeks. Because shortening begins at the internal cervical os and progresses caudally, it is often detected on ultrasound examination before it can be appreciated on physical examination. This is equally true for funneling and cervical gland area (CGA), which cannot be assessed with the physical examination. Based on previous experiences, the timing and frequency of ultrasonographic assessment of the cervix is primarily based on the patient\'s prior obstetric history (low-risk women are screened once at 18–24 weeks of gestation; high-risk population usually begins screening at about 16 weeks of gestation and the frequency depends on the measurement result). Classically the diagnosis of short cervix is defined when the CL is less than or equal to 25 mm at these gestational weeks, with the best prediction for PTB obtained at 16–24 weeks of gestation. The CL measurement, evaluation of funneling and CGA together increased the sensitivity of cervical screening for PTB and appeared to be powerful predictor of PTB before 32 weeks gestation. Generally, the importance of positive test is to try to recognize cervical changes on time, to plane the adequate therapy, to prepare for sufficient intrauterine transport, and to administered course of antenatal corticosteroid therapy to women at risk for PTB reduced the incidence and severity of respiratory distress syndrome (RDS) and mortality in offspring. Many interventions (bed rest, lifestyle intervention, cervical cerclage, pessary, progesteron, indomethacin, antibiotics, etc.) have been proposed in an attempt to prevent PTB depending on risk classification.
WHO. WHO: recommended definitions, terminology and format for statistical tables related to the perinatal period and use of a new certificate for cause of perinatal deaths. Modifications recommended by FIGO as amended october 14, 1976. Acta Obstet Gynecol Scand 1977;56(3):247–253.
Rogers LK, Velten M. Maternal inflammation, growth retardation, and preterm birth: insights into adult cardiovascular disease. Life Sci 2011;89(13-14):417–421. DOI: 10.1016/j.lfs.2011.07.017.
Blencowe H, Lee AC, Cousens S, et al. Preterm birth associated neurodevelopmental impairment estimates at regional and global level for 2010. Pediatr Res 2013;74(Suppl 1):17–34. DOI: 10.1038/pr.2013.204.
Rodrigues T, Rocha L, Barros H. Physical abuse during pregnancy and preterm delivery. Am J Obstet Gynecol 2008;198(2):171–176. DOI: 10.1016/j.ajog.2007.05.015.
Caughey AB, (2007). Definition, incidence, significance and demographic characteristics of preterm birth. [online] UpToDate. Available from: http://www.uptodate.com/contents/demographic-factors-inpreterm-birth [Accessed June 2018].
Lockwood CJ, (2007) Overview of preterm labor and delivery. [online] UpToDate. Available from: http://www.uptodate.com/contents/fetal-fibronectin-forprediction-of-preterm-labor-and-delivery [Accessed June 2018].
Robinson JN, Norwitz E, (2007). Risk factors for preterm labor and delivery. [online] UpToDate. Available from: https://www.uptodate.com/contents/preterm-birth-risk-factors-and-interventions-for-risk-reduction [Accessed Jun 2018].
Crane JM, Delaney T, Hutchens D. Transvaginal ultrasonography in the prediction of preterm birth after treatment for cervical intraepithelial neoplasia. Obstet Gynecol 2006;107(1):37–44. DOI: 10.1097/01.AOG.0000192169.44775.76.
Arbyn M, Kyrgiou M, Simoens C, et al. Perinatal mortality and other severe adverse pregnancy outcomes associated with treatment of cervical intraepithelial neoplasia: meta-analysis. BMJ 2008;337(sep18 1):a1284. DOI: 10.1136/bmj.a1284.
Jolley JA, Wing DA. Pregnancy management after cervical surgery. Curr Opin Obstet Gynecol 2008;20(6):528–533. DOI: 10.1097/GCO.0b013e328317a411.
Dasanayake AP, Gennaro S, Hendricks-Muñoz KD, et al. Maternal periodontal disease, pregnancy, and neonatal outcomes. MCN Am J Matern Child Nurs 2008;33(1):45–49. DOI: 10.1097/01.NMC.0000305657.24613.47.
Yudin MH, Money DM, SOGC Infectious Diseases Committee Screening and management of bacterial vaginosis in pregnancy. SOGC clinical Practice guideline no. 211, August 2008. J Obstet Gynaecol Can 2008;30(8):702–716. DOI: 10.1016/S1701-2163(16)32919-X.
Viswanathan M, Siega-Riz AM, Moos MK, et al. Outcomes of maternal weight gain. Evid Rep Technol Assess (Full Rep) 2008;168:1–223.
Iams JD, Goldenberg RL, Meis PJ, et al. The length of the cervix and the risk of spontaneous premature delivery. National Institute of Child Health and Human Development Maternal Fetal Medicine Unit Network. N Engl J Med 1996;334(9):567–572. DOI: 10.1056/NEJM199602293340904.
Owen J, Yost N, Berghella V, et al. Can shortened midtrimester cervical length predict very early spontaneous preterm birth? Am J Obstet Gynecol 2004;191(1):298–303. DOI: 10.1016/j.ajog.2003.11.025.
Blondel B, Le Coutour X, Kaminski M, et al. Prediction of preterm delivery: is it substantially improved by routine vaginal examinations? Am J Obstet Gynecol 1990;162(4):1042–1048. DOI: 10.1016/0002-9378(90)91312-Z.
Berghella V, Bega G, Tolosa JE, et al. Ultrasound assessment of the cervix. Clin Obstet Gynecol 2003;46(4):947–962. DOI: 10.1097/00003081-200312000-00026.
Hassan SS, Romero R, Berry SM, et al. Patients with an ultrasonographic cervical length < or =15 mM have nearly a 50% risk of early spontaneous preterm delivery. Am J Obstet Gynecol 2000;182(6):1458–1467. DOI: 10.1067/mob.2000.106851.
Hernandez-Andrade E, Romero R, Ahn H, et al. Transabdominal evaluation of uterine cervical length during pregnancy fails to identify a substantial number of women with a short cervix. J Matern Fetal Neonatal Med 2012;25(9):1682–1689. DOI: 10.3109/14767058.2012.657278.
Saul LL, Kurtzman JT, Hagemann C, et al. Is transabdominal sonography of the cervix after voiding a reliable method of cervical length assessment? J Ultrasound Med 2008;27(9):1305–1311. DOI: 10.7863/jum.2008.27.9.1305.
Hassan SS, Romero R, Vidyadhari D, et al. Vaginal progesterone reduces the rate of preterm birth in women with a sonographic short cervix: a multicenter, randomized, double-blind, placebo-controlled trial. Ultrasound Obstet Gynecol 2011;38(1):18–31. DOI: 10.1002/uog.9017.
Goya M, Pratcorona L, Merced C, et al. Cervical pessary in pregnant women with a short cervix (PECEP): an open-label randomised controlled trial. Lancet 2012;379(9828):1800–1806. DOI: 10.1016/S0140-6736(12)60030-0.
Althuisius SM, Dekker GA, Hummel P, et al. Cervical incompetence prevention randomized cerclage trial: emergency cerclage with bed rest versus bed rest alone. Am J Obstet Gynecol 2003;189(4):907–910. DOI: 10.1067/S0002-9378(03)00718-X.
Kagan KO, Sonek J. How to measure cervical length. Obstet Gynecol 2015;45(3):358–362. DOI: 10.1002/uog.14742.
Berghella V, Owen J, MacPherson C, et al. Natural history of cervical funneling in women at high risk for spontaneous preterm birth. Obstet Gynecol 2007;109(4):863–869. DOI: 10.1097/01.AOG.0000258276.64005.ce.
Owen J, Yost N, Berghella V, et al. Mid-trimester endovaginal sonography in women at high risk for spontaneous preterm birth. JAMA 2001;286(11):1340–1348. DOI: 10.1001/jama.286.11.1340.
Yost NP, Bloom SL, Twickler DM, et al. Pitfalls in ultrasonic cervical length measurement for predicting preterm birth. Obstet Gynecol 1999;93(4):510–516. DOI: 10.1097/00006250-199904000-00008.
Iams JD, Johnson FF, Sonck J, et al. 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. DOI: 10.1016/0002-9378(95)91469-2.
Hibbard JU, Tart M, Moawad AH. Cervical length at 16-22 weeks’ gestation and risk for preterm delivery. Obstet Gynecol 2000;96(6):972–978. DOI: 10.1097/00006250-200012000-00020.
Cahill AG, Odibo AO, Caughey AB, et al. Universal cervical length screening and treatment with vaginal progesterone to prevent preterm birth: a decision and economic analysis. Am J Obstet Gynecol 2010;202(6):548.e1-8. DOI: 10.1016/j.ajog.2009.12.005.
Werner EF, Han CS, Pettker CM, et al. Universal cervical-length screening to prevent preterm birth: a cost-effectiveness analysis. Ultrasound Obstet Gynecol 2011;38(1):32–37. DOI: 10.1002/uog.8911.
Heath VCF, Southall TR, Souka AP, et al. Cervical length at 23 weeks of gestation: relation to demographic characteristics and previous obstetric history. Ultrasound Obstet Gynecol 1998;12(5):304–311. DOI: 10.1046/j.1469-0705.1998.12050304.x.
Greco E, Gupta R, Syngelaki A, et al. First-trimester screening for spontaneous preterm delivery with maternal characteristics and cervical length. Fetal Diagn Ther 2012;31(3):154–161. DOI: 10.1159/000335686.
To MS, Skentou C, Cicero S, et al. Cervical assessment at the routine 23-weeks’ scan: problems with transabdominal sonography. Ultrasound Obstet Gynecol 2000;15(4):292–296. DOI: 10.1046/j.1469-0705.2000.00094.x.
Taipale P, Hiilesmaa V. Sonographic measurement of uterine cervix at 18-22 weeks’ gestation and the risk of preterm delivery. Obstet Gynecol 1998;92(6):902–907. DOI: 10.1016/S0029-7844(98)00346-9.
Kushnir O, Vigil DA, Izquierdo L, et al. Vaginal ultrasonographic assessment of cervical length changes during normal pregnancy. Am J Obstet Gynecol 1990;162(4):991–993. DOI: 10.1016/0002-9378(90)91302-S.
Andersen HF, Nugent CE, Wanty SD, et al. Prediction of risk for preterm delivery by ultrasonographic measurement of cervical length. Am J Obstet Gynecol 1990;163(3):859–867. DOI: 10.1016/0002-9378(90)91084-P.
Zorzoli A, Soliani A, Perra M, et al. Cervical changes throughout pregnancy as assessed by transvaginal sonography. Obstet Gynecol 1994;84(6):960–964.
Zilianti M, Azuaga A, Calderon F, et al. Monitoring the effacement of the uterine cervix by transperineal sonography: a new perspective. J Ultrasound Med 1995;14(10):719–724. DOI: 10.7863/jum.19184.108.40.2069.
Gramellini D, Fieni S, Molina E, et al. Transvaginal sonographic cervical length changes during normal pregnancy. J Ultrasound Med 2002;21(3):227–232. DOI: 10.7863/jum.2002.21.3.227.
Bega G, Lev-Toaff A, Kuhlman K, et al. Three-dimensional multiplanar transvaginal ultrasound of the cervix in pregnancy. Ultrasound Obstet Gynecol 2000;16(4):351–358. DOI: 10.1046/j.1469-0705.2000.00184.x.
Towner D, Boe N, Lou K, et al. Cervical length measurements in pregnancy are longer when measured with three-dimensional transvaginal ultrasound. J Maternal Fetal Neonat Med 2004;16(3):167–170. DOI: 10.1080/jmf.220.127.116.11.
Severi FM, Bocchi C, Florio P, et al. Comparison of two-dimensional and three-dimensional ultrasound in the assessment of the cervix to predict preterm delivery. Ultrasound Med Biol 2003;29(9):1261–1265. DOI: 10.1016/S0301-5629(03)01011-1.
Moroz LA, Simhan HN. Rate of sonographic cervical shortening and the risk of spontaneous preterm birth. Am J Obstet Gynecol 2012;206(3):234.e1-5. DOI: 10.1016/j.ajog.2011.11.017.
Iams JD, Cebrik D, Lynch C, et al. The rate of cervical change and the phenotype of spontaneous preterm birth. Am J Obstet Gynecol 2011;205(2):130. DOI: 10.1016/j.ajog.2011.05.021.
Berghella V, Roman A, Daskalakis C, et al. Gestational age at cervical length measurement and incidence of preterm birth. Obstet Gynecol 2007;110(2 Pt 1):311–317. DOI: 10.1097/01.AOG.0000270112.05025.1d.
Crane JM, Hutchens D. Transvaginal sonographic measurement of cervical length to predict preterm birth in asymptomatic women at increased risk: a systematic review. Ultrasound Obstet Gynecol 2008;31(5):579–587. DOI: 10.1002/uog.5323.
Conde-Agudelo A, Romero R. Predictive accuracy of changes in transvaginal sonographic cervical length over time for preterm birth: a systematic review and metaanalysis. Am J Obstet Gynecol 2015;213(6):789–801. DOI: 10.1016/j.ajog.2015.06.015.
Owen J, Hankins G, Iams JD, et al. Multicenter randomized trial of cerclage for preterm birth prevention in high-risk women with shortened midtrimester cervical length. Am J Obstet Gynecol 2009;201(4):375.e1-8. DOI: 10.1016/j.ajog.2009.08.015.
Berghella V, Talucci M, Desai A. Does transvaginal sonographic measurement of cervical length before 14 weeks predict preterm delivery in high-risk pregnancies? Ultrasound Obstet Gynecol 2003;21(2):140–144. DOI: 10.1002/uog.28.
Conoscenti G, Meir YJ, D’Ottavio G, et al. Does cervical length at 13-15 weeks’ gestation predict preterm delivery in an unselected population? Ultrasound Obstet Gynecol 2003;21(2):128–134. DOI: 10.1002/uog.47.
Ludmir J. Sonographic detection of cervical incompetence. Clin Obstet Gynecol 1988;31(1):101–109. DOI: 10.1097/00003081-198803000-00012.
Iams JD, Goldenberg RL, Mercer BM, et al. The preterm prediction study: can low-risk women destined for spontaneous preterm birth be identified? Am J Obstet Gynecol 2001;184(4):652–655. DOI: 10.1067/mob.2001.111248.
Mella MT, Berghella V. Prediction of preterm birth: cervical sonography. Semin Perinatol 2009;33(5):317–324. DOI: 10.1053/j.semperi.2009.06.007.
Miller ES, Tita AT, Grobman WA. Second-trimester cervical length screening among asymptomatic women: an evaluation of risk-based strategies. Obstet Gynecol 2015;126(1):61–66. DOI: 10.1097/AOG.0000000000000864.
Kushnir O, Izquierdo LA, Smith JF, et al. Transvaginal sonographic measurement of cervical length. Evaluation of twin pregnancies. J Reprod Med 1995;40(5):380–382.
Wennerholm UB, Holm B, Mattsby-Baltzer I, et al. Fetal fibronectin, endotoxin, bacterial vaginosis and cervical length as predictors of preterm birth and neonatal morbidity in twin pregnancies. Br J Obstet Gynaecol 1997;104(12):1398–1404. DOI: 10.1111/j.1471-0528.1997.tb11010.x.
Guzman ER, Walters C, O’reilly-Green C, et al. Use of cervical ultrasonography in prediction of spontaneous preterm birth in triplet gestations. Am J Obstet Gynecol 2000;183(5):1108–1113. DOI: 10.1067/mob.2000.108875.
Goldenberg RL, Iams JD, Miodovnik M, et al. The preterm prediction study: risk factors in twin gestations. National institute of child health and human development maternal-fetal medicine units network. Am J Obstet Gynecol 1996;175(4 Pt 1):1047–1053. DOI: 10.1016/S0002-9378(96)80051-2.
Committee on Practice Bulletins—Obstetrics. The american college of obstetricians and gynecologists. Practice bulletin no. 130: prediction and prevention of preterm birth. Obstet Gynecol 2012;120(4):964–973. DOI: 10.1097/AOG.0b013e3182723b1b.
Committee on Practice Bulletins—Obstetrics and the American Institute of Ultrasound in Medicine. Practice bulletin no. 175: ultrasound in pregnancy. Obstet Gynecol 2016;128(6):e241–e256. DOI: 10.1097/AOG.0000000000001815.
McIntosh J, Feltovich H, Berghella V, et al. Society for Maternal-Fetal Medicine (SMFM), electronic address: Pubs@SMFM.org, the role of routine cervical length screening in selected high- and low-risk women for preterm birth prevention. Am J Obstet Gynecol 2016;215(3):B2–B7. DOI: 10.1016/j.ajog.2016.04.027.
Podobnik M, Bulié M, Smiljanicé N, et al. Ultrasonography in the detection of cervical incompetency. J Clin Ultrasound 1988;13(6):383–391. DOI: 10.1002/jcu.1870160604.
Michaels WH, Montgomery C, Karo J, et al. Ultrasound differentiation of the competent from the incompetent cervix: prevention of preterm delivery. Am J Obstet Gynecol 1986;154(3):537–546. DOI: 10.1016/0002-9378(86)90598-3.
Varma TR, Patel RH, Pillai U. Ultrasound assessment of the cervix in ‘at risk’ patients. Acta Obstet Gynecol Scand 1986;65(2):147–152. DOI: 10.3109/00016348609158370.
Bartolucci L, Hill WC, Katz M, et al. Ultrasonography in preterm labor. Am J Obstet Gynecol 1984;149(1):52–56. DOI: 10.1016/0002-9378(84)90291-6.
Sekiya T, Ishihara K, Yoshimatsu K, et al. Detection rate of the cervical gland area during pregnancy by transvaginal sonography in the assessment of cervical maturation. Ultrasound Obstet Gynecol 1998;12(5):328–333. DOI: 10.1046/j.1469-0705.1998.12050328.x.
Savitha C, Arpitha JV, Nagarathnamma R. Significance of cervical length and cervical gland area in cervical maturation. Int J Reprod Contracept Obstet Gynecol 2016;5(8):2634–2639.
Yoshimatsu K, Sekiya T, Ishihara K, et al. Detection of the cervical gland area in threatened preterm labour using transvaginal sonography in the assessment of cervical maturation and pregnancy outcome. Gynecol Obstet Invest 2005;53(3):149–159. DOI: 10.1159/000058366.
Asakura H, Fukami T, Kurashina R, et al. Significance of cervical gland area in predicting preterm delivery birth for patients with the threatened preterm delivery. Comparison CL and the fetal fibronectin. Gynecol Obstet Invest 2009;68(1):1–8. DOI: 10.1159/000209394.
Pires CR, Moron AF, Mattar R, et al. Cervical gland area as an ultrasonographic marker for preterm delivery. Int J Gynecol Obstet 2006;93(3):214–219. DOI: 10.1016/j.ijgo.2005.12.010.
Espinoza J, Gonçalves LF, Romero R, et al. The prevalence and clinical significance of amniotic fluid ‘sludge’ in patients with preterm labor and intact membranes. Ultrasound Obstet Gynecol 2005;25(4):346–352. DOI: 10.1002/uog.1871.
Kusanovic JP, Espinoza J, Romero R, et al. Clinical significance of the presence of amniotic fluid ‘sludge’ in asymptomatic high-risk patients for spontaneous preterm delivery. Ultrasound Obstet Gynecol 2007;30(5):706–714. DOI: 10.1002/uog.4081.
Goldenberg RL, Cliver SP, Bronstein J, et al. Bed rest in pregnancy. Obstet Gynecol 1994;84(1):131–136.
Sciscione AC. Maternal activity restriction and the prevention of preterm birth. Am J Obstet Gynecol 2010;202(3):232.e1-5. DOI: 10.1016/j.ajog.2009.07.005.
Sosa CG, Althabe F, Belizán JM, et al. Bed rest in singleton pregnancies for preventing preterm birth. Cochrane Database Syst Rev 2015(3):CD003581. DOI: 10.1002/14651858.CD003581.pub3.
Grobman WA, Gilbert SA, Iams JD, et al. Activity restriction among women with a short cervix. Obstet Gynecol 2013;121(6):1181–1186. DOI: 10.1097/AOG.0b013e3182917529.
Abdul Sultan A, West J, Tata LJ, et al. Risk of first venous thromboembolism in pregnant women in hospital: population based cohort study from England. BMJ 2013;347(nov07 15):6099. DOI: 10.1136/bmj.f6099.
Yost NP, Owen J, Berghella V, et al. Effect of coitus on recurrent preterm birth. Obstet Gynecol 2006;107(4):793–797. DOI: 10.1097/01.AOG.0000206757.92602.b5.
Hibbard JU, Snow J, Moawad AH. Short cervical length by ultrasound and cerclage. J Perinatol 2000;20(3):161–165. DOI: 10.1038/sj.jp.7200333.
Dijkstra K, Funai EF, O’Neill L, et al. Change in cervical length after cerclage as a predictor of preterm delivery. Obstet Gynecol 2000;96(2):346–350. DOI: 10.1097/00006250-200009000-00006.
Rust OA, Atlas RO, Reed J, et al. Revisiting the short cervix detected by transvaginal ultrasound in the second trimester: why cerclage therapy may not help. Am J Obstet Gynecol 2001;185(5):1098–1105. DOI: 10.1067/mob.2001.118163.
To MS, Alfirevic Z, Heath VCF, et al. Cervical cerclage for prevention of preterm delivery in women with short cervix: randomised controlled trial. Lancet 2004;363(9424):1849–1853. DOI: 10.1016/S0140-6736(04)16351-4.
Berghella V, Keeler SM, To MS, et al. Effectiveness of cerclage according to severity of cervical length shortening: a meta-analysis. Ultrasound Obstet Gynecol 2010;35(4):468–473. DOI: 10.1002/uog.7547.
Nott JP, Bonney EA, Pickering JD, et al. The structure and function of the cervix during pregnancy. Translation Res Anatomy 2016;2:1–7. DOI: 10.1016/j.tria.2016.02.001.
Dodd JM, Flenady V, Cincotta R, et al. Prenatal administration of progesterone for preventing preterm birth. Cochrane Database Syst Rev 2006(1):CD004947.
Romero R, Nicolaides KH, Conde‐Agudelo A, et al. Vaginal progesterone decreases preterm birth ≤ 34 weeks of gestation in women with a singleton pregnancy and a short cervix: an updated meta-analysis including data from the OPPTIMUM study. Ultrasound Obstet Gynecol 2016;48(3):308–317. DOI: 10.1002/uog.15953.
Fonseca EB, Celik E, Parra M, et al. Progesterone and the risk of preterm birth among women with a short cervix. N Eng J Med 2007;357(5):462–469. DOI: 10.1056/NEJMoa067815.
Norwitz ER, (2017). Progesterone supplementation to reduce the risk of spontaneous preterm birth. [online] UpToDate. Available from: https://www.uptodate.com/contents/progesterone-supplementation-to-reduce-the-risk-of-spontaneous-preterm-birth [Accessed June 2018].
Meis PJ, Klebanoff M, Thom E, et al. Prevention of recurrent preterm delivery by 17 alpha-hydroxyprogesterone caproate. N Engl J Med 2003;348(24):2379–2385. DOI: 10.1056/NEJMoa035140.
Romero R, Yeo L, Chaemsaithong P, et al. Progesterone to prevent spontaneous preterm birth. Semin Fetal Neonatal Med 2014;19(1):15–26. DOI: 10.1016/j.siny.2013.10.004.
da Fonseca EB, Bittar RE, Carvalho MHB, et al. Prophylactic administration of progesterone by vaginal suppository to reduce the incidence of spontaneous preterm birth in women at increased risk: a randomized placebo-controlled double-blind study. Am J Obstet Gynecol 2003;188(2):419–424. DOI: 10.1067/mob.2003.41.
Northen AT, Norman GS, Anderson K, et al. Follow-up of children exposed in utero to 17 alpha-hydroxyprogesterone caproate compared with placebo. Obstet Gynecol 2007;110(4):865–872. DOI: 10.1097/01.AOG.0000281348.51499.bc.
Briery CM, Veillon EW, Klauser CK, et al. Women with preterm premature rupture of the membranes do not benefit from weekly progesterone. Am J Obstet Gynecol 2011;204(1):54.e1-5. DOI: 10.1016/j.ajog.2010.08.022.
Combs CA, Garite T, Maurel K, et al. 17-hydroxyprogesterone caproate for twin pregnancy: a double-blind, randomized clinical trial. Am J Obstet Gynecol 2011;204(3):221.e1-8. DOI: 10.1016/j.ajog.2010.12.042.
Caritis SN, Rouse DJ, Peaceman AM, et al. Prevention of preterm birth in triplets using 17 alpha-hydroxyprogesterone caproate: a randomized controlled trial. Obstet Gynecol 2009;113(2 Pt 1):285–292. DOI: 10.1097/AOG.0b013e318193c677.
US Food and Drug Administration, Center for Drug Evaluation and Research. (2006). Summary minutes of the Advisory Committee for Reproductive Health Drugs, August 29, 2006. [online]. Available from: http://www.fda.gov/ohrms/dockets/ac/06/minutes/2006-4227M1.pdf [accessed June 2018].
Silver RI, Rodriguez R, Chang TSK, et al. In vitro fertilization is associated with an increased risk of hypospadias. J Urol 1999;161(6):1954–1957. DOI: 10.1016/S0022-5347(05)68863-5.
Carmichael SL, Shaw GM, Laurent C, et al. Maternal progestin intake and risk of hypospadias. Arch Pediatr Adolesc Med 2005;159(10):957–962. DOI: 10.1001/archpedi.159.10.957.
Attardi BJ, Zeleznik A, Simhan H, et al. Comparison of progesterone and glucocorticoid receptor binding and stimulation of gene expression by progesterone, 17-alpha hydroxyprogesterone caproate, and related progestins. Am J Obstet Gynecol 2007;197(6):599.e1-7. DOI: 10.1016/j.ajog.2007.05.024.
Background Document for Meeting of Advisory Committee for Reproductive Health Drugs. January 20, 2012. NDA 22-139. (2012). Progesterone gel (8%). [online] FDA. Available from: http://www.fda.gov/downloads/AdvisoryCommittees/CommitteesMeetingMaterials/Drugs/ReproductiveHealthDrugsAdvisoryCommittee/UCM287987.pdf [accessed June 2018].
Berghella V, Rust OA, Althuisius SM. Short cervix on ultrasound: does indomethacin prevent preterm birth? Am J Obstet Gynecol 2006;195(3):809–813. DOI: 10.1016/j.ajog.2006.06.007.
King J, Flenady V. Prophylactic antibiotics for inhibiting preterm labour with intact membranes. Cochrane Database Syst Rev 2002(4):CD000246.
Bujold E, Pasquier JC, Simoneau J, et al. Intra-amniotic sludge, short cervix, and risk of preterm delivery. J Obstet Gynaecol Can 2006;28(3):198–202. DOI: 10.1016/S1701-2163(16)32108-9.
Orzechowski KM, Boelig R, Nicholas SS, et al. Is universal cervical length screening indicated in women with prior term birth? Am J Obstet Gynecol 2015;212(2):234.e1. DOI: 10.1016/j.ajog.2014.08.029.
Berghella V, (2018). Second-trimester evaluation of cervical length for prediction of spontaneous preterm birth in singleton gestations. [online] UpToDate. Available from: https://www.uptodate.com/contents/second-trimester-evaluation-of-cervical-length-for-prediction-of-spontaneous-preterm-birth-in-singleton-gestations [Accessed Jun 2018].
Berghella V, Odibo AO, To MS, et al. Cerclage for short cervix on ultrasonography: meta-analysis of trials using individual patient-level data. Obstet Gynecol 2005;106(1):181–189. DOI: 10.1097/01.AOG.0000168435.17200.53.
Conde-Agudelo A, Romero R, Nicolaides K, et al. Vaginal progesterone vs. cervical cerclage for the prevention of preterm birth in women with a sonographic short cervix, previous preterm birth, and singleton gestation: a systematic review and indirect comparison metaanalysis. Am J Obstet Gynecol 2013;208(1):42.e1–42.e18. DOI: 10.1016/j.ajog.2012.10.877.