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Postterm pregnancy

Errol R Norwitz, MD, PhD
Section Editor
Charles J Lockwood, MD, MHCM
Deputy Editor
Vanessa A Barss, MD, FACOG


The timely onset of labor and delivery is an important determinant of perinatal outcome. Both preterm and postterm births are associated with higher rates of perinatal morbidity and mortality than pregnancies delivering at term.


Postterm pregnancy refers to a pregnancy that is ≥420/7ths weeks of gestation or ≥294 days from the first day of the last menstrual period [1]. Accurate pregnancy dating is critical to the diagnosis.

By comparison, preterm is < 370/7 weeks, early term is 370/7 weeks through 386/7 weeks, full term is 390/7 weeks through 406/7 weeks, and late term is 410/7 weeks through 416/7 weeks [2,3].


In the United States, approximately 28 percent of pregnancies deliver in the 40th and 41st week and 5.6 percent deliver at ≥42 weeks [4]. A study of postterm birth rates in 13 European countries observed a wide range across the continent: from 0.4 percent in Austria and Belgium to 8.1 percent in Denmark [5]. The authors attributed the variation to differences in prenatal assessment of gestational age and obstetric practices.

The prevalence of postterm pregnancy in a population is affected by several factors. One of the most important factors is whether routine early ultrasound assessment of gestational age is performed. Among pregnancies dated by first trimester ultrasound examination, the prevalence of delivery ≥42 weeks is about 2 percent (versus 6 to 12 percent by last menstrual period [LMP]) [6-9] and the prevalence of delivery ≥41 weeks ranges from 5 to 11 percent (versus 13 to 22 percent by LMP) [8,10-12]. In a meta-analysis that compared the rate of labor induction for postterm pregnancy in women who underwent sonographic estimation of their delivery date (EDD) in early pregnancy with the rate in women whose EDD was calculated from their LMP, early routine ultrasound examination reduced the rate of intervention for postterm pregnancy (OR 0.68, 95% CI 0.57-0.82) [6].


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Literature review current through: Sep 2015. | This topic last updated: Sep 14, 2015.
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  1. World Health Organization. International Statistical Classification of Diseases and Related Health Problems. Geneva, 2006.
  2. Spong CY. Defining "term" pregnancy: recommendations from the Defining "Term" Pregnancy Workgroup. JAMA 2013; 309:2445.
  3. ACOG Committee Opinion No 579: Definition of term pregnancy. Obstet Gynecol 2013; 122:1139.
  4. Martin JA, Hamilton BE, Ventura SJ, et al. Births: final data for 2011. Natl Vital Stat Rep 2013; 62:1.
  5. Zeitlin J, Blondel B, Alexander S, et al. Variation in rates of postterm birth in Europe: reality or artefact? BJOG 2007; 114:1097.
  6. Neilson JP. Ultrasound for fetal assessment in early pregnancy. Cochrane Database Syst Rev 2000; :CD000182.
  7. Caughey AB, Nicholson JM, Washington AE. First- vs second-trimester ultrasound: the effect on pregnancy dating and perinatal outcomes. Am J Obstet Gynecol 2008; 198:703.e1.
  8. Blondel B, Morin I, Platt RW, et al. Algorithms for combining menstrual and ultrasound estimates of gestational age: consequences for rates of preterm and postterm birth. BJOG 2002; 109:718.
  9. Bukowski R, Saade G, Malone F, et al. A decrease in postdates pregnancies is an additional benefit of first trimester screening for aneuploidy. Am J Obstet Gynecol 2001; 185:S148.
  10. Clinical Practice Obstetrics Committee, Maternal Fetal Medicine Committee, Delaney M, et al. Guidelines for the management of pregnancy at 41+0 to 42+0 weeks. J Obstet Gynaecol Can 2008; 30:800.
  11. Kramer MS, McLean FH, Boyd ME, Usher RH. The validity of gestational age estimation by menstrual dating in term, preterm, and postterm gestations. JAMA 1988; 260:3306.
  12. Bennett KA, Crane JM, O'shea P, et al. First trimester ultrasound screening is effective in reducing postterm labor induction rates: a randomized controlled trial. Am J Obstet Gynecol 2004; 190:1077.
  13. Oberg AS, Frisell T, Svensson AC, Iliadou AN. Maternal and fetal genetic contributions to postterm birth: familial clustering in a population-based sample of 475,429 Swedish births. Am J Epidemiol 2013; 177:531.
  14. Taylor NF. Review: placental sulphatase deficiency. J Inherit Metab Dis 1982; 5:164.
  15. Mogren I, Stenlund H, Högberg U. Recurrence of prolonged pregnancy. Int J Epidemiol 1999; 28:253.
  16. Olesen AW, Basso O, Olsen J. Risk of recurrence of prolonged pregnancy. BMJ 2003; 326:476.
  17. Kistka ZA, Palomar L, Boslaugh SE, et al. Risk for postterm delivery after previous postterm delivery. Am J Obstet Gynecol 2007; 196:241.e1.
  18. Kortekaas JC, Kazemier BM, Ravelli AC, et al. Recurrence rate and outcome of postterm pregnancy, a national cohort study. Eur J Obstet Gynecol Reprod Biol 2015; 193:70.
  19. Laursen M, Bille C, Olesen AW, et al. Genetic influence on prolonged gestation: a population-based Danish twin study. Am J Obstet Gynecol 2004; 190:489.
  20. Morken NH, Melve KK, Skjaerven R. Recurrence of prolonged and post-term gestational age across generations: maternal and paternal contribution. BJOG 2011; 118:1630.
  21. Divon MY, Ferber A, Nisell H, Westgren M. Male gender predisposes to prolongation of pregnancy. Am J Obstet Gynecol 2002; 187:1081.
  22. Stotland NE, Washington AE, Caughey AB. Prepregnancy body mass index and the length of gestation at term. Am J Obstet Gynecol 2007; 197:378.e1.
  23. Caughey AB, Stotland NE, Washington AE, Escobar GJ. Who is at risk for prolonged and postterm pregnancy? Am J Obstet Gynecol 2009; 200:683.e1.
  24. Denison FC, Price J, Graham C, et al. Maternal obesity, length of gestation, risk of postdates pregnancy and spontaneous onset of labour at term. BJOG 2008; 115:720.
  25. Knox GE, Huddleston JF, Flowers CE Jr. Management of prolonged pregnancy: results of a prospective randomized trial. Am J Obstet Gynecol 1979; 134:376.
  26. Yeh SY, Read JA. Management of post-term pregnancy in a large obstetric population. Obstet Gynecol 1982; 60:282.
  27. Lagrew DC, Freeman RK. Management of postdate pregnancy. Am J Obstet Gynecol 1986; 154:8.
  28. Feldman GB. Prospective risk of stillbirth. Obstet Gynecol 1992; 79:547.
  29. Olesen AW, Westergaard JG, Olsen J. Perinatal and maternal complications related to postterm delivery: a national register-based study, 1978-1993. Am J Obstet Gynecol 2003; 189:222.
  30. Spellacy WN, Miller S, Winegar A, Peterson PQ. Macrosomia--maternal characteristics and infant complications. Obstet Gynecol 1985; 66:158.
  31. Rosen MG, Dickinson JC. Management of post-term pregnancy. N Engl J Med 1992; 326:1628.
  32. Lu Y, Zhang J, Lu X, et al. Secular trends of macrosomia in southeast China, 1994-2005. BMC Public Health 2011; 11:818.
  33. Vorherr H. Placental insufficiency in relation to postterm pregnancy and fetal postmaturity. Evaluation of fetoplacental function; management of the postterm gravida. Am J Obstet Gynecol 1975; 123:67.
  34. Shime J, Librach CL, Gare DJ, Cook CJ. The influence of prolonged pregnancy on infant development at one and two years of age: a prospective controlled study. Am J Obstet Gynecol 1986; 154:341.
  35. Mannino F. Neonatal complications of postterm gestation. J Reprod Med 1988; 33:271.
  36. Bruckner TA, Cheng YW, Caughey AB. Increased neonatal mortality among normal-weight births beyond 41 weeks of gestation in California. Am J Obstet Gynecol 2008; 199:421.e1.
  37. Heuser C, Manuck T, Hossain S, et al. Non-anomalous stillbirth by gestational age: trends differ based on method of epidemiologic calculation. J Matern Fetal Neonatal Med 2010; 23:720.
  38. Cotzias CS, Paterson-Brown S, Fisk NM. Prospective risk of unexplained stillbirth in singleton pregnancies at term: population based analysis. BMJ 1999; 319:287.
  39. Rasmussen S, Albrechtsen S, Irgens LM, et al. Risk factors for unexplained antepartum fetal death in Norway 1967-1998. Early Hum Dev 2003; 71:39.
  40. Hannah ME. Postterm pregnancy: should all women have labour induced? A review of the literature. Fetal and Maternal Medicine Review 1993; 5:3.
  41. Divon MY, Haglund B, Nisell H, et al. Fetal and neonatal mortality in the postterm pregnancy: the impact of gestational age and fetal growth restriction. Am J Obstet Gynecol 1998; 178:726.
  42. Bakketeig LS, Bergsjo P. Post-term pregnancy: magnitude of the problem. In: Effective Care in Pregnancy and Childbirth, Enkin M, Keirse MJ, Chalmers I (Eds), Oxford University Press, Oxford 1989.
  43. Nakling J, Backe B. Pregnancy risk increases from 41 weeks of gestation. Acta Obstet Gynecol Scand 2006; 85:663.
  44. De Los Santos-Garate AM, Villa-Guillen M, Villanueva-García D, et al. Perinatal morbidity and mortality in late-term and post-term pregnancy. NEOSANO perinatal network's experience in Mexico. J Perinatol 2011; 31:789.
  45. Treger M, Hallak M, Silberstein T, et al. Postterm pregnancy: Should the definition of 42 weeks be reconsidered? [Abstract no. 452] Society for Maternal-Fetal Medicine, Miami, FL, 2000.
  46. Alexander JM, McIntire DD, Leveno KJ. Forty weeks and beyond: pregnancy outcomes by week of gestation. Obstet Gynecol 2000; 96:291.
  47. Alexander JM, MCIntire DD, Leveno KJ. Prolonged pregnancy: induction of labor and cesarean births. Obstet Gynecol 2001; 97:911.
  48. A clinical trial of induction of labor versus expectant management in postterm pregnancy. The National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Units. Am J Obstet Gynecol 1994; 170:716.
  49. Gülmezoglu AM, Crowther CA, Middleton P, Heatley E. Induction of labour for improving birth outcomes for women at or beyond term. Cochrane Database Syst Rev 2012; 6:CD004945.
  50. Divon MY, Ferber A, Sanderson M, et al. A functional definition of prolonged pregnancy based on daily fetal and neonatal mortality rates. Ultrasound Obstet Gynecol 2004; 23:423.
  51. Caughey AB, Sundaram V, Kaimal AJ, et al. Systematic review: elective induction of labor versus expectant management of pregnancy. Ann Intern Med 2009; 151:252.
  52. Heimstad R, Romundstad PR, Hyett J, et al. Women's experiences and attitudes towards expectant management and induction of labor for post-term pregnancy. Acta Obstet Gynecol Scand 2007; 86:950.
  53. National Collaborating Centre for Women’s and Children’s Health Clinical Guideline. Induction of Labour. July 2008. http://www.guideline.gov/content.aspx?id=14308 (Accessed on September 18, 2015).
  54. Menticoglou SM, Hall PF. Routine induction of labour at 41 weeks gestation: nonsensus consensus. BJOG 2002; 109:485.
  55. Heimstad R, Romundstad PR, Salvesen KA. Induction of labour for post-term pregnancy and risk estimates for intrauterine and perinatal death. Acta Obstet Gynecol Scand 2008; 87:247.
  56. American College of Obstetricians and Gynecologists. Practice bulletin no. 146: Management of late-term and postterm pregnancies. Obstet Gynecol 2014; 124:390.
  57. de Miranda E, van der Bom JG, Bonsel GJ, et al. Membrane sweeping and prevention of post-term pregnancy in low-risk pregnancies: a randomised controlled trial. BJOG 2006; 113:402.
  58. Myers ER, Blumrick R, Christian AL, et al. Management of Prolonged Pregnancy. Rockville (MD): Agency for Healthcare Research and Quality (US); 2002 May. (Evidence Reports/Technology Assessments, No. 53.)
  59. Alfirevic Z, Walkinshaw SA. A randomised controlled trial of simple compared with complex antenatal fetal monitoring after 42 weeks of gestation. Br J Obstet Gynaecol 1995; 102:638.
  60. Stokes HJ, Roberts RV, Newnham JP. Doppler flow velocity waveform analysis in postdate pregnancies. Aust N Z J Obstet Gynaecol 1991; 31:27.
  61. Practice bulletin no. 145: antepartum fetal surveillance. Obstet Gynecol 2014; 124:182.
  62. Guidetti DA, Divon MY, Langer O. Postdate fetal surveillance: is 41 weeks too early? Am J Obstet Gynecol 1989; 161:91.
  63. Bochner CJ, Williams J 3rd, Castro L, et al. The efficacy of starting postterm antenatal testing at 41 weeks as compared with 42 weeks of gestational age. Am J Obstet Gynecol 1988; 159:550.
  64. Phelan JP, Platt LD, Yeh SY, et al. The role of ultrasound assessment of amniotic fluid volume in the management of the postdate pregnancy. Am J Obstet Gynecol 1985; 151:304.
  65. Crowley P, O'Herlihy C, Boylan P. The value of ultrasound measurement of amniotic fluid volume in the management of prolonged pregnancies. Br J Obstet Gynaecol 1984; 91:444.
  66. Oz AU, Holub B, Mendilcioglu I, et al. Renal artery Doppler investigation of the etiology of oligohydramnios in postterm pregnancy. Obstet Gynecol 2002; 100:715.
  67. Tongsong T, Srisomboon J. Amniotic fluid volume as a predictor of fetal distress in postterm pregnancy. Int J Gynaecol Obstet 1993; 40:213.
  68. Bochner CJ, Medearis AL, Davis J, et al. Antepartum predictors of fetal distress in postterm pregnancy. Am J Obstet Gynecol 1987; 157:353.
  69. Morris JM, Thompson K, Smithey J, et al. The usefulness of ultrasound assessment of amniotic fluid in predicting adverse outcome in prolonged pregnancy: a prospective blinded observational study. BJOG 2003; 110:989.
  70. Clement D, Schifrin BS, Kates RB. Acute oligohydramnios in postdate pregnancy. Am J Obstet Gynecol 1987; 157:884.