Post-Term-Births

This report examines trends in post-term birth rates in KFL&A and Ontario.  Post-term births occur when the infant is born at 42 weeks gestation or later.  Post-term deliveries can cause complications for both the mother and infant.  Mothers who have had a post-term delivery have higher rates of developing complications such as postpartum hemorrhage, caesarean section, and peripheral nerve injury.¹

Post-term infants may have higher rates of perinatal and obstetric complications, including postpartum hemorrhage, caesarean delivery and perinatal mortality.^1;2  It was also found that infants born post-term with a low birth weight (<2500g) are at greater risk of developing complications, such as septicaemia, mortality within the first week of life, and asphyxia, before, during and after delivery.¹ Post-term infants born with a high birth weight (4500g) have a higher risk of developing pneumonia and meconium aspiration, which may be due to complicated vaginal deliveries.¹

Women who are older^3;4, primaparous^3;4, overweight or obese^3;4, have higher education,³ or who have had a previous post-term birth⁵ are more likely to have a post-term pregnancy.  There has been speculation that there may be a genetic component associated with post- term births.⁶

Figure 1.   Post-term birth rate (42+ weeks) for live, singleton births in KFL&A and Ontario, 2012-2013⁽⁷⁾

Interpretation of Figure 1.

Figure 1 displays the post-term birth rate per 100 live, singleton births in KFL&A and Ontario.⁷  The highest post-term birth rate is observed among mothers aged 45-49; however, this rate is based on a very small number of births and the rate may fluctuate from year to year.  It should be noted that, in Canada, mothers should be offered induction of labour at 41 or 42 weeks.⁸ 

Figure 2.   Post-term birth rate (42+ weeks) for live, singleton births by maternal age in KFL&A and Ontario, 2012-2013⁽⁹⁾

Interpretation of Figure 2.

For a complete list of data sources and terms used in the Reproductive Health Facts & Figures, see the Facts & Figures titled "Data Sources for Reproductive Health" and "Glossary for Reproductive Health" located on the Facts & Figures webpage in the Reproductive Health section.

1. 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;189:222-227.
2. Smith GC. Life-table analysis of the risk of perinatal death at term and post term in singleton pregnancies. Am J Obstet Gynecol 2001;184:489-496.
3. 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;177:531-537.
4. Roos N, Sahlin L, Ekman-Ordeberg G, Kieler H, Stephansson O. Maternal risk factors for postterm pregnancy and cesarean delivery following labor induction. Acta Obstet Gynecol Scand 2010;89:1003-1010.
5. Mogren I, Stenlund H, Hogberg U. Recurrence of prolonged pregnancy. Int J Epidemiol 1999;28:253-257.
6. Laursen M, Bille C, Olesen AW, Hjelmborg J, Skytthe A, Christensen K. Genetic influence on prolonged gestation: a population-based Danish twin study. Am J Obstet Gynecol 2004;190:489-494.
7. Inpatient Discharges: Calendar years 2005-2013. Ontario Ministry of Health and Long-Term Care, IntelliHEALTH ONTARIO. [extracted 2014 Nov 25]
8. Delaney M, Roggensack A. Guidelines for the Management of Pregnancy at 41+0 to 42+0 weeks. J Obstet Gynnaecol Can 2008;214:800-810.
9. BORN Information System (Fiscal years: 2012-2013) Date Extracted: Nov. 24, 2014.