Studies that Calculate Risk of Stillbirth by Gestational Age

Studies since 1987 calculating risk of stillbirth by gestational age

Note: There are a couple of limitations when researchers try to figure out the risk of stillbirth by gestational age. First, the gestational age may not be accurate, especially if it comes from birth certificate data. Second, the stillbirth might not have occurred during that week—it could have occurred days or weeks earlier. Third, authors usually do not distinguish between antepartum stillbirths and intrapartum stillbirths. Antepartum stillbirths are usually due to severe maternal or fetal problems (although some are due to unknown causes), and intrapartum stillbirths are usually caused by fetal distress or problems with labor. Because these two types of stillbirths have different causes, it is important that they be looked at separately—but they usually are not (Kramer, Liu et al. 2002) (Kramer et al. 2002 for the third point only).

**This study was criticized in a letter to the editor written by Hilder, who disputed their use of the original data and said that the prospective risk was not the appropriate formula (Hilder, Costeloe et al. 2000). In an additional letter, Boulvain et al. (2000) said that “reporting fetal mortality as cumulative incidence is misleading if readers are not told the length of the period at risk. The clinician caring for a pregnant woman, and the woman herself, balance the risk of stillbirth with the probability of spontaneous onset of labour during a specific period (for example, until the next visit). The clinically relevant measure is either the rate or the risk of stillbirth during a limited period.”

References:

1. Ananth, C. V. et al. (2009). A comparison of foetal and infant mortality in the United States and Canada. Int J Epidemiol 38(2): 480-489.
2. Boulvain, M. et al. (2000). Prospective risk of stillbirth. Randomised trials of earlier induction of labour are needed. BMJ320(7232): 445; author reply 446.
3. Cotzias, C. S. et al. (1999). Prospective risk of unexplained stillbirth in singleton pregnancies at term: population based analysis. BMJ 319(7205): 287-288.
4. Divon, M. Y. et al. (2004). A functional definition of prolonged pregnancy based on daily fetal and neonatal mortality rates. Ultrasound Obstet Gynecol 23(5): 423-426.
5. Feldman, G. B. (1992). Prospective risk of stillbirth. Obstet Gynecol 79(4): 547-553.
6. Hilder, L. et al. (1998). Prolonged pregnancy: evaluating gestation-specific risks of fetal and infant mortality. Br J Obstet Gynaecol 105(2): 169-173.
7. Huang, D. Y. et al. (2000). Determinants of unexplained antepartum fetal deaths. Obstet Gynecol 95(2): 215-221.
8. Kramer, M. S. et al. (2002). Analysis of perinatal mortality and its components: time for a change? Am J Epidemiol 156(6): 493-497.
9. MacDorman, M. F. and S. Kirmeyer (2009). Fetal and perinatal mortality, United States, 2005. Natl Vital Stat Rep 57(8): 1-19.
10. Morken, N. H., K. Klungsoyr, et al. (2014). Perinatal mortality by gestational week and size at birth in singleton pregnancies at and beyond term: a nationwide population-based cohort study. BMC Pregnancy Childbirth 14: 172.
11. Olesen, A. W. et al. (2003). Perinatal and maternal complications related to postterm delivery: a national register-based study, 1978-1993. Am J Obstet Gynecol 189(1): 222-227.
12. Rosenstein, M. G. et al. (2012). Risk of stillbirth and infant death stratified by gestational age. Obstet Gynecol 120(1): 76-82.
13. Smith, G. C. (2001). Life-table analysis of the risk of perinatal death at term and post term in singleton pregnancies. Am J Obstet Gynecol 184(3): 489-496.
14. Weiss, E. et al. (2014). Fetal mortality at and beyond term in singleton pregnancies in Baden-Wuerttemberg/Germany 2004-2009.Arch Gynecol Obstet 289(1): 79-84.
15. Yudkin, P. L. et al. (1987). Risk of unexplained stillbirth at different gestational ages. Lancet 1(8543): 1192-1194.