S. Beck, D. Wojdyla, L. Say, A. Betran, M. Merialdi et al., The worldwide incidence of preterm birth: a systematic review of maternal mortality and morbidity, Bulletin of the World Health Organization, vol.88, issue.1, pp.31-38, 2009.
DOI : 10.2471/BLT.08.062554

J. Lawn, K. Kerber, and C. Enweronu-laryea, Cousens S: 3.6 million neonatal deaths--what is progressing and what is not? Semin Perinatol, pp.371-386, 2010.

J. Lawn, M. Gravett, T. Nunes, C. Rubens, and C. Stanton, Global report on preterm birth and stillbirth (1 of 7): definitions, description of the burden and opportunities to improve data, BMC Pregnancy and Childbirth, vol.10, issue.Suppl 1, pp.10-11, 2010.
DOI : 10.1016/S0020-7292(02)00234-5

L. Simmons, C. Rubens, G. Darmstadt, and M. Gravett, Preventing Preterm Birth and Neonatal Mortality: Exploring the Epidemiology, Causes, and Interventions, Seminars in Perinatology, vol.34, issue.6, pp.408-415, 2010.
DOI : 10.1053/j.semperi.2010.09.005

C. Howson, M. Kinney, and J. Lawn, Born too soon: the global action report on preterm birth, Geneva: World Health, 2012.

R. Goldenberg, J. Culhane, J. Iams, and R. Romero, Epidemiology and causes of preterm birth, The Lancet, vol.371, issue.9606, pp.75-84, 2008.
DOI : 10.1016/S0140-6736(08)60074-4

A. Schempf, A. Branum, S. Lukacs, and K. Schoendorf, Maternal age and parity-associated risks of preterm birth: differences by race/ethnicity, Paediatric and Perinatal Epidemiology, vol.87, issue.5, pp.34-43, 2007.
DOI : 10.1046/j.1365-3016.2002.00407.x

S. Glinianaia, J. Rankin, T. Pless-mulloli, M. Pearce, M. Charlton et al., Temporal changes in key maternal and fetal factors affecting birth outcomes: A 32-year population-based study in an industrial city, BMC Pregnancy and Childbirth, vol.112, issue.2, p.39, 2008.
DOI : 10.1111/j.1471-0528.2004.00311.x

K. Joseph, J. Fahey, N. Dendukuri, V. Allen, O. Campo et al., Recent Changes in Maternal Characteristics by Socioeconomic Status, Journal of Obstetrics and Gynaecology Canada, vol.31, issue.5, pp.422-433, 2009.
DOI : 10.1016/S1701-2163(16)34173-1

B. Blondel, K. Supernant, D. Mazaubrun, C. Breart, and G. , La sant?? p??rinatale en France m??tropolitaine de 1995 ?? 2003, Journal de Gyn??cologie Obst??trique et Biologie de la Reproduction, vol.35, issue.4, pp.373-387, 2006.
DOI : 10.1016/S0368-2315(06)76409-2

B. Blondel, N. Lelong, M. Kermarrec, and F. Goffinet, La sant?? p??rinatale en France m??tropolitaine de 1995???? 2010. R??sultats des enqu??tes nationales p??rinatales, Journal de Gyn??cologie Obst??trique et Biologie de la Reproduction, vol.41, issue.2, pp.151-166
DOI : 10.1016/j.jgyn.2011.11.008

P. Olsen, E. Laara, P. Rantakallio, M. Jarvelin, A. Sarpola et al., Epidemiology of Preterm Delivery in Two Birth Cohorts with an Interval of 20 Years, American Journal of Epidemiology, vol.142, issue.11, pp.1184-1193, 1995.
DOI : 10.1093/oxfordjournals.aje.a117577

B. Jacobsson, L. Ladfors, and I. Milsom, Advanced Maternal Age and Adverse Perinatal Outcome, Obstetrics & Gynecology, vol.104, issue.4, pp.727-733, 2004.
DOI : 10.1097/01.AOG.0000140682.63746.be

O. López and G. Bréart, Trends in gestational age and birth weight in Chile, 1991???2008. A descriptive epidemiological study, BMC Pregnancy and Childbirth, vol.69, issue.Suppl 2, p.121, 1991.
DOI : 10.1136/bmj.319.7222.1397

C. Albala and F. Vio, Epidemiological transition in Latin America: The case of Chile, Public Health, vol.109, issue.6, pp.431-442, 1995.
DOI : 10.1016/S0033-3506(95)80048-4

R. Platt, M. Abrahamowicz, M. Kramer, K. Joseph, L. Mery et al., Detecting and eliminating erroneous gestational ages: a normal mixture model, Statistics in Medicine, vol.59, issue.2, pp.3491-3503, 2001.
DOI : 10.1002/sim.1095

K. Joseph, M. Kramer, A. Allen, L. Mery, R. Platt et al., Implausible Birth Weight for Gestational Age, American Journal of Epidemiology, vol.153, issue.2, pp.110-113, 2001.
DOI : 10.1093/aje/153.2.110

C. Mcmahon, F. Gibson, J. Allen, and D. Saunders, Psychosocial adjustment during pregnancy for older couples conceiving through assisted reproductive technology, Human Reproduction, vol.22, issue.4, pp.1168-1174, 2007.
DOI : 10.1093/humrep/del502

B. Schonhaut, P. Rm, and D. Astudillo, Prematuros tard??os: un grupo de riesgo de morbilidad a corto y largo plazo, Revista chilena de pediatr??a, vol.83, issue.3, pp.217-223, 2012.
DOI : 10.4067/S0370-41062012000300002

J. Zhang and K. Yu, What's the Relative Risk?, JAMA, vol.280, issue.19, pp.1690-1691, 1998.
DOI : 10.1001/jama.280.19.1690

R. Platt, Logistic regression and odds ratios., Injury Prevention, vol.3, issue.4, p.294, 1997.
DOI : 10.1136/ip.3.4.294

N. Vargas, C. Villar, and A. Lastra, Change in reproductive partner among women delivering at a Metropolitan Santiago public hospital], Rev Med Chil, vol.132, pp.719-724, 2004.

L. Gibbons, J. Belizan, J. Lauer, A. Betran, M. Merialdi et al., Inequities in the use of cesarean section deliveries in the world, American Journal of Obstetrics and Gynecology, vol.206, issue.4, pp.331-331, 2012.
DOI : 10.1016/j.ajog.2012.02.026

F. Menacker, E. Declercq, and M. Macdorman, Cesarean Delivery: Background, Trends, and Epidemiology, Seminars in Perinatology, vol.30, issue.5, pp.235-241, 2006.
DOI : 10.1053/j.semperi.2006.07.002

URL : http://citeseerx.ist.psu.edu/viewdoc/summary?doi=

F. Barros, V. Mdel, and P. , Temporal Trends of Preterm Birth Subtypes and Neonatal Outcomes, Obstetrics & Gynecology, vol.107, issue.5, pp.1035-1041, 2006.
DOI : 10.1097/01.AOG.0000215984.36989.5e

J. Parker and K. Schoendorf, Implications of cleaning gestational age data, Paediatric and Perinatal Epidemiology, vol.110, issue.2, pp.181-187, 2002.
DOI : 10.1093/aje/153.2.110

T. Arbuckle, R. Wilkins, and G. Sherman, Birth weight percentiles by gestational age in Canada, Obstet Gynecol, vol.81, pp.39-48, 1993.

L. Foix-l-'helias and B. Blondel, Changes in risk factors of preterm delivery in France between 1981 and 1995, Paediatric and Perinatal Epidemiology, vol.29, issue.4, pp.314-323, 2000.
DOI : 10.1016/S0029-7844(97)00009-4

M. Keirse, M. Hanssens, and H. Devlieger, Trends in preterm births in Flanders, Belgium, from 1991 to 2002, Paediatric and Perinatal Epidemiology, vol.123, issue.1, pp.522-532, 1991.
DOI : 10.1111/j.1365-3016.2009.01067.x

J. Haas, R. Jackson, E. Fuentes-afflick, A. Stewart, M. Dean et al., Changes in the health status of women during and after pregnancy, Journal of General Internal Medicine, vol.51, issue.1, pp.45-51, 2005.
DOI : 10.1111/j.1525-1497.2004.40097.x

R. Molina, T. Molina, and E. González, Madres ni??as-adolescentes de 14 a??os y menos: Un grave problema de salud p??blica no resuelto en Chile, Revista m??dica de Chile, vol.135, issue.1, pp.79-86, 2007.
DOI : 10.4067/S0034-98872007000100011

K. Raatikainen, N. Heiskanen, P. Verkasalo, and S. Heinonen, Good outcome of teenage pregnancies in high-quality maternity care, The European Journal of Public Health, vol.16, issue.2, pp.157-161, 2006.
DOI : 10.1093/eurpub/cki158

K. Joseph, D. Young, L. Dodds, O. Connell, C. Allen et al., Changes in Maternal Characteristics and Obstetric Practice and Recent Increases in Primary Cesarean Delivery, Obstetrics & Gynecology, vol.102, issue.4, pp.791-800, 2003.
DOI : 10.1097/00006250-200310000-00022

E. Donoso, DESCENSO DE LA NATALIDAD EN CHILE: UN PROBLEMA PA??S, Revista chilena de obstetricia y ginecolog??a, vol.72, issue.2, pp.73-75, 2007.
DOI : 10.4067/S0717-75262007000200001

K. Raatikainen, N. Heiskanen, and S. Heinonen, Marriage still protects pregnancy, BJOG: An International Journal of Obstetrics & Gynaecology, vol.70, issue.1, pp.1411-1416, 2005.
DOI : 10.1111/j.1471-0528.2005.00667.x

P. Shah, J. Zao, and S. Ali, Maternal Marital Status and Birth Outcomes: A Systematic Review and Meta-Analyses, Maternal and Child Health Journal, vol.31, issue.4, pp.1097-1109, 2011.
DOI : 10.1007/s10995-010-0654-z