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Snell, BJ. Assessment and management of bleeding in the first trimester of pregnancy.. Journal of Midwifery & Women's Health. Nov–Dec 2009, 54 (6): 483–91. PMID 19879521. doi:10.1016/j.jmwh.2009.08.007.
Dole, N.; Savitz, D. A.; Hertz-Picciotto, I.; Siega-Riz, A. M.; McMahon, M. J.; Buekens, P. Maternal stress and preterm birth. American Journal of Epidemiology. 2003-01-01, 157 (1): 14–24. ISSN 0002-9262. PMID 12505886. doi:10.1093/aje/kwf176.
Tunon, K.; Eik-Nes, S. H.; Grøttum, P.; Von Düring, V.; Kahn, J. A. Gestational age in pregnancies conceived after in vitro fertilization: A comparison between age assessed from oocyte retrieval, crown-rump length and biparietal diameter. Ultrasound in Obstetrics and Gynecology. 2000, 15 (1): 41–46. PMID 10776011. doi:10.1046/j.1469-0705.2000.00004.x.
Snell, BJ. Assessment and management of bleeding in the first trimester of pregnancy.. Journal of Midwifery & Women's Health. Nov–Dec 2009, 54 (6): 483–91. PMID 19879521. doi:10.1016/j.jmwh.2009.08.007.
Dole, N.; Savitz, D. A.; Hertz-Picciotto, I.; Siega-Riz, A. M.; McMahon, M. J.; Buekens, P. Maternal stress and preterm birth. American Journal of Epidemiology. 2003-01-01, 157 (1): 14–24. ISSN 0002-9262. PMID 12505886. doi:10.1093/aje/kwf176.
Dole, N.; Savitz, D. A.; Hertz-Picciotto, I.; Siega-Riz, A. M.; McMahon, M. J.; Buekens, P. Maternal stress and preterm birth. American Journal of Epidemiology. 2003-01-01, 157 (1): 14–24. ISSN 0002-9262. PMID 12505886. doi:10.1093/aje/kwf176.