BACKGROUND: The incidence of twin pregnancies is increasing in industrialized countries, including Norway. In the present nationwide study from Norway, we aimed at evaluating the effect of assisted reproductive technologies and delayed childbearing age on this epidemic rise. MATERIAL AND METHOD: Altogether 2.19 million pregnancies, including 27,849 twin pairs and higher-order multiples, were included in this population-based study with data from the Medical Birth Registry of Norway covering the years 1967-2004. The study period was divided into two, 1967-87 and 1988-2004, respectively. For the last time period, pregnancies from assisted reproductive technologies were available through a separate registration, and these data were linked with the Medical Birth Registry of Norway birth record. Additionally, we compared the twinning rates from natural conception in the two time periods in relation to maternal age. Logistic regression was used for adjusted odds ratio estimation. RESULTS: During 1967-1987, the twinning rate remained constant at 1.0% of the total number of births in Norway. Thereafter, the total twinning rate increased from 1.1% in 1988 to 1.9% in 2004. After excluding pregnancies from assisted reproductive technologies, the increase was from 1.1% to 1.6% in this period. There was a significantly higher twinning rate in all age groups in the time period 1988-2004 compared with 1967-1987. In naturally conceived pregnancies, OR for twins were 1.11 (95% CI 1.05-1.17) in the age group 20-24 years, 1.25 (95% CI 1.19-1.31) in the age group 30-34, and 1.36 (95% CI 1.11-1.67) in the age group 40-44 comparing the two time periods. CONCLUSIONS: The multiple pregnancy rate increased by 50% in Norway during the time period 1988-2004, even when twin pregnancies from assisted reproduction were excluded. Maternal age and assisted reproductive technologies cannot alone satisfactorily explain the rise in the twinning rate in Norway.
BACKGROUND: The incidence of twin pregnancies is increasing in industrialized countries, including Norway. In the present nationwide study from Norway, we aimed at evaluating the effect of assisted reproductive technologies and delayed childbearing age on this epidemic rise. MATERIAL AND METHOD: Altogether 2.19 million pregnancies, including 27,849 twin pairs and higher-order multiples, were included in this population-based study with data from the Medical Birth Registry of Norway covering the years 1967-2004. The study period was divided into two, 1967-87 and 1988-2004, respectively. For the last time period, pregnancies from assisted reproductive technologies were available through a separate registration, and these data were linked with the Medical Birth Registry of Norway birth record. Additionally, we compared the twinning rates from natural conception in the two time periods in relation to maternal age. Logistic regression was used for adjusted odds ratio estimation. RESULTS: During 1967-1987, the twinning rate remained constant at 1.0% of the total number of births in Norway. Thereafter, the total twinning rate increased from 1.1% in 1988 to 1.9% in 2004. After excluding pregnancies from assisted reproductive technologies, the increase was from 1.1% to 1.6% in this period. There was a significantly higher twinning rate in all age groups in the time period 1988-2004 compared with 1967-1987. In naturally conceived pregnancies, OR for twins were 1.11 (95% CI 1.05-1.17) in the age group 20-24 years, 1.25 (95% CI 1.19-1.31) in the age group 30-34, and 1.36 (95% CI 1.11-1.67) in the age group 40-44 comparing the two time periods. CONCLUSIONS: The multiple pregnancy rate increased by 50% in Norway during the time period 1988-2004, even when twin pregnancies from assisted reproduction were excluded. Maternal age and assisted reproductive technologies cannot alone satisfactorily explain the rise in the twinning rate in Norway.
Authors: M Delnord; K Szamotulska; A D Hindori-Mohangoo; B Blondel; A J Macfarlane; N Dattani; C Barona; S Berrut; I Zile; R Wood; L Sakkeus; M Gissler; J Zeitlin Journal: Eur J Public Health Date: 2016-01-10 Impact factor: 3.367
Authors: Anna Heino; Mika Gissler; Ashna D Hindori-Mohangoo; Béatrice Blondel; Kari Klungsøyr; Ivan Verdenik; Ewa Mierzejewska; Petr Velebil; Helga Sól Ólafsdóttir; Alison Macfarlane; Jennifer Zeitlin Journal: PLoS One Date: 2016-03-01 Impact factor: 3.240
Authors: Aline Jelenkovic; Yoshie Yokoyama; Reijo Sund; Chika Honda; Leonie H Bogl; Sari Aaltonen; Fuling Ji; Feng Ning; Zengchang Pang; Juan R Ordoñana; Juan F Sánchez-Romera; Lucia Colodro-Conde; S Alexandra Burt; Kelly L Klump; Sarah E Medland; Grant W Montgomery; Christian Kandler; Tom A McAdams; Thalia C Eley; Alice M Gregory; Kimberly J Saudino; Lise Dubois; Michel Boivin; Adam D Tarnoki; David L Tarnoki; Claire M A Haworth; Robert Plomin; Sevgi Y Öncel; Fazil Aliev; Maria A Stazi; Corrado Fagnani; Cristina D'Ippolito; Jeffrey M Craig; Richard Saffery; Sisira H Siribaddana; Matthew Hotopf; Athula Sumathipala; Fruhling Rijsdijk; Timothy Spector; Massimo Mangino; Genevieve Lachance; Margaret Gatz; David A Butler; Gombojav Bayasgalan; Danshiitsoodol Narandalai; Duarte L Freitas; José Antonio Maia; K Paige Harden; Elliot M Tucker-Drob; Bia Kim; Youngsook Chong; Changhee Hong; Hyun Jung Shin; Kaare Christensen; Axel Skytthe; Kirsten O Kyvik; Catherine A Derom; Robert F Vlietinck; Ruth J F Loos; Wendy Cozen; Amie E Hwang; Thomas M Mack; Mingguang He; Xiaohu Ding; Billy Chang; Judy L Silberg; Lindon J Eaves; Hermine H Maes; Tessa L Cutler; John L Hopper; Kelly Aujard; Patrik K E Magnusson; Nancy L Pedersen; Anna K Dahl Aslan; Yun-Mi Song; Sarah Yang; Kayoung Lee; Laura A Baker; Catherine Tuvblad; Morten Bjerregaard-Andersen; Henning Beck-Nielsen; Morten Sodemann; Kauko Heikkilä; Qihua Tan; Dongfeng Zhang; Gary E Swan; Ruth Krasnow; Kerry L Jang; Ariel Knafo-Noam; David Mankuta; Lior Abramson; Paul Lichtenstein; Robert F Krueger; Matt McGue; Shandell Pahlen; Per Tynelius; Glen E Duncan; Dedra Buchwald; Robin P Corley; Brooke M Huibregtse; Tracy L Nelson; Keith E Whitfield; Carol E Franz; William S Kremen; Michael J Lyons; Syuichi Ooki; Ingunn Brandt; Thomas Sevenius Nilsen; Fujio Inui; Mikio Watanabe; Meike Bartels; Toos C E M van Beijsterveldt; Jane Wardle; Clare H Llewellyn; Abigail Fisher; Esther Rebato; Nicholas G Martin; Yoshinori Iwatani; Kazuo Hayakawa; Joohon Sung; Jennifer R Harris; Gonneke Willemsen; Andreas Busjahn; Jack H Goldberg; Finn Rasmussen; Yoon-Mi Hur; Dorret I Boomsma; Thorkild I A Sørensen; Jaakko Kaprio; Karri Silventoinen Journal: Twin Res Hum Genet Date: 2015-09-04 Impact factor: 1.587