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This is an update of the Norwegian Mother and Child Cohort Study (MoBa) cohort profile which was published in 2006. Pregnant women attending a routine ultrasound examination were initially invited. The first child was born in October 1999 and the last in July 2009. The participation rate was 41%. The cohort includes more than 114 000 children, 95 000 mothers and 75 000 fathers. About 1900 pairs of twins have been born. There are approximately 16 400 women who participate with more than one pregnancy. Blood samples were obtained from both parents during pregnancy and from mothers and children (umbilical cord) after birth. Samples of DNA, RNA, whole blood, plasma and urine are stored in a biobank. During pregnancy, the mother responded to three questionnaires and the father to one. After birth, questionnaires were sent out when the child was 6 months, 18 months and 3 years old. Several sub-projects have selected participants for in-depth clinical assessment and exposure measures. The purpose of this update is to explain and describe new additions to the data collection, including questionnaires at 5, 7, 8 and 13 years as well as linkages to health registries, and to point to some findings and new areas of research. Further information can be found at [www.fhi.no/moba-en]. Researchers interested in collaboration and access to the data can complete an electronic application available on the MoBa website above., (© The Author 2016; all rights reserved. Published by Oxford University Press on behalf of the International Epidemiological Association.)

Increasing use of HRT over the last 2 decades could have contributed to the increasing incidence of cancer in women. Our aim was to investigate the relation between use of HRT and risk of hormone-dependent cancers in a Norwegian cohort of women. The Norwegian Women and Cancer (NOWAC) study is a representative, national, population-based cohort study. This report includes 35,456 postmenopausal women aged 45-64 years who answered a postal questionnaire in 1996-1998 providing information on reproduction, lifestyle and use of HRT. The women were followed up for cancer incidence. The main analyses were restricted to 31,451 postmenopausal women with complete information. Ever use of HRT was reported by 43.5% and current use, by 35% of the women. Current users had an increased risk of breast cancer (adjusted RR=2.1, 95% CI 1.5-2.5). The risk increased with increasing duration of use (ptrend < 0.0001). Using a regimen of continuous estrogen-progestagen implied an increased risk. Adjusted RRs associated with <5 and > or =5 years' duration of use were 2.6 (95% CI 1.9-3.7) and 3.2 (95% CI 2.2-4.6), respectively. The population-attributable risk of breast cancer due to current use of HRT was 27%. We found no significant increase in risk of ovarian cancer. Neither did we find users of estrogen-progestagen preparations to have any increase in risk of endometrial cancer. Our results suggest that HRT could be considered a major determinant for the increasing incidence of breast cancer in Norway.

The aim of our study was to examine the risk of breast cancer according to specific types of estrogens and progestagens in oral contraceptives (OCs) based on the prospective Norwegian Women and Cancer study (NOWAC). Between 1991-97 women aged 30-70 years were drawn at random from the central person register and mailed an invitation and a questionnaire. Women (102,443) were enrolled with follow-up information collected throughout 1999 by linkage with national registries of cancer, mortality and emigration based on the unique national identification number. Among the 96,362 women included in the present analysis 851 invasive breast cancer were diagnosed. The adjusted risk of breast cancer increased with 25% for ever use of OCs and the risk increased with increasing duration of use (test for trend: p = 0.007). No association between time since last use and breast cancer risk was found after stratification on duration of use. Positive trend was still found for total duration of use among women who used OCs more than 5 years ago. Second generation of OCs had an increased risk with increasing duration of use. Classifying progestagens according to chemical groups, the relative risk increased significantly with increasing cumulative dose of levonorgestrel progestagen. It was difficult to conclude for the other groups due to lack of power. In a multivariate analysis the cumulative dose for all progestagen groups were non-significant, although we observed a significant increased risk with increasing milligram-months of estrogen exposure (p = 0.002). In conclusion, the increased risk of breast cancer related with OC formulations could be due mostly to estrogen component., (Copyright 2003 Wiley-Liss, Inc.)