Pregnancy and delivery outcomes in Norway the past five decades; associations with Maternal country of birth, Socioeconomic status and Regional differencies

Data from the Norwegian Medical Birth Registry (MBRN) show a higher incidence of perinatal mortality among non-European immigrant women compared to Norwegian or other European women giving birth in Norwegian hospitals. The risk of perinatal mortality is doubled among women from Sub-Saharan Africa and notably increased among women from the Middle East and North Africa compared with women born in Norway. The reasons for this dramatic difference are unknown and presumably complex. Such significant differences indicate an urgent need for in-depth investigation with the aim to reduce these differences between ethnicities as a whole, as well as to improve the total outcome for all women delivering in Norway. 

The PURPLE Study will explore the main adverse perinatal outcomes in relation to maternal country of birth and immigrant status: 

1. Perinatal mortality and morbidity, preterm birth, fetal growth restriction.
2. Maternal morbidity: preeclampsia, overweight and obesity, diabetes.

All these outcomes affect offspring’s health later in life, linking perinatal health research to public health issues.

3. Inequality in health: Norwegian Medical Birth Registry shows notable differences between regions in Norway. This can cause inequality in the provided health care and needs to be studied.

Large studies exploring the complex associations between maternal country of origin, socioeconomic status, education level, comorbidity and adverse pregnancy outcomes are lacking. The PURPLE study is unique in its approach to fill in this knowledge gap using data obtained from MBRN and Statistics Norway (SSB), with more than 2.8 million deliveries. The data set comprises extended information on the women giving birth and their offspring. 

The study will provide novel information on how pre-pregnancy factors and pregnancy complications affect pregnancy outcome, with major implications for individual, family as well as public health.

Results from this study will be used to update national guidelines on antenatal and perinatal care, to improve and individualize antenatal health care offered to women with high risk pregnancy. The study results will help to reduce health inequality between individual and regions in Norway.

The PURPLE Study is a population-based epidemiological study, aiming to assess adverse pregnancy outcomes and relation to maternal country of birth, socioeconomic differences, and regional differences in Norway. 

The PURPLE study is a register study based on data from two large population registries. Data from MBRN and SSB are merged, a unique design that allows us to test complex associations and explanations for adverse pregnancy outcomes. 

To study associations between outcomes and exposures, both multivariate and multilevel analysis will be used. In addition to descriptive statistics, differences between the groups (immigrants vs. non-immigrants) will be evaluated by a chi-square test for categorical variables and Student’s t-test for continuous variables. Analysis of variance will be used when more than two groups are compared. Non-parametric methods will be used when appropriate. 

To identify variables being significantly associated with a chosen outcome, adjusting for potential confounding factors, a multivariate analysis will be performed. Regression analysis such as logistic, linear or Poisson distribution will be used, dependent on the outcome studied. To consider dependencies in data (i.e., clustering within country or residence at time of birth and obstetric practices) Generalized Estimating Equations (GEE) models or mixed models will be used. The data will be analyzed by the statistical software packages SPSS and Stata.