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We studied mean changes in birthweight from the first to the second delivery according to length of the inter-pregnancy interval. We also studied recurrence risk of low birthweight, preterm birth and perinatal death. We followed all women in Norway from their first to their second singleton delivery at gestational week 22 or beyond during the years 1970-2019, a total of 654 100 women. Data were obtained from the Medical Birth Registry of Norway. Mean birthweight increased from the first to the second delivery, and the increase was highest in pregnancies conceived < 6 months after the first delivery; adjusted mean birthweight increase 227 g (g) (95% CI; 219-236 g), 90 g higher than in pregnancies conceived 6-11 months after the first delivery (137 g (95% CI; 130-144 g)). After exclusion of women with a first stillbirth, the mean increase in birthweight at inter-pregnancy interval < 6 months was attenuated (152 g, 95% CI; 143-160 g), but remained higher than at longer inter-pregnancy intervals. This finding was particularly prominent in women > 35 years (218 g, 95% CI; 139 -298 g). In women with a first live born infant weighing < 2500 g, mean birthweight increased by around 1000 g to the second delivery, and the increase was most prominent at < 6 months inter-pregnancy interval. We found increased recurrence risk of preterm birth at inter-pregnancy interval < 6 months, but no increased recurrence risk of low birthweight, small for gestational age infant or perinatal death. In conclusion, we found the highest mean increase in birthweight when the inter-pregnancy interval was short. Our results do not generally discourage short pregnancy intervals.

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We examined whether the fertility pattern of immigrant mothers is handed down to the next generation. Our analyses were carried out on population register data. These data contained information on all immigrants to Norway from 123 countries during the period 1935-1995. We examined whether there was a relationship between the fertility rate in the country of origin and the number of children for generations 1.5 and 2 in Norway. We estimated three models: fixed effects for country of origin, fixed effects for region, and no fixed effects. The three specifications yielded estimates with overlapping confidence intervals. We interpret the estimates from the models with fixed effects for region, and the model with no fixed effects as upper-bound estimates. They show that an increase of 1.00 in the fertility rate in the country of origin leads to an average increase in the number of children of 0.12 (no fixed effects) or 0.14 (fixed effects for region) for immigrant women in generations 1.5 and 2. The estimate from the model with fixed effects for country of origin was small and not statistically significant at the conventional level. We interpret this as a lower-bound estimate. Our upper-bound estimates for generations 1.5 and 2 are smaller than the estimates for generation 1, i.e. there has been a decrease in the fertility rate from the first to the second generation. As a result, if the proportion of the population with an immigrant background continues to increase, it may increase at a slower rate in the future.

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OBJECTIVE: An important part of Norwegian welfare policy is to provide subsidized orthodontic treatment for children and adolescents. The objective of this policy is that dental services should be allocated according to children's need for treatment, and not according to parents' ability to pay. The probability of receiving orthodontic treatment independent of parent's household income was examined. METHODS: The study population encompassed children and adolescents aged 10-18 years in 2019 (n = 354 439). Information about whether they had started orthodontic treatment was obtained from the Norwegian Health Economics Administration. The key independent variable was net equalized household income. Inequalities were measured using concentration indices, which were estimated according to the severity of the malocclusion (very great need, great need, obvious need and no need). Two indices were used to measure relative inequality: the unstandardized concentration index and the partial concentration index. Absolute inequality was measured using the corrected concentration index. Relevant control variables were included in some of the analyses. RESULTS: The unstandardized indices were in the range 0.04 (very great need) to 0.05 (obvious need). For all three groups of severity, the 95% confidence intervals overlapped. The values of the partial indices were significantly lower than the values of the unstandardized indices. The partial indices were in the range 0.008 (very great need) to 0.03 (obvious need). The 95% confidence intervals for the partial indices did not overlap with the 95% confidence intervals of the unstandardized indices. For all three groups of severity, the indices that measured absolute inequality were close to zero. CONCLUSIONS: It is possible to achieve the egalitarian aim of equality in service provision by subsidizing orthodontic treatment. This is possible within a system where the cost of orthodontic treatment is reimbursed according to the criteria of need. These criteria function in such a way that patients with the greatest need for orthodontic treatment are given the highest priority.

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INTRODUCTION: We studied changes in placental weight from the first to the second delivery according to length of the inter-pregnancy interval. METHODS: We followed all women in Norway from their first to their second successive singleton pregnancy during the years 1999-2019, a total of 271 184 women. We used data from the Medical Birth Registry of Norway and studied changes in placental weight (in grams (g)) according to the length of the inter-pregnancy. Adjustments were made for year and maternal age at first delivery, changes in the prevalence of maternal diseases (hypertension and diabetes), and a new father to the second pregnancy. RESULTS: Mean placental weight increased from 655 g at the first delivery to 680 g at the second. The adjusted increase in placental weight was highest at inter-pregnancy intervals <6 months; 38.2 g (95 % CI 33.0g-43.4 g) versus 23.2 g (95 % CI 18.8g-27.7 g) at inter-pregnancy interval 6-17 months. At inter-pregnancy intervals ≥18 months, placental weight remained higher than at the first delivery, but was non-different from inter-pregnancy intervals 6-17 months. Also, after additional adjustment for daily smoking and body mass index in sub-samples, we found the highest increase in placental weight at the shortest inter-pregnancy interval. We estimated no difference in gestational age at delivery or placental to birthweight ratio according to inter-pregnancy interval. DISCUSSION: Placental weight increased from the first to the second pregnancy, and the increase was most pronounced at short inter-pregnancy intervals. The biological causes and implications of such findings remain to be studied.

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AIM: Tooth loss studies show that periodontal treatment is effective. However, it is not known whether these results can be projected into a lifetime of treatment. The aim of the study was to study all patients with stages III/IV of periodontitis over 30 years in a private practice. MATERIALS AND METHODS: All patients referred between 1986 and 1990 were monitored for 30 years for tooth loss and prognostic factors. All dropouts were accounted for. RESULTS: In all, 386 patients were followed, of whom 283 patients dropped out, leaving 103 patients (67 females and 36 males, average age 40.1 years) monitored over 30 years. Tooth loss was stable until 16 years, when the population was divided into groups of low (n = 65), moderate (n = 18) and high (n = 20) tooth loss, losing 1.05 (SD 1.27), 4.83 (SD 0.96) and 11.90 (SD 4.25) teeth, respectively. The strongest prognostic factors were first-degree relatives with periodontitis, periodontal treatment before the age of 35 years, diabetes and patients with teeth with initial hopeless prognosis. CONCLUSION: The majority of patients with stages III and IV periodontitis could be successfully treated with conventional periodontal treatment over a period of 30 years. The findings suggest that retrospective studies with shorter observation times cannot automatically be projected onto the outcome of a lifetime of periodontal treatment.

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OBJECTIVE: In Norway, supply of dental services exceeds demand, mainly because of the marked improvement in dental health during the last few decades. The aim of the study was to investigate whether private dental practitioners counteract a fall in demand for their services by providing more services or by raising their fees. METHODS: The data were collected using a questionnaire that was sent to all private dental practitioners in Norway. Altogether 1237 practitioners responded, which gave a response rate of 56%. Our sample was representative of the population of practitioners in Norway. As a measure of patient supply, responses from the following questions were used: 'Based on an overall assessment of economy, workload and other personal factors, is the number of regular patients adequate? If not, do you wish to have more patients, or fewer patients?' The outcome variables were dental fees, length of recall interval and mean cost per visit. The data were analysed using ordinary least square regression and a linear probability model. The following characteristics of the private dental practitioners were included as control variables: age, gender, work experience in years and whether they worked in a solo practice. To test the robustness of the findings, a supplementary analysis with the patient as the unit of analysis was carried out, using survey data of Norwegians aged 20 years and older. Based on this survey, the relationship between population: dentist ratio and mean cost per dental visit were examined. RESULTS: Nearly 40% of all practitioners reported that they had too few patients. They compensated for their loss of income by raising their fees, by recalling their patients more often and by increasing the cost per visit. The finding in the supplementary analysis using survey data from patients was similar to the findings in the main analyses using survey data from private dental practitioners. CONCLUSION: The findings show that practitioners have market power. They were able to counteract a fall in demand for their services by providing more services and by raising their fees. The dental profession should be encouraged to provide appropriate services, in the present situation where supply exceeds demand.

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INTRODUCTION: ST segment analysis (STAN) of the fetal electrocardiogram was introduced as an adjunct to cardiotocography for intrapartum fetal monitoring 30 years ago. We examined the impact of the introduction of STAN on changes in the occurrence of fetal and neonatal deaths, Apgar scores of <7 at 5 min, intrapartum cesarean sections, and instrumental vaginal deliveries while controlling for time- and hospital-specific trends and maternal risk factors. MATERIAL AND METHODS: Data were retrieved from the Medical Birth Registry of Norway from 1985 to 2014. Individual data were linked to the Education Registry and the Central Person Registry. The study sample included 1 132 022 singleton births with a gestational age of 36 weeks or beyond. Information about the year of STAN introduction was collected from every birth unit in Norway using a questionnaire. Our data structure consisted of a hospital-year panel. We applied a linear probability model with hospital-fixed effects and with adjustment for potentially confounding factors. The prevalence of the outcomes before and after the introduction of STAN were compared within each birth unit. RESULTS: In total, 23 birth units, representing 76% of all births in Norway, had introduced the STAN technology. During the study period, stillbirths declined from 2.6 to 1.9 per 1000 births, neonatal deaths declined from 1.7 to 0.7 per 1000 live births, babies with Apgar score <7 at 5 min after birth increased from 7.4 to 9.5 per 1000 births, intrapartum cesarean sections increased from 6.4% to 9.5%, and instrumental vaginal deliveries increased from 7.8% to 10.9%. Our analyses found that the introduction of STAN was not associated with the decline in proportion of stillbirths (p =0.76) and neonatal deaths (p =0.76) or with the increase in intrapartum cesarean sections (p =0.92) and instrumental vaginal deliveries (p =0.78). However, it was associated with the increased occurrence of Apgar score <7 at 5 min (p =0.01). CONCLUSIONS: There is no evidence that the introduction of STAN contributed to changes in the rates of stillbirths, neonatal deaths, intrapartum cesarean sections, or instrumental vaginal deliveries. There was an association between the introduction of STAN and a small increase in neonates with low Apgar scores.

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BACKGROUND: The aim of the present study was to examine the effect that the introduction of Doppler ultrasound in obstetric care has had on fetal death in Norway. One mechanism by which Doppler ultrasound may reduce fetal death may be through the increased use of Caesarean delivery. Therefore, we also examined the effect that the use of Doppler ultrasound has had on the use of Caesarean delivery. METHODS: The Medical Birth Registry of Norway provided detailed medical information for ∼1.2 million deliveries from 1990 to 2014. Information about the year of introduction of Doppler ultrasound was collected directly from the maternity units, using a questionnaire. The data were analysed using a hospital fixed-effects regression model with fetal death as the outcome measure. The key independent variable was the introduction of Doppler ultrasound at each maternity ward. Hospital-specific trends and risk factors of the mother for fetal death were included as covariates. RESULTS: For pre-term deliveries, the introduction of Doppler ultrasound contributed to a reduction in fetal death of ∼30% and to an increase in planned Caesarean section of ∼15%. There were no effects for emergency Caesarean sections or inductions pre-term. The introduction of Doppler ultrasound had no effect on fetal death or Caesarean section for term deliveries. CONCLUSIONS: The introduction of Doppler ultrasound during the 1990s and 2000s made a significant contribution to the decline in the number of pre-term fetal deaths in Norway. Increased use of Caesarean section may have contributed to this reduction.

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OBJECTIVES: There has been a marked improvement in dental health in Norway during the last few decades. What effect has this had on provision of dental services, and how has private dental practitioners' assessment of their workload changed? METHODS: The data were from 2 large surveys of private dental practitioners carried out in 1992 (n = 1056) and 2015 (n = 1237). An analysis of nonresponders showed that they were evenly distributed according to their age, gender, and the region in which their practice was located. Thus, the samples were representative of private dental practitioners. For 1 representative week in practice, the practitioners were asked to report the number of visits and the number of patients who received 1 or more of the following items of treatment: filling, crown, bridge, denture, root filling, extraction, and periodontal treatment. As a measure of patient supply, the responses from the following questions were used: "Based on an overall assessment of economy, workload, and other personal factors, is the number of regular patients adequate? If not, do you wish to have more patients or fewer patients?" RESULTS: From 1992 to 2015, the annual number of visits per practitioner decreased by 23%. The number of patients per practitioner who received fillings, crowns, bridges, dentures, root fillings, or extractions decreased by 50% or more. The decrease was largest for practitioners younger than 35 years and for men. The proportion of practitioners who reported a deficit of patients increased from 20% to 37%. CONCLUSIONS: Many dentists will have too few patients and a fall in income in the years to come is expected.

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OBJECTIVE: The assessment of the success of conventional periodontal therapy is based on retrospective studies from private practice and university clinics. Due to their marked heterogeneity, it is difficult to assess the data quality and rate these studies. The aim is to test a model for auditing and rating the data quality of periodontal outcome studies. METHODS: The method was adapted from the NIH Health Care Systems Collaboratory model, which uses three data quality dimensions: completeness (including all the relevant variables), consistency (ensuring that the same variables are compared) and accuracy (proportion of data in error with a gold standard). The model was applied to studies from a Norwegian specialist practice and data from the Norwegian Health database to test if the auditing process was workable using real world data. RESULTS: Forty-seven risk and prognostic factors were included for completeness. Seven variables were specified for consistency: tooth loss, smoking, systemic conditions, oral hygiene, individual tooth prognosis, maintenance profiles and timing of extractions. The factors tested showed a 95.7% completeness and an average accuracy deviation from the gold standard of -2.3% for each of the risk/prognostic factors and an overall study score of 93.3%. CONCLUSIONS: It was possible to develop a method for auditing and rating the quality of periodontal outcome studies. The model was tested using both real world data including risk and prognostic factors from individual outcome studies and national big data. The application of the model to these sets of data showed a high accuracy of the risk/prognostic factors and a close relationship with national big data.

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OBJECTIVES: Equality in access to dental services, independent of level of education, is an important aim of Scandinavian welfare policy. In Norway, this policy is the main justification for a dental public subsidy scheme for adults. An important part of the subsidy scheme is to cover the cost of fixed prosthodontic treatment, including implant-based crowns and bridges for premolars, canines and incisors. A stated policy goal is to secure equal access to everybody in need of these services, independent of their level of education. The aim of this study was to estimate the causal effect of education on the probability of receiving fixed prosthodontic treatment in the adult Norwegian population. METHODS: During the period 1960-1972, all municipalities in Norway were required to increase the number of compulsory years of education from seven to nine years. We used this education reform as the instrumental variable to create exogenous variation in the individual's number of years of education. The education data were combined with data from the Norwegian Health Economics Administration, which contained our outcome variable. Our sample included individuals with 9 years education or less. Altogether 113 237 individuals were included in the study. RESULTS: For men, the first stage regression coefficient was 0.87 (confidence interval: 0.82-0.92). This means that the reform resulted in 0.87 additional years of education. For men, the probability of receiving fixed prosthodontic treatment increased by 0.67 percentage points per additional year of schooling. For women, the first stage regression coefficient was 0.84 (confidence interval: 0.79-0.88). The second stage regression coefficient was small (= 0.0022) and not statistically significant at a conventional level. CONCLUSION: From a welfare policy point of view, for men, the subsidy scheme has not succeeded to redistribute resources so that dental services are accessible independent of their social status.

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BACKGROUND: Epidemiological studies have reported high levels of periodontal diseases worldwide. Over the last 40 years, Norway has introduced several measures including major financial support to reduce periodontal diseases. The aims of this study were to establish the present level of periodontal treatment, the treatment profiles for the nation, and to assess if long-term clinical data support the findings. MATERIALS AND METHODS: The database of the Norwegian Health Economic Administration for 2013 was analysed to establish the prevalence of treated periodontitis in a cross-sectional register-based study. Treatment profiles including patients' ages, gender, geographic distributions, treatment types, prosthetic tooth replacements and the treatment distributions between the dental health professionals were assessed. RESULTS: 4.4% of the 20 years and older age group was treated for periodontitis. More females (55%) than males (45%) were treated with predominance in the 60-69 year age group. Private general dental practitioners performed 43.8% of the total periodontal treatment, while dental hygienists performed 22.5%. Periodontists performed 32.8% of the non-surgical and 74.6% of the surgical treatment. Tooth replacements for teeth lost due to periodontal diseases were provided for 0.57% of the population. Clinical studies from Norway showed marked improvements in the periodontal parameters examined over the last 40 years. CONCLUSION: The frequency of periodontal treatments in Norway was low, but sufficient to maintain major tooth retention for the population. Long-term external clinical data supported these findings. The treatments were well distributed between private general dental practitioners, hygienists and periodontists.

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AIM: Little evidence exists on how familial tendencies affect the long-term success of periodontal therapy. The aim of this study was to compare outcomes for two generations and their control patients treated in the same private practice. MATERIALS/METHODS: Parents and their children were observed for tooth loss between 1986 and 2017. Matching control groups were identified from the same practice, one for the parent and one for the children group. The control patients had no close family members with a history of periodontal diseases. Both the generations and control groups completed a similar course of periodontal therapy. The matching strategy aimed at making the groups as similar as possible with respect to well-known risk and prognostic factors. The data were analysed by multiple regression where the outcome was the number of teeth lost due to periodontal disease. RESULTS: A total of 435 patients were identified (148 parents, 154 children and 133 controls). 72 parents and 61 children (133) had more than 5 years follow-up (average 15.5 and 12.9 years, respectively). Balancing tests showed that the matching was successful. 65% of tooth loss was attributable to close family history. The regression showed that the parent generation lost 1.02 more teeth than the controls, while the children lost 0.61 more teeth. CONCLUSION: Having close family members with a history of periodontal diseases is a strong prognostic factor affecting the long-term outcome of periodontal therapy.

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INTRODUCTION: We aimed to estimate differences in offspring birthweight and placental weight between Norwegian women and immigrants in Norway from countries with armed conflicts. We also studied whether length of residence in Norway was associated with offspring birthweight and placental weight. MATERIAL AND METHODS: We included in our study all singleton births in Norway at gestational week 28 or beyond during the years 1999-2014, to mothers who were born in Somalia, Afghanistan, Iraq (total immigrants n = 18 817), or Norway (n = 668 439). Data were obtained from The Medical Birth Registry of Norway and the Central Person Registry of Norway. We estimated the differences between Norwegian and immigrant women in mean offspring birthweight and mean placental weight by applying linear regression analyses. Adjustments were made for maternal age, parity, year of delivery, gestational age at delivery, preeclampsia, and diabetes. RESULTS: The immigrant women had 206 g (95% CI 199 to 213 g) lower mean offspring birthweight and 16 g (95% CI 14 to 18 g) lower mean placental weight than Norwegian women. Immigrant women with ≥5 years of residence in Norway had higher offspring birthweight (40 g) and higher placental weight (17 g) than immigrant women with <5 years of residence. CONCLUSIONS: Immigrant mothers from Somalia, Afghanistan, and Iraq gave birth to infants and placentas with lower weight than Norwegian women. However, the difference between Norwegian women and immigrant women was reduced by length of residence in Norway.

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We estimated the effects of education on mortality and causes of death in Norway. We identified causal effects by exploiting the staggered implementation of a school reform that increased the length of compulsory education from seven to nine years. The municipality-level education data were combined with complete records of all deaths from 1960 to 2015 from the Norwegian Cause of Death Registry. These data covered the entire life span of persons aged 16-64. One additional year of education caused a reduction in mortality of about 10% for men. The effect was negligible for women. For men, a large part of the effect was due to fewer accidental deaths. We suggest two explanations for this finding. First, there are differences in risk-taking behaviour between people with a high level of education and those with a low level. Second, more education leads to upward occupational mobility. This mobility is mainly from occupations for which the risk of accidents is high to occupations for which the risk is low. Our results supported the fundamental cause theory. This is because education had a stronger effect on mortality for causes of death that are preventable than for causes of death that are not preventable. More education had no effect on the probability of dying of diseases that were amenable to medical intervention only. This gives some support to our results that patients are treated equally, independent of their level of education. This may be due to the large public involvement in financing and provision of health services.

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BACKGROUND: In Norway, for several dental conditions, a substantial part of treatment costs are reimbursed by the National Insurance Scheme. Ideally, the probability of receiving subsidized dental care (SDC) should be independent of social determinants of health, such as education, so that dental services are accessible to everyone independent of their social status. OBJECTIVE: The main objective of this study was to estimate the causal effect of education on the probability of receiving SDC in the adult Norwegian population. RESEARCH DESIGN: During the period 1960-1972, all municipalities in Norway were required to increase the number of compulsory years of education from 7 to 9 years. This education reform was used to create exogenous variation in the education variable. Since municipalities implemented the reform at different times, we have both cross-sectional and time series variation in the reform instrument. Thus we were able to estimate the effect of education on the probability of receiving SDC by controlling for municipality fixed effects and trend variables. SUBJECTS: This study included all Norwegian adults, born during the period of 1947-1958. MEASURES: Information about education (number of years), whether the individuals had received SDC, place of residence (municipality) was collected. RESULTS: The probability of receiving SDC was found to increase by 2 percentage points per additional year of education. CONCLUSION: People with the most resources benefit the most from a universal welfare scheme that is addressed to reach everybody. We suggest providing information about the subsidy scheme in a way that is easily available and understandable to all individuals, independent of their level of education.

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