The incidence of birth has been determined for each hour of the day for all births in Norway in 1968-1977 of fetuses of 16 weeks of gestation or older, with resident mothers. The 24-hour incidence variations of births (A) with spontaneous onset and parturition, (B) with spontaneous onset, but delivery intervention, (C) with induced onset, but spontaneous birth, and (D) with induced onset and delivery intervention, are all different. It is shown that the curve for the hourly incidence of birth category A coincides very well with previous results of other workers. When multiple births are excluded and category A is split into first and later births in Northern and Southern Norway, dissimilarities arise between the respective 24-hour incidence curves. The results indicate that the 24-hour birth incidence variation has an underlying endogenous, circadian rhythmicity - possibly synchronized by the sun. The 24-hour rhythmicities of birth categories B, C and D seem to be purely exogenous - reflecting the working activity rhythms of hospital obstetricians and midwives.
In 1991, the eligibility criteria for disability benefits were restricted in Norway. Some effects are described in the present evaluation. Based on documents, first time applicants in 1990 and in 1993 in two counties were analysed according to social and medical variables. "Social security careers" before application are described, and proposals from physicians and the local social security office are compared with the decisions made by the county social security administration. Over a three-month period, applications decreased from 2.2 per 1,000 inhabitants in 1990 to 1.4 in 1993, a 39% decrease. About the same decrease was observed in all social and diagnostic groups. The proportion on vocational rehabilitation before application increased from 19% to 23% (p = 0.02). The certifying physicians proposed refusals in 9% and 8% in the two samples, and the local social security office did so in 12% and 13%. The refusal rate increased from 8% in 1990 to 21% in 1993. Refusals were mostly given to women, the middle-aged, those living alone, those with short education, and applicants with medically unclear conditions. It is pointed out that the restrictions on disability benefits in 1991 had the greatest impact on applicants with few resources.
The association between birth outcome and subsequent fertility was analyzed by using linked Norwegian birth certificates. All births of order 1, 2, and 3 which occurred during 1967 through 1974 were considered index births; there were approximately 207,000 index births of order 1, 165,000 of order 2, and 87,000 of order 3. The mothers' fertility after these index births was summarized with a life-table technique. Fertility was most pronounced if there were no survivors of an index birth, intermediate if there was one survivor, and lowest if both members of a set of twins survived. Advanced maternal age was associated with markedly reduced fertility. The sex of a surviving singleton had little effect on a mother's subsequent fertility. However, there was a sex-related difference if index twins survived; fertility was lower after the birth of unlike-sex twins and higher after the birth of like-sex twins. This probably reflects reproductive limitation rather than a differential fecundity for mothers of dizygotic and monozygotic twins. A comparison of fertility after births of like-sex and unlike-sex twins with one survivor may indicate that mothers of dizygotic twins were more fertile, but the number available for study was small. Reproduction among women who had two index births during 1967 through 1974 was examined separately. Fertility was most marked if neither of the first two infants survived and lowest where three survived (i.e., where one of the index births involved twins). If there were two survivors, the sex composition of the pair influenced fertility; fertility was greater if the two survivors were of the same sex and lower if they were of unlike sex. Since a woman who has an unfavorable outcome in one pregnancy will be at a higher risk of having an unfavorable outcome in a subsequent pregnancy, the higher fertility of such women will, to some degree, inflate the frequency of unfavorable outcomes in a population of births.
Data on parental consanguinity have been recorded for all births in Norway since 1967. Pregnancy outcome for offspring of 848 women mated to their first cousins were compared with offspring of 1,696 control women. The stillbirth rate was 23.6 per thousand for cases and 13.4 for controls. The neonatal death rate was 34.9 per thousand for cases and 14.3 for controls. The recurrence risk for sibs for early death was 9.4% for cases and 4.2% for controls. The mean offspring birth weight was significantly lower (3377 g vs. 3491 g), and the variance in birth weight was slightly larger for cases than controls. The percentage of children with malformations detected shortly after birth was 4.6% for cases and 2.2% for controls. The differences may be attributed to the increased homozygosity in offspring of first cousins. The results have relevance for genetic counselling to consanguineous couples, as well as for the understanding of the etiology of adverse pregnancy outcome and for elucidating the causes of variation in birth weight.
The increase in birth weight with parity was studied in sibships of 2, 3, and 4 children using large samples from the Norwegian Birth Registry. Families with full sibs were compared to families with maternal half-sibs. The sensitization hypothesis of Warburton and Naylor predicts no increase in birth weight with parity when the mother changes mate. The hypothesis was not supported by the data, since similar increases in birth weight with parity were found in both types of families. A small effect of the sex of the first child on the birth weight of the later born children was observed.
Accurate, unbiased malformation rates in twins must be obtained unselectively from population-based studies that include livebirths and stillbirths after a thorough ascertainment of cases. This type of study was conducted in Los Angeles County, California, where 28 twins with a neural tube defect (NTD) were identified. The prevalence in twins (1.6/1,000) was significantly higher than in singletons (1.1/1,000). The study then was expanded to include population-based data from the Medical Birth Registry of Norway which has a comparable overall NTD prevalence (1.0/1,000) and twinning rate (2%). The combined material shows a higher prevalence of anencephaly and encephalocele but not of spina bifida in twins compared to singletons. The male/female ratios in total twin and singleton cases were comparable (0.8), but varied by specific defect. Like-sex twin females appeared at highest risk for NTD as well as for fetal death. This study supports theories which associate NTDs with monozygotic twins, either through developmental disruptions that cause susceptibility to environmental agents or through a common etiology. Furthermore, it suggests that twins and singletons differ in their response to etiologic factors for the development of NTDs and that the development of each type of NTD may be related to different factors.
Basic benefit and attendance benefit to children in Norway have increased substantially in recent years. In 1992 more than 2% of children 0-15 years of age received benefits totalling NOK 350 million. The main reason for the increase seems to be that more and more children are suffering from allergic diseases, like asthma and eczema. Cohort analyses give reason to believe that allergic diseases among children will continue to increase in the years to come. Ways of dealing with the problem have recently been proposed in a publication from the health authorities. In order to evaluate the effectiveness of programmes that are implemented, a monitoring system has been suggested based on a current analysis of the prevalence of children who receive basic and attendance benefits because of allergic diseases.
OBJECTIVE: Physically demanding occupations have been associated with becoming a disability pensioner with rheumatoid arthritis (DPRA), but not with the disease of RA. The association with becoming DPRA probably reflects that patients with RA have difficulties in maintaining employment in a physically demanding occupation. However, the attitudes of the employers concerning employment of persons with RA might vary. For example, the patient's age may influence the strength of the association between a physically demanding occupation and becoming DPRA. We assessed whether the association between the predictors and becoming DPRA was stronger for the youngest or the oldest age group. METHODS: The study was prospective with data on persons in Norway 30-56 years old either in the census of 1970 or 1980. All new cases of DPRA during the 2 followup periods 1971-80 and 1981-90 were identified and analyzed by logistic regression. RESULTS: For women the predictors employment, low level of education, and period ( 1981-90 compared to 1971-80) were more strongly associated with becoming DPRA for the youngest compared to the oldest persons, while manual work and part time work were not predictors of becoming DPRA. For men, all the predictors in the study were more strongly associated with becoming DPRA for the youngest compared to the oldest age group. CONCLUSION: The higher risk of becoming DPRA was associated with most predictors for persons aged 30-39 years than the group aged 50-56 years. Our results appear to indicate that the consequences of having RA in the labor market are greater for the youngest age group.
Comparisons of birthweights of single livebirths in Hungary and Norway reveal distributions to have similar shapes; however, in the case of Hungary the distribution is shifted to the left, i.e. towards lower weights. In the registration of pregnancy outcomes, almost identical definitions are applied in the two countries, and the observed difference in distributions of birthweights is taken to reflect that Norwegian livebirths, are on average about 300 g heavier than Hungarian livebirths. Employing the method of analysis of birthweight and perinatal mortality suggested by Wilcox & Russell, it can be demonstrated that the proportions of births in the residual distributions of birthweights in the two countries are of the same magnitude and that the relative differences in first week mortality risks are similar for all birthweights. These results are taken to support the conclusion that to use a cut-off point of 2500 g in defining low birthweight, which will result in a two fold higher proportion of such infants in Hungary compared to Norway, is unwarranted, as it will falsely convey the impression of relatively more obstetric and paediatric problems in Hungary.