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Biomedical subjects

T Bjerkedal

Publications and source records attributed to T Bjerkedal.

At least 73 records · Page 4Linked to original sources
PubMed1985

Association of parental consanguinity with decreased birth weight and increased rate of early death and congenital malformations.

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.

Birth Weight↗
PubMed1985

The heritability of smoking behaviour in pregnancy, and the birth weights of offspring of smoking-discordant twins.

Questionnaire information on smoking habits in pregnancy was collated in 341 monozygotic (MZ) and 321 dizygotic (DZ) female twin pair cases from a population-based Norwegian Twin Panel. In a multifactorial model, the intra-pair correlation in smoking was 0.797 (+/- 0.042) in monozygotic (MZ) and 0.443 (+/- 0.075) in dizygotic (DZ) twin pairs, indicating a substantial genetic influence on liability to smoke in pregnancy. The questionnaire information was linked with birth records in the Medical Birth Registry of Norway, and birth weights of offspring of 62 MZ and 100 DZ smoking-discordant twin pairs were studied. Offspring of smoking MZ twins weighed 127 g less than birth order matched offspring of the non-smoking co-twins. This finding is additional evidence that smoking is a direct cause of reduced birth weight in offspring.

Birth Weight↗
PubMed1984

Malformations in twins and their siblings, Norway, 1967-79.

During 1967-79 the population-based Medical Birth Registry of Norway registered 7,660 twin pairs (1% of births) born to 7,596 mothers, who gave birth to 6,608 additional infants (twin siblings). The total rate of malformations among twins (278.1/10,000) was not significantly different than among singletons (302.1/10,000), nor among twin siblings (314.8/10,000). By specific type of defect, twins had significantly higher rates than singletons of central nervous system (CNS) defects (Rate Ratio = 1.8) and cardiovascular defects (RR = 1.5). The twins also had a significantly low rate of congenital hip dislocation (RR = 0.4), which may explain the relatively low incidence of malformations in twins. Like-sex (LS) twins had a slightly higher rate of malformations than unlike-sex (US) twins (RR = 1.1), as well as a higher rate of CNS defects (RR = 3.0). The siblings also had a significantly increased rate of CNS defects compared to singletons (RR = 1.9), but not of cardiovascular defects (RR = 0.9). The results indicate that twins have elevated rates of at least some congenital malformations. The observations about CNS defects suggest common factors that can lead to either like-sex twinning, CNS defects, or both. The increased frequency of cardiovascular defects in twins appears to be associated with the biologic conditions of twinning.

Adult↗
PubMed1984

Parental determinants of birth weight.

As part of a study on causes of variation in birth weight, questionnaire data on parental measures were related to offspring birth weights recorded in the Medical Birth Registry of Norway. A genetic analysis of parent-offspring covariances in birth weight indicated that about 60% of the variance in birth weight could be explained by effects of fetal genes, while no effects of maternal genes were detectable. Multiple regression analysis showed that height and weight of both parents and maternal smoking status were associated with variation in birth weight. Socioeconomic status, educational attainment and paternal smoking habit had no independent effects. The adult, parental variables could only explain 10% of the variation in mean offspring birth weight.

Birth Weight↗
PubMed1983

Association of birth outcome with subsequent fertility.

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.

Adolescent↗
PubMed1983

The 24-hour rhythmicity of birth. A populational study.

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.

Circadian Rhythm↗
PubMed1982

Fetal and infant mortality in Norway and the United States.

Relative to the countries of northern Europe, the United States has a high crude infant mortality rate. We compared the United States' fetal and infant mortality rates with those of Norway, a nation tht is internationally recognized for having a low infant mortality. Norwegian birth-weight-specific rates were applied to the US birth populations, yielding adjusted rates. The adjusted rates, which are the crude rates that would have resulted in the United States if the Norwegian birth-weight-specific rates had been in force, were generally higher than the US rates that were actually observed. Thus, the major reason for the United States' poor international rank is probably its unfavorable birth-weight distributions, and any major improvement in the United States' international standing will likely await a reduction in the proportion of high-risk, low-weight births.

Adult↗
PubMed1982

The association of twinning and neural tube defects: studies in Los Angeles, California, and Norway.

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.

California↗
PubMed1982

Secular trends of neural tube defects by demographic subgroups in Norway, 1967-81.

The secular trends of NTDs by subgroups were investigated using data from the population-based Medical Birth Registry of Norway. During 1967-81, rates of total congenital malformations significantly increased by 4.1% annually. In contrast, there was an average annual decline of 1.6% in anencephaly rates and 0.4% in spina bifida rates. Annual rates of NTDs among twins decreased more (3.8%) than among singletons (1.6%). Females had an annual decline in rates (2.2%) that was greater than in males (0.7%). Separation of NTDs into two sub-groups based on the presence of multiple major malformations, revealed a significant decline of 2.1% annually in singles, whereas rates in multiples showed an increase of 3.3% annually. The different prevalence patterns revealed in various subgroups strongly suggest different etiologic entities. These should be further refined for elucidating etiologic factors. Furthermore, in prediction of current cases and evaluation of the effects of health services, the proportion of the various subgroups present should be considered.

Anencephaly↗
PubMed1980

Outcome of pregnancies in diabetic mothers in Norway 1967-1976.

A total of 1035 births to diabetic mothers were registered in Norway during the 10-year period 1967-1976. Perinatal mortality (from 16 weeks of gestation until 7 days after birth) decreased from 177.4 per 1000 births in 1967-68 to 60.7 in 1975-1976; for the total population the figures were 24.1 and 18.4. During the same period the duration of gestation increased from 35.5 weeks in 1967-1968 to 37.0 weeks in 1975-1976. The numbers of small and large infants decreased: in 1967-1968 53.3% weighed 2500-4000 grams, in 1975-1976 70.7%. Moreover, more births took place in university clinics and regional hospitals, 38.7% in 1967-1968 and 77.1% in 1975-1976. Malformations were 50% more common in children of diabetics. Cardiovascular and nervous system malformations accounted for this increase, being 5 times more frequent than in the general population.

Birth Weight↗