This study evaluates the impact of regional differences in access to intensive neonatal care on neonatal survival in geographically defined populations of 4,692 low birthweight births in Norway 1979-81. For infants weighting 1,250 to 2,499 g our results are consistent with the existence of a dose-response association between neonatal survival and the level of immediate access to intensive neonatal care. Although not statistically significant, there was a clear gradient in the risk of mortality within 24 hours. A similar pattern of survival could not be consistently demonstrated for infants weighing less than 1,250 g.
In order to estimate the association between intrauterine growth and childhood survival, data on birth weight and gestational age from the Norwegian Birth Registry, for all children who survived the first year of life and who were born during the period 1967-1989 were linked to the National Cause of Death Registry for the period 1968-1991. Deaths were categorized into five cause of death groups: malformations, cancer, infections, accidents, and other causes. The adjusted relative risk of death from all causes at ages 1-5 years was 2.18 (95% confidence interval (CI) 1.85-2.56) for children with birth weight or = 2,500 g. For ages 6-10 years, the corresponding adjusted relative risk (95% CI) was 1.83 (1.35-2.48), and for ages 11-15 years, it was 1.35 (0.91-1.99). Death from infections, accidents, and other causes showed a reversed J-shaped association with birth weight, while malformations showed a log-linear decrease in mortality with increasing birth weight. For cancer deaths, low birth weight showed an opposite association. The association between birth weight and childhood mortality is complex, and cause-specific analyses are necessary to understand the connection between intrauterine influences and later mortality.
OBJECTIVE: To describe birthweight by gestational age in Norway for the period 1967-1998, evaluate secular trends and provide new standards for small for gestational age for 16 to 44 weeks of gestation. SUBJECTS AND METHODS: The analyses were based on more than 1.8 million singleton births, covering all births in Norway for a 32 year period. Percentiles for birthweight by gestational age were estimated using smoothed means and standard deviations. In the preterm weeks, means and standard deviations were carefully screened for birthweight-gestational age consistency, adapting a method of Wilcox and Russell. Differences in birthweight by gestational age for stillbirths and livebirths in extremely preterm weeks (16-28) are presented, and the effects of cesarean section are evaluated. We observed a clear increase in birthweight by gestational age for all term weeks, but a decrease for most of the preterm weeks over the same period. This decrease was related to the increase in deliveries by cesarean section. CONCLUSIONS: Percentiles for birthweight by gestational age are presented for clinical use, based on a current period 1987-98, covering 20-44 completed gestational weeks. In the final standards we excluded stillbirths, infants born with malformations and cesarean sections. Birthweights in the Scandinavian populations are high and standards from other populations may not be representative, especially for the term weeks. Also, the secular changes demonstrated in this study indicate that old birthweight by gestational age standards need revision, especially due to changes in obstetrical routines influencing preterm data.
At low birth weight the variance of last menstrual period based gestational age is wide and the distribution is positively skewed toward higher values. In this study the variance of gestational age decreases rapidly as birth weight increases, skewness decreases and kurtosis increases in approaching the mean of the birth weight distribution. Some of the wider variance and positive skewness of gestational age at low birth weight appears to reflect heterogeneity of intrauterine growth, in which infants with high values of gestational age are growth retarded. We show by partitioning each birth weight group into two groups of infants with different gestational age distributions, that at low birth weight, infants with low gestational ages have higher neonatal mortality rates but lower fetal mortality rates than infants with a higher gestational age for birth weight. The differences in mortality described between small infants at different gestational ages suggest that infants with a high LMP-based gestational age have experienced a slower rate of intrauterine growth. Some authors interpret the distributional characteristics as indications of systematic error in last menstrual period based assessment of gestational age. It appears from this study that the extent of systematic error in the estimation of LMP based gestational age may have been overstated in the past.
BACKGROUND AND METHOD: Small-for-gestational-age (SGA) infants represent a heterogeneous group of normal and growth-retarded children. To assess the familial aggregation of reduced fetal growth, birth weights in both maternal and paternal relatives of 1246 index children in the Scandinavian SGA Study were compared across groups defined by the SGA outcome of the index child as well as that of earlier siblings. RESULTS: Mean maternal birth weight +/- SEM was 3127 +/- 54 g for mothers who had experienced two SGA births as opposed to 3424 +/- 22 for mothers with no SGA births. Mean paternal birth weight was 3497 +/- 88 g and 3665 +/- 24 in the same two groups. The odds ratio (with 95% confidence interval) for having a mother with birth weight below the 10th percentile was 1.74 (0.85-3.58) for the group where two SGA births had occurred compared to no SGA births and it was 2.49 (1.22-5.07) for having a father with birth weight below the 10th percentile. There was no correlation between maternal and paternal birth weights. CONCLUSIONS: The association also to paternal birth weight suggests the presence of genetic or common environmental factors in explaining the tendency to have SGA children. Although taking parental birth weights into consideration will aid in diagnosing growth-retardation in a SGA child, SGA remains a heterogeneous group where familial and non-familial cases will be difficult to separate.
Percentiles of weight-by-gestational age were constructed for first and second births, based on linked sibship-data from the Medical Birth Registry of Norway. Standards were made for weight-by-gestational age of second births conditional on whether the first birth was small-for-gestational age (SGA) or large-for-gestational age (LGA). These standards were compared with the conventional, cross-sectional standard of all second births. The relevance of the conditional standards was assessed on the basis of perinatal mortality, using logistic regression analyses. When applying cross-sectional standards of second births, more than 30% of the births following a SGA first birth were classified as SGA, compared with only 1.7% following an LGA first births. The overall risk for a perinatal loss in second births following a SGA first birth was twice that among second births following a LGA first birth. When second births were themselves categorised as SGA or non-SGA using the cross-sectional standards, the mortality among the SGA second births was such that the risk was 4 to 5 times higher following LGA first births compared with SGA first births. When conditional standards were applied to define SGA among second births, the risk relation between the subgroups (defined by classification of first birth) corresponded to the observed overall risk pattern. An unconditional SGA classification conceals important differences between clinically distinct subgroups.
The relationship between living in a physical abusive relationship and adverse outcome of pregnancy was examined using a structured interview including an obstetrical history. Sixty-six women living in a physically abusive relationship, and 114 women randomly selected and not presently living in such a relationship were interviewed. The women reported 312 completed pregnancies. Five of these were twin pregnancies and one was a stillbirth without information on birth weight. Of the 306 pregnancies included in the analysis, violence had occurred in 40. The mean birth weight of births reported by women exposed to violence during pregnancy was 229 g less than the equivalent figure in non-exposed pregnancies. Adjustment for education, primiparity, and history of addiction reduced the difference in mean birth weight to 175 g.
This article describes a study of the relationship between diet and smoking in a group of 821 Norwegian pregnant women. The study is part of a multi-centre project, examining risk factors for intrauterine growth retardation. Two 3-day dietary records were collected during the 17th and 33rd week of pregnancy. Information on smoking habits and other relevant parameters were collected through an extensive questionnaire. The results showed that the smokers consumed significantly less than the non-smokers of bread, cakes and cookies, vegetables, fruits and berries, cheese, yoghurt, low fat milk, juice and tea. The smokers also consumed significantly more meat, margarine, whole milk, soft drinks and coffee than the non-smokers on both occasions. The diet of the smokers contained significantly less protein, carbohydrate, dietary fibre, thiamin, riboflavin, vitamin C, calcium and iron as compared with the non-smokers. Fat contributed significantly more to the energy content of the diet of the smokers and it is concluded that their diet was less nutritious than that of the non-smokers throughout pregnancy.