OBJECTIVE: This study was undertaken to provide new standards for birth weight according to gestational age through the addition of family data on maternal birth weight and birth weights of previous siblings. STUDY DESIGN: The analyses were based on 1.7 million births in Norway from 1967 through 1998. These population data were arranged into sibships and mother-offspring units through unique personal numbers. We categorized first births by sex and maternal birth weight and second births by sex and birth weight of the older sibling. RESULTS: Standards for birth weight per gestational age percentiles differed by >1100 g when the birth weight of an older sibling was considered and by almost 700 g when maternal birth weight was considered. The value of these new standards for birth weight according to gestational age was demonstrated through variation in perinatal mortality. CONCLUSION: Maternal birth weight and birth weights of previous siblings allow improved predictions of birth weight according to gestational age and should be used for classification of small-for-gestational-age births.
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.
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.
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.
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.
In order to elucidate whether maternal plurality affects offspring intrauterine growth, the relationship between birthweight and gestational age of twins and singletons and those of their first singleton liveborn children in Norway was studied using data from the Medical Birth Registry. The population-based sample consisted of 49,698 mother-offspring pairs (48,842 with singleton and 856 with twin-mothers). In bivariate analyses, no significant differences in mean birthweight and gestational age of offspring of twin and singleton mothers were found, although the mean birthweight and gestational age of the twin-mothers themselves were significantly lower than those of singletons (819 g and 14 days respectively). In multiple regression analysis, the expected birthweight of offspring was 230.3 g (95% CI: 193.2-267.4 g) higher when the mother was a twin than when the mother was a singleton, when controlling for non-standardised maternal birthweight. When adjusting for relative maternal birthweight (z-score), the association between maternal plurality and offspring birthweight was not statistically significant. The results suggest that being born as a twin has no substantial consequences on offspring growth in utero and show that mean differences in birthweight between twins and singletons should be standardised when both groups are included in multivariate studies.
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.
Information collected through the Medical Birth Registry of Norway on a seven-year cohort of 457,465 live births for the years 1967--73 were used to determine the factors associated with the risk of respiratory distress syndrome (RDS). A total of 1235 cases were identified and 510 of these died, resulting in an incidence rate of 2.7 and a mortality rate of 1.1 per 1000 live births. From a geographic breakdown of counties there was no association of the incidence or mortality of RDS with such environmental factors as latitude, longitude, urbanization, industrialization or level of obstetric care. There was an increase in reported incidence and mortality over time, and a slight peak during fall months. The major factors associated with the risk of RDS in Norway were birth weight, gestational age, male sex, cesarean sections and some other complications of pregnancy or delivery. When rates were adjusted for birth weight and gestational age there was no association with maternal age, parity or marital status. Such adjustments reversed the risk of RDS among multiple births to a rate lower than that for single births.
Information on personnel, equipment and care facilities at all maternity institutions has been related to the perinatal mortality among all single births in Norway, 1967--1973. There was a total of 454,358 single births during this seven year period which comprised the study data set. An obstetric score based on personnel and equipment as defined in a previous study has been used to divide the country into three groups of counties, with low, medium and high obstetric scores. Perinatal, fetal and early neonatal (less than seven days) mortality rates specific to birth weight categories in 500 gram intervals have been compared between the county groups. Significant differences were found in the mortality rates between the group of counties with low obstetric score and the two other groups. There is both a relative and absolute increased difference in mortality for births weighing 3000 grams or more compared to births less than 3000 grams. The major component in the perinatal mortality difference is due to a difference between the low and higher obstetric score county groups in the early neonatal mortality rates. Time trends indicate that the relative differences in perinatal mortality are not decreasing over the seven year period, but rather, have increased slightly. Potential differences in the populations at risk in the three county groups are discusses. An adjustment was made to eliminate the effects of some potential confounding variables, namely high parity and maternal age and illegitimacy, without basically changing the results.