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 aim of this study was to investigate whether the birthweight of Scandinavian children varies according to the social class of their parents, especially the mother. Data were taken from the Scandinavian part of an international multicentre study of fetal growth and perinatal outcome. The occupations of the pregnant woman, her spouse and her parents were registered according to the Nordic classification of occupations. This classification has been criticised for being too detailed to be suitable in epidemiological studies, and the data were recorded into the British system of five classes. The birthweight of female newborns in social class V was 301 g lower than in the other social classes (p
A study was conducted in Norway on all 454,358 single births which occurred during the 1967-73 period. The results confirm and strengthen earlier findings regarding the tendency to repeat low-birth-weight and small- or large-for-gestational age deliveries in later births. Data collected from the Medical Birth Registry included information on birth weight, length of gestation, mothers' health during pregnancy, and complications and interventions during labor and delivery. A contour level graph was prepared to illustrate the joint distribution of gestational age and birth weight. Relative risks were calculated for each type of birth. These risks were correlated with actual outcome of subsequent births. The tendency to repeat birth weight in later births was greatest for mothers of heavy infants. The tendency to repeat gestational age in subsequent births, however, was greatest for mothers with preterm infants. Delivery of prior preterm births carried a lower risk than delivery of prior low-weight births. These tendencies were unaffected by the sex of the offspring or the birth order. The pattern of repeating similar gestational age and birth weight subsequently could not be accounted for by a tendency to repeat medical complications which predispose toward such outcomes. Such environmental factors as smoking or socioeconomic status were not believed to be relevant in the study results. The study demonstrates a cumulative risk for 3rd and later pregnancies.