A new sequential procedure for surveillance of Down's syndrome

A new method is proposed for the surveillance of Down's syndrome among newborn. Despite the strong dependence of overall risk of Down's syndrome on maternal age, it has been suggested that an environmentally induced increase in risk may be additive over all maternal ages. The surveillance method introduced here is specifically designed to detect such changes. The method is based on registry data for successive periods for a given population. It is assumed that the number of Down's syndrome cases as well as the total number of births are known in all maternal age groups. Tables of average run lengths until an alarm (ARLs) are calculated for a total sample size of 14,500 in each period, the approximate number of births in a three-month period in Norway. Comparison with the Poisson cusum shows that the new surveillance method can detect moderate additive increases significantly faster. Applied retrospectively to quarterly data from the Medical Birth Registry of Norway for 1978–89, the proposed method was close to an alarm in 1985 and actually signalled a strong alarm in 1986, reflecting a previously reported increase in risk in this period. The cusum method was not so sensitive to the aberration in Down's syndrome risks in 1985 and 1986.     

Parity specific perinatal mortality. A longitudinal study based on sibships

Perinatal mortality in sibships has been examined using the Medical Birth Registry of Norway. Using linear logistic regression, parity specific perinatal mortality in the period 1967-1981 has been analysed, controlling simultaneously for maternal age, year of birth and survival of earlier births. The risk of a perinatal loss was increased by a factor of up to 6.0 following one earlier perinatal loss, and with three earlier losses the increase was 17.0. The general reduction in mortality between the different five year periods varied according to parity and maternal age. No secular reduction in risk, however, was demonstrated in sibships where the first birth died perinatally; for some subgroups of women the risk actually increased between the first and the second five year period. The effect of maternal age changed with parity, being strong in the first birth order, but of no effect either for the third or the fourth birth orders once the perinatal survival of earlier births was controlled for. This study shows the need to take heterogeneity of risk between women into account in studies of perinatal loss; the overall improvement in perinatal mortality does not apply to every woman. As care improves, perinatal losses become less and less random, demonstrated by increased risks of recurrence.     

Maternal smoking, birthweight and gestational age in sudden infant death syndrome (SIDS) babies and their surviving siblings

To evaluate the effect of maternal smoking on intrauterine growth of babies who died of sudden infant death syndrome (SIDS), birthweights of SIDS infants and their surviving siblings were compared with birthweights of infants in sibships were all infants survived the first year of life. We studied 184 349 mothers with at least two births registered in the population-based Swedish Medical Birth Registry during 1983–91. The mother being the unit of analysis, birthweight and gestational age of her infants were the repeated measures used in a repeated measures analysis of variance. Mothers whose first two infants survived at least 1 year, smoked less than mothers of SIDS infants, 25 and 41% ( P < 5 0.01). Overall, SIDS mothers did not smoke more while pregnant with the SIDS infant than while pregnant with the surviving sibling. SIDS siblings weighted, on average, 90 g less than infants in non-affected sibships. SIDS babies were even lighter, 193 g, and had 3.8 days shorter mean gestational age, compared with same birth-order babies in non-affected sibships. After adjustment for gestational age, the birthweight difference changed only slightly for SIDS siblings, while the difference for SIDS infants was reduced from 193 to 110 g. Further adjustment for smoking reduced the birthweight difference for SIDS siblings, from 74 to 50 g, and SIDS infants, from 110 to 82 g. Intrauterine growth retardation of sibships with a SIDS baby is explained only partly by maternal smoking. The even lower birthweight of the SIDS baby, resulting from shorter gestational age, cannot be explained by smoking, suggesting pregnancy factors specific to the SIDS baby and not to its siblings.     

The heavier the better? Birthweight and perinatal mortality in different ethnic groups

BACKGROUND: Mother's ethnicity is associated with her baby's birthweight and risk of perinatal mortality. Given the close relation between birthweight and perinatal mortality, we explored whether ethnic differences in birthweight explain ethnic differences in perinatal mortality. METHODS: Data on all births to mothers born in Norway (808 658), Pakistan (6854), Vietnam (3283) and North Africa (1461) from 1980 to 1995 were obtained from the Medical Birth Registry of Norway. The associations between birthweight and perinatal mortality among ethnic groups were analysed using univariate and multivariate methods. RESULTS: Mean birthweights were low for Vietnamese and Pakistani mothers (3202 g, 3244 g) and high for Norwegian and North African mothers (3530 g, 3559 g). Mean birthweights were largely unrelated to perinatal mortality, which was lowest for Vietnamese (8.2/1000, 95% CI: 5.1-11.3) and highest for Pakistanis (14.9/1000, 95% CI: 12.0-17.7). Intermediate perinatal mortality rates were found among Norwegians (9.5/1000, 95% CI: 9.3-9.7) and North Africans (9.6/1000, 95% CI: 4.6-14.6). Further comparison of weight-specific mortality rates between the two largest ethnic groups showed the low birthweight paradox, where among low-weight births, perinatal mortality was lower among Pakistani than among Norwegian babies. However, adjustment to a relative birthweight scale (units of standard deviations from population-specific mean value) revealed higher rates of weight-specific mortality among Pakistanis across the entire range of birthweights. Multivariate adjustment for relative birthweight and other factors did not change these results. CONCLUSIONS: Differences in perinatal mortality between the ethnic groups were not explained by differences in mean birthweight. Paradoxical differences in birthweight-specific mortality rates could be resolved by adjustment to a relative scale.     

The reproductive health of daughters of pregestational diabetic women: Medical Birth Registry of Norway

Maternal diabetes may have an impact upon a daughter's reproductive health through genetic influences, an altered fetal metabolic environment or both. We examined the reproductive health of daughters of diabetic women using linked generation data from the Medical Birth Registry of Norway. Among all female births between 1967 and 1982 (n = 459182), 739 had a mother with registered pregestational diabetes, a rate of 1.6 per 1000 deliveries. A total of 142904 daughters delivered at least one child by 1998. After taking into account differences in survival, we observed no differences in the percentage of childbearing and in the average number of children born by 1998 between daughters with and without a diabetic mother in age-stratified analyses. In analyses limited to singleton deliveries and stratified by mothers' and daughters' diabetic status, we found a threefold excess stillbirth delivery rate among women who had either a mother with pregestational diabetes (2.6%) or pregestational diabetes themselves (2.6%) compared with the stillbirth delivery rate observed in non-diabetic women with no maternal history of diabetes (0.8%). These findings were unaltered in multivariable analyses adjusting for daughters' maternal age and registered obstetric risk factors. Our results indicate that pregestational diabetes remains a health care challenge in Norway and that further evaluation of the reproductive health of daughters of diabetic pregnancies is warranted.     

Down's syndrome and paternal age in Norway

There is strong evidence for an effect of maternal age on the risk of Down's syndrome. An effect of paternal age has been suspected, but so far neither confirmed nor completely excluded. Large population-based data that allow detailed adjustment for maternal age are needed for a definitive analysis of the paternal age effect. We used data from the Medical Birth Registry of Norway recorded from 1967 to 1998. A total of 1738852 children were included in the analysis. A total of 10.3 per 10000 newborns had Down's syndrome. The data were fitted to logistic regression models with careful control for maternal age, birth calendar year and place of birth. When maternal age was adjusted for using categories of 5-year intervals, residual confounding still resulted in a strong effect of paternal age. However, when the shape of the effect of maternal age was well captured by the model, the estimated effect of paternal age was weak (1.11-fold increased risk per 10 years of paternal age, 95% CI of odds ratio 0.99, 1.22) and not statistically significant.     

Families with a perinatal death: is there an association between the loss and the birthweight of surviving siblings?

Our objective was to study birthweight among surviving siblings in families with and without a perinatal loss, and to evaluate whether different causes of death were associated with the results. Data were for 1967-98 from the Norwegian Medical Birth Registry. Births were organised with the mother as the observation unit through the personal identification number, providing sibship files. We analysed 550 930 sibships with at least two singletons, 208 586 sibships with at least three singletons and 45 675 sibships with at least four singleton births. We compared mean birthweight and gestational age between infants in sibships with and without a perinatal loss, total losses and the different causes of death. Surviving siblings in families with a perinatal loss had significantly lower mean birthweights than their counterparts in unaffected families, after adjusting for gestational age, interpregnancy interval, time period and marital status. An exception was found when cause of death was a birth defect, when growth retardation among surviving siblings was not found on average. We conclude that families who have lost an infant because of a birth defect do not appear to have an increased risk of adverse birth outcome associated with growth restriction.     

Infants' length at birth: an independent effect on perinatal mortality

AIM: To investigate whether variations in birth length (crown-heel-length) were associated with perinatal mortality rate independent of birth weight. MATERIAL: The study population was singleton live- and stillbirths from 16 weeks of gestation compiled in the Medical Birth Registry of Norway from 1967 to 1997, totaling 1,705,652 births. METHOD: The total population was analyzed using z-scores for length at birth, birth weight and gestational age. Variation in perinatal mortality by length at birth was studied within birth weight strata (250 g) by logistic regression. RESULTS: Perinatal mortality varied more by birth length than by birth weight or gestational age, especially for values above the population means. Within birth weight strata, the association between perinatal mortality and length was similar in all 250 g birth weight categories above 1,500 grams: mortality was lowest at birth lengths 0-2 cm below average, with mortality rates increasing exponentially in either direction. CONCLUSION: Within all birth weight strata, and adjusted for gestational age, long infants had the higher risk of perinatal death, suggesting that length at birth may be a valuable predictor when assessing the risk of perinatal mortality.     

Risk factors for maternal death in the highlands of rural northern Tanzania: a case-control study

Background  

Tanzania has one of the highest maternal mortality ratios in sub-Saharan Africa. Due to the paucity of epidemiological information on maternal deaths, and the high maternal mortality estimates found earlier in the study area, our objective was to assess determinants of maternal deaths in a rural setting in the highlands of northern Tanzania by comparing the women dying of maternal causes with women from the same population who had attended antenatal clinics in the same time period.