Secular trends in breastfeeding and parental smoking

To explore the association between smoking and breastfeeding, we obtained data from a retrospective questionnaire-based national survey comprising a random sample (n = 34799) of all mothers giving birth in Norway 1970-91. Variables studied were postpartum smoking habits for both parents, duration of breastfeeding, infant's year of birth and parental age. The response rate was 70% (n = 24438). During the study period, the maternal postpartum smoking prevalence decreased from 38% to 26%. The proportion breastfeeding at 6 months increased from 15% to 44% among smokers, and from 30% to 72% among non-smokers. In spite of a considerable increase in breastfeeding both among smokers and non-smokers, the proportion of breastfeeding, non-smoking women at 6 months was twice that of smoking women during the whole period. Furthermore, the duration of breastfeeding was shorter among young mothers and when the fathers were smoking. There was epidemiological evidence that the effect on breastfeeding of smoking might represent both biological and social mechanisms.

A case-control study of smoking and sudden infant death syndrome in the Scandinavian countries, 1992 to 1995. The Nordic Epidemiological SIDS Study

AIM

To establish whether smoking is an independent risk factor for sudden infant death syndrome (SIDS), if the effect is mainly due to prenatal or postnatal smoking, and the effect of smoking cessation.

METHODS

The analyses were based on data from the Nordic epidemiological SIDS study, a case-control study with 244 cases and 869 controls. Odds ratios were computed by conditional logistic regression analysis.

RESULTS

Smoking emerged as an independent risk factor for SIDS, and the effect was mainly mediated through maternal smoking in pregnancy (crude odds ratio 4.0 (95% confidence interval 2.9 to 5.6)). Maternal smoking showed a marked dose-response relation. There was no effect of paternal smoking if the mother did not smoke. Stopping or even reducing smoking was beneficial. SIDS cases exposed to tobacco smoke were breast fed for a shorter time than non-exposed cases, and feeding difficulties were also more common.

CONCLUSIONS

Smoking is an independent risk factor for SIDS and is mainly mediated through maternal smoking during pregnancy. Stopping smoking or smoking less may be beneficial in reducing the risk of SIDS.

The prognostic contribution of estrogen and progesterone receptor status to a modified version of the Nottingham Prognostic Index

The aim of this study was to test the prognostic contribution of estrogen (ER) and progesterone (PgR) receptor status to an index consisting of the number of positive lymph nodes, the mean nuclear area of the breast cancer cells (MNA), and tumour diameter. This index is compared with a Danish index, which includes the same factors but uses histological grade instead of MNA. The Danish index has been developed from the Nottingham Prognostic Index (NPI). In the present study of 1629 breast cancer patients the Cox proportional hazard method is used to examine the time-dependency of the index, and to test for interaction between the index and the hormone receptors. The index sorts the patients into groups with low, intermediate, and high risk of dying. Logistic regression analysis is used to report the sensitivity and specificity of the index with and without ER and PgR. Our index gave information comparable to that of the Danish group. However, the information given by our index is time-dependent, its strength being weaker after 5-year of follow-up. PgR and ER add information to high risk patients, but only in the first 5-year period. High risk patients with positive hormone receptors have a prognosis similar to intermediate risk ones. PgR increases the ability of the index to predict breast cancer deaths correctly by 5 percent in high risk patients. In conclusion, PgR and ER act differently in groups of patients with different risk levels when time-dependency is considered. This indicates biological differences in subgroups as defined by the index.

Sociodemographic risk factors for sudden infant death syndrome: associations with other risk factors. The Nordic Epidemiological SIDS Study

The aim of this study was to investigate associations between sudden infant death syndrome (SIDS) and social factors in the Nordic countries. A case-control study was conducted in Denmark, Norway and Sweden: The Nordic Epidemiological SIDS Study. Parents of 244 SIDS infants and 869 control infants matched on gender, age at death and place of birth filled in questionnaires. The dataset was analysed by conditional logistic regression. In univariate analysis, the following sociodemographic factors were associated with an increased risk of SIDS: low maternal age [odds ratio (OR) 7.8; 2.8-21.5], high birth order (OR 4.4; 2.5-7.5), single motherhood (OR 2.9; 1.7-5.0), low maternal education (OR 4.5; 2.8-7.1), low paternal education (OR 3.0; 1.9-4.7), maternal unemployment (OR 2.4; 1.8-3.4) and paternal unemployment (OR 4.0; 2.7-5.9). In a multivariate analysis where maternal smoking was also included, only paternal unemployment, young maternal age and high birth order remained significantly associated with SIDS. Housing conditions were not associated with SIDS. However, the risk of SIDS was high if the family had lived in their present home for only a few years (OR 2.3; 1.3-4.1). Sociodemographic differences remain a major concern in SIDS in a low-incidence situation and even in an affluent population with adequate health services.

The decline in the incidence of SIDS in Scandinavia and its relation to risk-intervention campaigns. Nordic Epidemiological SIDS Study

A prospective case-control study of sudden infant death syndrome (SIDS) in Norway, Denmark and Sweden between September 1, 1992 and August 31, 1995 comprised 244 cases and 869 matched controls. After the introduction of risk-intervention campaigns, the SIDS incidence decreased from 2.3/1000 live births in Norway, 1.6 in Denmark and 1.0 in Sweden to 0.6/1000 or fewer in all the Scandinavian countries in 1995. The decrease paralleled a decline in the prone sleeping position and there was an accompanying parallel fall in total postneonatal mortality in all three countries. Thus, the risk-reducing campaigns for SIDS have been successful not only in Norway and Denmark, starting from relatively high incidences, but also in Sweden, starting from a low incidence. During the study period, a gradual increase was observed for the effects of prone sleeping, smoking and bottle-feeding as risk factors for SIDS.

The spectrum of congenital anomalies of the VATER association: an international study

The spectrum of the VATER association has been debated ever since its description more than two decades ago. To assess the spectrum of congenital anomalies associated with VATER while minimizing the distortions due to small samples and referral patterns typical of clinical series, we studied infants with VATER association reported to the combined registry of infants with multiple congenital anomalies from 17 birth defects registries worldwide that are part of the International Clearinghouse for Birth Defects Monitoring Systems (ICB-DMS). Among approximately 10 million infants born from 1983 through 1991, the ICB-DMS registered 2,295 infants with 3 or more of 25 unrelated major congenital anomalies of unknown cause. Of these infants, 286 had the VATER association, defined as at least three of the five VATER anomalies (vertebral defects, anal atresia, esophageal atresia, renal defects, and radial-ray limb deficiency), when we expected 219 (P<0.001). Of these 286 infants, 51 had at least four VATER anomalies, and 8 had all five anomalies. We found that preaxial but not other limb anomalies were significantly associated with any combination of the four nonlimb VATER anomalies (P<0.001). Of the 286 infants with VATER association, 214 (74.8%) had additional defects. Genital defects, cardiovascular anomalies, and small intestinal atresias were positively associated with VATER association (P<0.001). Infants with VATER association that included both renal anomalies and anorectal atresia were significantly more likely to have genital defects. Finally, a subset of infants with VATER association also had defects described in other associations, including diaphragmatic defects, oral clefts, bladder exstrophy, omphalocele, and neural tube defects. These results offer evidence for the specificity of the VATER association, suggest the existence of distinct subsets within the association, and raise the question of a common pathway for patterns of VATER and other types of defects in at least a subset of infants with multiple congenital anomalies.

The epidemic of SIDS in Norway 1967-93: changing effects of risk factors

Time trends on the association of maternal age, birth order, and marital status with the risk of sudden infant death syndrome (SIDS) and non-SIDS deaths in Norway were analysed: 2356 postperinatal SIDS deaths and 4069 postperinatal non-SIDS deaths were ascertained during 1967-93. The SIDS incidence was 1.25 per 1000 in 1967, reached a peak of 2.69 in 1988, and fell to 1.22 in 1990 after the initiation of an intervention programme to avoid prone sleeping. In the entire period, young maternal age, high birth order, and unmarried motherhood were associated with SIDS. The adverse effects of young maternal age and high birth order increased continuously with time. From 1967-71 to 1990-93, the relative risk for maternal age < 20 years v maternal age 25-29 changed from 2.5 (95% confidence interval 2.0 to 3.2) to 7.0 (95% CI 4.2 to 11.9) (p < 0.0001), and for birth order 4+ nu birth order 1 from 3.2 (95% CI 2.5 to 4.2) to 14.4 (95% CI 8.3 to 24.9) (p < 0.0001). Effects on non-SIDS deaths were far weaker and no secular trends were observed. The strong association of young maternal age, high birth order, and marital status in SIDS, but not in non-SIDS, provides evidence that SIDS is an epidemiological entity. The increasing effects of young maternal age and high birth order, which continued after the sudden drop in the SIDS rate in 1990, suggest that further efforts to prevent SIDS should be aimed particularly at identifying causal mechanisms in high risk groups.

Mothers' birth weight and survival of their offspring: population based study

OBJECTIVE

To test the hypothesis that a baby's survival is related to the mother's birth weight.

DESIGN

Population based dataset for two generations.

SETTING

Population registry in Norway.

SUBJECTS

All birth records for women born in Norway since 1967 were linked to births during 1981-94, thereby forming 105104 mother-offspring units.

MAIN OUTCOME MEASURES

Perinatal mortality specific for weight for offspring in groups of maternal birth weight (with 500 g categories in both).

RESULTS

A mother's birth weight was strongly associated with the weight of her baby. Maternal birth weight was associated with perinatal survival of her baby only for mothers with birth weights under 2000 g. These mothers were more likely to lose a baby in the perinatal period (odds ratio 2.3, 95% confidence interval 1.4 to 3.7). Among mothers with a birth weight over 2000 g there was no overall association between mother's weight and infant survival. There was, however, a strong interaction between mother's birth weight, infant birth weight, and infant survival. Mortality among small babies was much higher for those whose mothers had been large at birth. For example, babies weighing 2500-2999 g had a threefold higher mortality if their mother's birth weight had been high (> or = 4000 g) than if the mother had been small (2500-2999 g).

CONCLUSION

Mothers who weighed less than 2000 g at birth have a higher risk of losing their own babies. For mothers who weighed > or = 2000 g their birth weight provides a benchmark for judging the growth of their offspring. Babies who are small relative to their mother's birth weight are at increased risk of mortality.

The relationship between maternal birthweight and gestational age in twins and singletons and those of their offspring in Norway

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.

Data linkage methods used in maternally-linked birth and infant death surveillance data sets from the United States (Georgia, Missouri, Utah and Washington State), Israel, Norway, Scotland and Western Australia

In this paper we describe the methods used to link birth and infant mortality and morbidity surveillance data sets into sibships using deterministic or multistage probabilistic linkage methods. We describe nine linked data sets: four in the United States (Georgia, Missouri, Utah and Washington State), and four elsewhere (Scotland, Norway, Israel and Western Australia). Norway and Israel use deterministic methods to link births and deaths into sibships. The deterministic linkage is usually dependent on the availability of national identification numbers. In both countries they assign these numbers at birth. Deterministic linkage is usually highly successful, and the major problem is the validation of linkages. In the United States, Western Australia and UK linkage is multistage and probabilistic. This approach is usually dependent on the calculation linkage weights from sociodemographic variables. The success rates of probabilistic methods are above 80%. Maternally-linked perinatal data open new vistas for epidemiological research. Recurrence of poor perinatal outcomes is more appropriately studied using longitudinally-linked data sets. In addition, the emergence of risk factors and the recurrence of risk factors can be studied.

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 < 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.

Small-for-gestational-age (SGA) infants born at term: growth and development during the first year of life

BACKGROUND

The purpose was to compare growth patterns and psychomotor development of healthy small-for-gestational-age (SGA) and non-SGA infants, and identify factors predictive of outcome at 13 months of age.

METHOD

A total of 265 SGA infants and 329 non-SGA controls were identified from a multicenter cohort of 5722 para 1 and 2 women who had been followed during pregnancy. The infants were examined at 2 days and at 13 months of age. Psychomotor development at 13 months was assessed with The Bayley Scale of Infant Development.

RESULTS

The SGA infants showed partial catch-up growth, but had still lower (mean +/- SEM, p < 0.0001) weight (9750 +/- 65 vs 10505 +/- 67 g), crown-heel length (75.9 +/- 0.2 vs 77.5 +/- 0.2 cm) and head circumference (46.9 +/- 0.1 vs 47.7 +/- 0.1 cm) than the non-SGA infants at 13 months. The SGA children scored equally well on the motor (PDI 106.8 +/- 1.0 vs 107.2 +/- 0.8) but lower on the mental scale (MDI 112.1 +/- 0.8 vs 116.5 +/- 0.7, p < 0.0001) of the Bayley Scale, and the asymmetric SGA scored lower than the symmetric SGA infants (MDI 110.2 +/- 1.3 vs 113.3 +/- 0.9, p = 0.05). In a multivariate regression analysis the parents' growth parameters had the greatest effect on growth measures at 13 months while education and maternal smoking had no significant effect. SGA vs non-SGA status had the greatest effect on growth velocities during infancy. For mental development only SGA vs non-SGA status and the mothers' education made significant contributions, but only accounted for 6% of the variance.

CONCLUSION

The negative impact of intrauterine factors on growth are partly abolished by catch-up growth during infancy, and growth parameters at one year of age are mostly determined by genetic factors even in SGA infants. Decreased intrauterine growth may possibly have a negative effect on brain growth and mental developmental potential.

Genotype, viral load and age as independent predictors of treatment outcome of interferon-alpha 2a treatment in patients with chronic hepatitis C. Construct group

Patients with chronic hepatitis C respond differently when treated with interferon. We randomized 116 patients with chronic hepatitis C in order to compare two dosage regimens of recombinant interferon alpha 2a:3 MIU x 3 per week for 6 months (arm A) or 6 MIU x 3 per week for 3 months and then 3 MIU x 3 per week for 3 months (arm B). There were no significant differences concerning outcome between the two dose regimens: sustained clearance of HCV viremia 6 months after the end of treatment was obtained in 12/59 (20%) in group A compared with 18/57 (32%) in group B (p = 0.24). In patients with genotype 1a, 4/31 (13%), in genotype 1b, none of 9 (0%), 9/15 (60%) in genotype 2, and 17/58 (29%) in genotype 3, showed sustained clearance of HCV viremia 6 months after the end of treatment (p = 0.002). In a stepwise logistic regression analysis, only pretreatment viral load (p = 0.0001), genotype (p = 0.001) and age (p = 0.04) were identified as independent predictors of sustained clearance of HCV viremia. Liver histology as assessed by Knodell index was significantly improved in patients with sustained HCV RNA response 6 months after the end of treatment (5.2 +/- 2.2 vs 2.6 +/- 2.2, p < 0.001), but not in responders with relapse or in non-responders. In conclusion, stepwise logistic regression analysis showed that viral load, HCV genotype and age were the only independent predictors for sustained HCV RNA response.

Prognostic role of oestrogen and progesterone receptors in patients with breast cancer: relation to age and lymph node status

AIMS

To consider the prognostic role of oestrogen receptor and progesterone receptor status in relation to the age at surgery, length of follow up and lymph node status.

METHODS

The study population comprised 977 patients with histologically confirmed breast carcinoma, with a median follow up of nine years. The actuarial life table method was used to test for survival differences. The Cox proportional hazard model was used to test for interaction effects between each hormone receptor and age, lymph node status and length of follow up. As the analysis involved multiple subgroups, significance was set at the 1% level (p < 0.01).

RESULTS

When the patients were subdivided into groups according to lymph node status and age, progesterone and oestrogen receptor status predicted prognosis in middle aged (46-60 years) patients with lymph node positive breast cancer. Their prognostic effect in this subgroup, however, was restricted to the first five years after surgery. Progesterone receptor status was the strongest predictor of outcome.

CONCLUSION

The prognostic power of oestrogen and progesterone receptor status varies depending on age, lymph node status and length of follow up after surgery.

Statistical evidence for shared transient causes of anatomically distinct birth defects

Certain pairs of anatomically distinct birth defects co-occur in the same baby more often than predicted under independence. Such an excess might reflects either the fact that some subpopulations of parents have inherently increased risk for both, or that certain pregnancies are at increased risk for both, even within the same couple, perhaps, due to transient exposures specific to the pregnancy. We focus on the latter possibility in the context of a large birth registry and two relatively common types of defects, by testing the null hypothesis that within sibships the two defects occur independently. Focusing on sibships where both defects occurred, we propose a test based on the total number of 'co-incidences', sibships where both occurred in the same baby. Such a test can be carried out either with or without allowance for possible dependence of risk on birth order. Applying this to club foot and sex organ defects among sibships from the Medical Birth Registry of Norway, we find strong evidence for excess within-family co-incidence, suggesting that there are shared, time-varying (hence perhaps modifiable) causal components in their aetiology.

Population-based recurrence risk of sudden infant death syndrome compared with other infant and fetal deaths

To investigate the recurrence of sudden infant death syndrome (SIDS) among siblings, the authors analyzed data for all 352,475 mothers whose first and second single births were reported to the Medical Birth Registry of Norway during 1967-1988. Recurrence of stillbirths from the 16th week of gestation onward and infant deaths other than SIDS were also studied. Relative risk of recurrence for SIDS was 5.8 (95% confidence interval (CI) 2.1-13.2); for asphyxia- and immaturity-related infant deaths, 12.5 (9.2-17.4); for congenital malformations, 7.2 (4.7-11.0); and for other causes of infant death, 8.0 (2.0-22.1). Deaths due to infections did not recur. Similar categories of infant deaths had higher overall relative risk, 9.1, compared with 1.6 for dissimilar categories. Previous early stillbirth (16-27 weeks) had a high recurrence (relative risk (RR) = 21.8, 95% CI 17.5-26.9), while late stillbirth (> or = 28 weeks) had lower recurrence (RR = 4.6, 95% CI 3.7-5.8). Previous SIDS was associated with an increased risk of all other types of loss. In contrast, previous late stillbirth and previous asphyxia- and immaturity-related infant deaths were associated with a reduced risk of subsequent SIDS (RR = 0.31, 95% CI 0.08-0.84, and RR = 0.23, 95% CI 0.01-1.13, respectively). In conclusion, as with other infant and fetal deaths, SIDS deaths showed strong sibship aggregation consistent with a genetic susceptibility in subsets of SIDS that may interact with environmental factors. The authors also suggest common pregnancy-specific risk factors for late stillbirths, asphyxia- and immaturity-related infant deaths, and SIDS.

Flow cytometric measurement of DNA S-phase in human bone marrow cells: correcting for peripheral blood contamination

The relationship between bone marrow (BM) cells with S-phase DNA content and the amount of peripheral blood contamination estimated as percentage lymphocytes+monocytes (L+MO) present in BM samples has been investigated in a total of 136 BM aspirates and biopsy expellates from 35 hematologically healthy individuals. A significant negative correlation was demonstrated between total, erythroid and myeloid BM cells in S-phase and the percentage of L+MO in the aspirates (r=0.84, 0.57 and 0.49, respectively; p<0.0001). Based on the equation of the slope of the regression line, a correction formula adjusting the measured value of BM cells in S-phase to varying amounts of L+MO percentage has been worked out for the total and erythroid BM cells. In contrast, highly proliferating myelomonocytic cells and CD34+ cells did not show any significant correlation between cells in S-phase and percentage L+MO, indicating that peripheral blood contamination of BM aspirates estimates the degree of peripheral blood contamination, as well as make possible a correct estimation of the DNA synthesis of several BM populations. The method is especially applicable when frequent BM sampling is required.

Fetal growth retardation in sudden infant death syndrome (SIDS) babies and their siblings

To evaluate the intrauterine growth potential of infants that die from sudden infant death syndrome (SIDS), the authors compared SIDS infants with their surviving siblings. The SIDS sibships themselves were also compared with sibships where all infants survived. Data from the population-based Medical Birth Registry of Norway, with 1.3 million births during 1967-1988, were used. From the birth cohorts, 1,984 SIDS cases were identified. All births were linked into sibships. The mean birth weight and gestational age were calculated across sibships of different sizes for first to fourth birth order. In a further analysis, birth weights were standardized to adjust for gestational age. Mothers of SIDS infants give birth to smaller babies in general. SIDS infants weighed, on average, 85 g less at birth than their siblings and 164 g less compared with babies in nonaffected sibships. When birth weights were standardized for gestational age, most of the weight difference between SIDS infants and siblings was due to a shorter gestational age of SIDS infants, while the difference between surviving siblings of SIDS infants and births from nonaffected sibships remained. All births in sibships with a SIDS infant were intrauterine growth retarded. This may reflect factors that contribute to SIDS risk (such as maternal smoking). The factors that contribute to shorter gestational age and further slowing of growth in the SIDS infants may specifically influence the SIDS infant and not its siblings.

Sleeping position and sudden infant death syndrome in Norway 1967-91

OBJECTIVE

To investigate, in a population based national study, the association between sleeping position of infants and the occurrence of sudden infant death syndrome (SIDS).

DESIGN

A retrospective survey and registry based ecological study. A questionnaire based surveillance of sleeping position was obtained in a random sample (n = 34,799) and surveillance of SIDS was based on all infants born in Norway 1967-91, surviving the perinatal period. Variables studied from the questionnaire were usual sleeping position (placed), breast feeding at 3 months, and maternal smoking in pregnancy, and from the Medical Birth Registry maternal age, birth order, and birth weight.

RESULTS

Proportion of infants sleeping prone increased from 1970 (7.4%) to 1989 (49.1%) and dropped in 1990 (26.8%) and 1991 (28.3%). Occurrence of SIDS increased from 1970 (1.1/1000) to 1989 (2.0) before dropping in 1990 and 1991 (1.1). IMPLICATION AND RELEVANCE OF RESULTS: A cause effect relationship between prone sleeping and SIDS as suggested in previous studies is supported by the present; and so far only, national study of infants' sleeping position.

Longitudinal study of cytomegalovirus antibodies in individuals infected with the human immunodeficiency virus

Cytomegalovirus (CMV) antibody profiles were studied in 25 HIV-infected patients over periods of up to 56 months. Specific antibodies against CMV antigen components were monitored by complement-fixation (CF) test, EIA, Western blot and a neutralization assay. Three subjects remained CMV seronegative throughout the study. Marked fluctuations were observed in anti-CMV antibodies assayed by the CF test as compared to a control group. Fluctuations on immunoblots of purified virion antigens were also observed in the HIV-infected patients; neutralizing antibodies and anti-CMV nucleocapsid antibodies showed less variability. Seven of 22 individuals exhibited an increase in CF-test titre of up to 64-fold without clinically apparent CMV disease. On Western-blot testing of IgG reactivity with disrupted virions, ten individuals exhibited increasing reactivity to pp65, and only three of these also showed a titre rise in the CF test. In contrast, 7 of 22 showed low reactivity to the pp28 antigen. The homosexual patient group exhibited the highest levels of anti-CMV antibody. In conclusion, many asymptomatic HIV-infected subjects showed fluctuations at different levels of their antibody response to CMV, thought to be indicative of CMV reactivation/reinfection. Western-blot findings indicated that some CMV antibodies increased in level while others were lost.

Birth weight and perinatal mortality. A comparison of the United States and Norway

OBJECTIVE

To compare perinatal mortality in the United States and Norway, using a new analytic approach based on relative birth weight.

DESIGN

Comparison of linked birth and perinatal death records for US and Norwegian births from 1986 through 1987, the most recently available 2-year period.

SETTING

Norway and the United States.

PARTICIPANTS

A total of 7,445,914 US births and 105,084 Norwegian births.

INTERVENTIONS

None.

MAIN OUTCOME MEASURE

Perinatal weight-specific mortality after adjustment for each country's own mean birth weight.

RESULTS

The higher rate of perinatal death in the United States compared with Norway is due to an excess of preterm deliveries in the United States. Low-weight, preterm births comprise 2.9% of US births compared with 2.1% of Norwegian births. If the United States could eliminate this slight excess of preterm delivery, perinatal mortality in the United States would decrease to the level in Norway. Unexpectedly, the survival of newborns at any given birth weight is virtually the same in the United States and Norway when newborns' birth weights are considered relative to their own nation's mean weight.

CONCLUSIONS

Low rates of perinatal mortality in the Scandinavian countries have usually been attributed to the heavier weights of their newborns. Higher mortality among US infants is in fact due entirely to a small excess of preterm deliveries. The lighter weights of US newborns at term appear not to affect perinatal survival. Furthermore, the apparent survival advantage of low-weight US newborns (used by policymakers as evidence of superior US intensive neonatal care) may be at least partly an artifact. When weight-specific mortality rates are adjusted to relative birth weight, low-weight newborns have the same survival in Norway as in the United States. The prevention of excess mortality among US infants depends on the prevention of preterm births, not on changes in mean birth weight.

Harsh social conditions and perinatal survival: an age-period-cohort analysis of the World War II occupation of Norway

OBJECTIVES

The hypothesis was tested that unfavorable social conditions are associated with poor perinatal survival through direct effects on pregnancy or, more indirectly, through effects on mothers born under such conditions. The occupation of Norway by Nazi Germany was used as a period of social hardship.

METHODS

Data from Norwegian vital statistics and the Medical Birth Registry were used to describe perinatal mortality during World War II and also a generation later, among babies born to mothers who had themselves been born during the war. Logistic regression was used to identify a possible cohort effect among mothers born in 1940 through 1944 compared with mothers born before or after that period.

RESULTS

Harsh conditions in Norway during the occupation increased childhood mortality. However, perinatal mortality declined during that period. Likewise, no adverse effect was seen on the survival of babies born to mothers who had themselves been born during the war (odds ratio = 1.00; 95% confidence interval = 0.96, 1.04).

CONCLUSIONS

We find no evidence that wartime conditions in Norway impaired perinatal survival, either directly or through an effect on women born during the war. These data underscore how little is known about the ways that social conditions influence perinatal mortality.

A population-based study of the risk of recurrence of birth defects

BACKGROUND

Certain birth defects are known to recur in families, but most estimates of the risk of recurrence have come from clinic-based studies. In this study we estimated the risk of recurrent birth defects using a population-based registry.

METHODS

The study was based on the records of the first and second infants delivered by 371,933 women from 1967 through 1989. The records are maintained by the Medical Birth Registry of Norway. For the 9192 women whose first infant had a birth defect, we determined the relative risk of similar and dissimilar defects in the second infant. The reference population was women whose first infant had no defect.

RESULTS

Among first infants, 2.5 percent had a birth defect. The mothers of affected first infants were 2.4 times as likely as other women to have second infants with any registered defect. This increased risk was due primarily to an increased (7.6 times higher) risk of the same defect in the second infant as in the first (95 percent confidence interval, 6.5 to 8.8) and secondarily to a slightly increased (1.5 times higher) risk of a different defect in the second infant (95 percent confidence interval, 1.3 to 1.7). Among the women who lived in the same municipality during both pregnancies, the relative risk of having a second infant with the same defect was 11.6, as compared with 5.1 among the women who moved to another municipality after the birth of their first infant (P < 0.001).

CONCLUSIONS

Among women whose first infant has a birth defect, the risk of the same defect in the second infant is substantially increased and the risk of a different defect in the second infant is slightly increased. Environment plays a strong part in repeated defects.

Lymph node-negative breast cancer: the prognostic role and time dependency of age, tumor diameter and mean nuclear area

This study of 786 node-negative breast cancer patients demonstrates that the prognostic effect of age at operation, tumor diameter and mean nuclear area (MNA) changed over time. Identifying patients at higher risk of dying after 5 years may be of clinical importance. These are patients who may have had a low metastatic tumor burden at the time of operation and in whom cytostatic adjuvant treatment could be of value. When estimating 10-year survival, a significant loss of strength was found for age. A near significant loss of effect was also found for MNA, while tumor diameter was the variable best maintaining prognostic power during the observation period. Due to the loss of strength for MNA and age when estimating 10-year survival, the observation period was divided into two periods. When estimating 5-year survival, MNA was the strongest variable, while tumor diameter and age gave additional significant information. When estimating the next 5 years, excluding patients who died before 5 years, only tumor diameter gave significant prognostic information (573 cases). This again stresses the importance of tumor diameter in assessing prognosis in node-negative patients.

Secular trends of sudden infant death syndrome in Norway 1967-1988: application of a method of case identification to Norwegian registry data

In Norway, towards the end of the 1980s, sudden infant death syndrome (SIDS) was the most frequent cause of infant death. Both SIDS and the total post-perinatal mortality rates had increased. This paper presents a procedure for identifying SIDS from death certificates. Supplemented with additional information, a database was established to evaluate secular trends of SIDS and for further analytical research. The Medical Birth Registry of Norway comprises 1.3 million births from 1967 to 1988. Of these, 5447 infants died in the post-perinatal period. The cause of death was reviewed by an expert panel and 1984 cases of SIDS were retrieved. Low maternal age, higher birth order, male gender, and lower birth-weight were confirmed as risk factors for SIDS. In 1988, the rate for SIDS and for total post-perinatal deaths reached 2.69 and 5.02 per 1000 infants at risk. The incidence of SIDS increased 2.2 times from the period 1967-1971 to the period 1987-1988. Adjusted for maternal age, birth order, and birthweight, the odds ratio was 3.1. The increase is due to factors not yet accounted for. Adjusted mortality rates for the other post-perinatal deaths were not different from the crude rates.