Sudden infant death syndrome and complications in other pregnancies

Sudden Unexpected Death in Fetal Life Through Early Childhood

In March 2015, the Eunice Kennedy Shriver National Institute of Child Health and Human Development held a workshop entitled "Sudden Unexpected Death in Fetal Life Through Early Childhood: New Opportunities." Its objective was to advance efforts to understand and ultimately prevent sudden deaths in early life, by considering their pathogenesis as a potential continuum with some commonalities in biological origins or pathways. A second objective of this meeting was to highlight current issues surrounding the classification of sudden infant death syndrome (SIDS), and the implications of variations in the use of the term "SIDS" in forensic practice, and pediatric care and research. The proceedings reflected the most current knowledge and understanding of the origins and biology of vulnerability to sudden unexpected death, and its environmental triggers. Participants were encouraged to consider the application of new technologies and "omics" approaches to accelerate research. The major advances in delineating the intrinsic vulnerabilities to sudden death in early life have come from epidemiologic, neural, cardiac, metabolic, genetic, and physiologic research, with some commonalities among cases of unexplained stillbirth, SIDS, and sudden unexplained death in childhood observed. It was emphasized that investigations of sudden unexpected death are inconsistent, varying by jurisdiction, as are the education, certification practices, and experience of death certifiers. In addition, there is no practical consensus on the use of "SIDS" as a determination in cause of death. Major clinical, forensic, and scientific areas are identified for future research.

Overall Postneonatal Mortality and Rates of SIDS

BACKGROUND

Reductions in sudden infant death syndrome (SIDS) are commonly attributed to modifications in infant sleep environments. Approaches to diagnosis in sudden infant death, death scene investigations, the prevalence of intrinsic risk factors for SIDS, and the potential influence of treatment-related factors on infant vulnerability have also changed. Understanding all contributory factors may help reduce residual SIDS rates.

METHODS

We analyzed US Mortality Multiple Causes Records for 1983 to 2012 to compare SIDS postneonatal mortality rates with a projection applying non-SIDS mortality changes, using those changes as a proxy measure for alterations in intrinsic risk. Composites of neglect-related, unknown, and circumstantial respiratory diagnoses were measured, as was a cumulative composite of unexplained infant death diagnoses. Cluster analysis with leading causes of postneonatal mortality and SIDS mortality rates for low birth weight infants were also examined.

RESULTS

SIDS and non-SIDS postneonatal mortality rates were concordant over time. Important variance was seen 1994 to 1996, coinciding with Back-to-Sleep initiation. Other variance, eliminated in the cumulative composite, appeared related to differences in diagnostic practices. Changes in SIDS rates resembled changes in mortality from congenital malformations, respiratory distress of the newborn, and diseases of the circulatory system. SIDS rates for low birth weight infants followed broader postneonatal trends.

CONCLUSIONS

SIDS mortality followed trends in overall postneonatal mortality, including effects of changes in the infant sleep environment and diagnostic classification. Preventing asphyxia risk in the sleep environment must be coupled with efforts to understand intrinsic biological pathways, some potentially associated with other categories of infant and perinatal mortality.

Maternal and perinatal risk factors for SIDS: a novel analysis utilizing pregnancy outcome data

A number of maternal and perinatal factors to increase an infant's risk of sudden infant death syndrome (SIDS) have been found in past investigations. We analysed data for potential SIDS risk factors including the presence of complications or conditions considered as detrimental to the infant's or mother's health. The data for 118 SIDS cases and 227 matched controls were obtained from a state pregnancy outcome unit. SIDS was found to be significantly more common in cases where the infant's mother was not in a relationship (i.e. divorced, separated or never married) (p = 0.005), if the infant was not the first born (p = 0.0001) and when the mother resided in a socioeconomically disadvantaged area (p = 0.03).

CONCLUSION

Overall, this SIDS cohort appears to display classical SIDS associations, and our findings are consistent with those from other regions. This novel epidemiological tool opens the way for a national Australia-wide study using pregnancy outcome data collected by the individual states and could be helpful in assessing maternal and fetal risk factors for other paediatric medical conditions.

Small size for gestational age and the risk for infant mortality in the subsequent pregnancy

PURPOSE

To examine the association between small for gestational age (SGA) in the first pregnancy and risk for infant mortality in the second pregnancy.

METHODS

This is a population-based, retrospective cohort study in which we used the Missouri maternally linked cohort dataset for 1978-2005. Analyses were restricted to women who had two singleton pregnancies during the study period. The exposure was SGA in the first pregnancy, whereas the primary outcome was infant mortality in the second pregnancy. Kaplan-Meier Estimate and Cox proportional hazard regression were conducted.

RESULTS

Infant mortality was significantly greater among mothers with previous SGA (P < .01). A persistent association of previous SGA with subsequent infant mortality was observed (adjusted hazard ratio [AHR] 1.35, 95% confidence interval [95% CI] 1.24-1.48). Race-specific data illustrated that black women with a previous SGA birth were 40% more likely to experience infant mortality (AHR 1.40, 95% CI 1.21-1.63) than their counterparts without a history of SGA, but white women with a previous SGA had an increased risk of 31% (AHR 1.31, 95% CI 1.17-1.46).

CONCLUSIONS

Women with previous SGA bear increased risks for subsequent infant mortality, which was greater among black mothers. Hence, SGA plays an important role in the black-white disparity in infant mortality. Women's previous childbearing experiences could serve as important criterion in determining appropriate interconception strategies to improve infant health and survival.

The use and reporting of multiple imputation in medical research - a review

BACKGROUND

Multiple imputation (MI) is an advanced, principled method of dealing with missing data in statistical analyses, a common problem in medical research. This paper sought to document the use of MI in general medical journals and to evaluate the information provided to readers about the application of the procedure in studies.

METHODS

Research articles using MI in analyses published in JAMA, New England Journal of Medicine, BMJ and the Lancet were identified using full text searches from the earliest date each journal offered such searches until the end of 2008. Ninety-nine articles were found. Studies were classified according to their design.

RESULTS

Multiple imputation was used in 49 RCTs and 50 other types of studies. A third of the articles (n = 33) reported no details of the procedure used. In a third of these (n = 11), it was not possible to infer the approach used from references cited or software used. The nature of the imputation model was rarely reported. MI was frequently used as a secondary analysis (n = 40) either to justify reporting a simpler approach or as a form of sensitivity analysis.

CONCLUSIONS

Whilst still relatively uncommon, the use of MI has risen substantially, particularly in trials. MI is rarely adequately reported, leading to doubt about its appropriateness in some cases. This gives rise to uncertainty about conclusions reached and poses a barrier to attempts to replicate analyses. Guidelines for the reporting of MI should be developed.

Apolipoprotein E e4 and its prevalence in early childhood death due to sudden infant death syndrome or to recognised causes

BACKGROUND

Specific genetic polymorphisms have been shown to be more common in unexplained infant death. The APOE genotype exhibits opposite effects at the extremes of age with protective effects of e4 on perinatal mortality but detrimental effects as age progresses.

OBJECTIVE

To determine whether the APOE e4 allele is associated with early childhood (1 week-2 years) unexplained death ('sudden infant death syndrome', SIDS) or with recognised causes (non-SIDS) and to compare these cohorts with published perinatal and adult data.

METHODS

DNA was extracted from spleen tissue of children dying in South East Scotland between 1990 and 2002. APOE alleles (e2, e3, e4) were determined using PCR. Comparisons of allele frequencies between groups were made.

RESULTS

There were 167 SIDS cases and 117 non-SIDS cases. Allele distributions of SIDS cases were similar to healthy newborns. Allele distributions of non-SIDS cases were more similar to adults than to healthy newborns. The percentage of children with at least one e4 allele was significantly lower in non-SIDS compared to SIDS (p = 0.016). Non-SIDS cases had a higher frequency of e3 compared to SIDS cases (p = 0.01) and to healthy newborns (0.005).

CONCLUSIONS

Children dying from identified causes have different APOE allele distributions from SIDS cases, but are similar to adults. Children dying from SIDS have an allele distribution comparable to healthy newborns. The prevalence of e4 in SIDS is not of an order to contribute significantly to the age-related decline in e4.

Customised birthweight standards accurately predict perinatal morbidity

OBJECTIVE

Fetal growth restriction is associated with adverse perinatal outcome but is often not recognised antenatally, and low birthweight centiles based on population norms are used as a proxy instead. This study compared the association between neonatal morbidity and fetal growth status at birth as determined by customised birthweight centiles and currently used centiles based on population standards.

DESIGN

Retrospective cohort study.

SETTING

Referral hospital, Barcelona, Spain.

PATIENTS

A cohort of 13 661 non-malformed singleton deliveries.

INTERVENTIONS

Both population-based and customised standards for birth weight were applied to the study cohort. Customised weight centiles were calculated by adjusting for maternal height, booking weight, parity, ethnic origin, gestational age at delivery and fetal sex.

MAIN OUTCOME MEASURES

Newborn morbidity and perinatal death.

RESULTS

The association between smallness for gestational age (SGA) and perinatal morbidity was stronger when birthweight limits were customised, and resulted in an additional 4.1% (n=565) neonates being classified as SGA. Compared with non-SGA neonates, this newly identified group had an increased risk of perinatal mortality (OR 3.2; 95% CI 1.6 to 6.2), neurological morbidity (OR 3.2; 95% CI 1.7 to 6.1) and non-neurological morbidity (OR 8; 95% CI 4.8 to 13.6).

CONCLUSION

Customised standards improve the prediction of adverse neonatal outcome. The association between SGA and adverse outcome is independent of the gestational age at delivery.

Identifying infants at risk for sudden infant death syndrome

PURPOSE OF REVIEW

This review examines recent research relevant to the underlying pathophysiology and risk factors for sudden infant death syndrome.

RECENT FINDINGS

Current research focuses on the linkage between known risk factors and vulnerability, genetic contributions, and the role of dysfunctional brainstem neurotransmission in the pathogenesis of this syndrome. While social inequalities, prematurity, maternal smoking, infant sleeping practices and sleep environment, arousal failures and environmental pollutants remain important risk factors, new evidence is emerging that certain genetic polymorphisms may contribute to vulnerability. New neuropathological studies have provided strong support for abnormal brainstem serotonergic function. Since serotonin influences a wide range of physiological systems including breathing, the cardiovascular system, temperature, and sleep-wake cycles, this finding strongly supports the hypothesis that sudden infant death syndrome is the result of dysregulation of the autonomic nervous system and provides biological plausibility for certain risk reduction strategies.

SUMMARY

Despite a putative diagnostic shift, sudden infant death syndrome remains the most common cause of death from 1 month to 1 year of age. Recent studies confirmed established risk factors and have suggested new genetic vulnerabilities. Finally, new evidence supports a key role for abnormalities in brainstem serotonin systems in the pathophysiology of this syndrome.