Accurate, unbiased malformation rates in twins must be obtained unselectively from population-based studies that include livebirths and stillbirths after a thorough ascertainment of cases. This type of study was conducted in Los Angeles County, California, where 28 twins with a neural tube defect (NTD) were identified. The prevalence in twins (1.6/1,000) was significantly higher than in singletons (1.1/1,000). The study then was expanded to include population-based data from the Medical Birth Registry of Norway which has a comparable overall NTD prevalence (1.0/1,000) and twinning rate (2%). The combined material shows a higher prevalence of anencephaly and encephalocele but not of spina bifida in twins compared to singletons. The male/female ratios in total twin and singleton cases were comparable (0.8), but varied by specific defect. Like-sex twin females appeared at highest risk for NTD as well as for fetal death. This study supports theories which associate NTDs with monozygotic twins, either through developmental disruptions that cause susceptibility to environmental agents or through a common etiology. Furthermore, it suggests that twins and singletons differ in their response to etiologic factors for the development of NTDs and that the development of each type of NTD may be related to different factors.
Given the observed variation in birth prevalence and recurrence rates of neural tube defects, it is important to obtain such data specific to a given locality for research and genetic counseling purposes. A review of hospital medical charts, the patient lists of the Medical Genetics and Myelomeningocele clinics at Alberta Children's Hospital and data from the Canadian Congenital Anomalies Surveillance System revealed the annual birth prevalence rate of neural tube defects in southern Alberta in 1970-81 to be 1.62/1000 total births. This figure suggests southern Alberta to be a low-frequency area. There was no significant variation in the annual rates of spina bifida, encephalocele or all neural tube defects combined over the study period. A significant linear decline in the frequency of births of anencephalic infants, however, was noted (p = 0.025). Information on the total reproductive history of the mothers revealed that the empiric risk of recurrence of a neural tube defect was 2.2%, and the risk to all siblings was estimated to be 2.3%. In future prevalence studies multiple sources of case ascertainment should be used, including data on pregnancies terminated because of a fetal neural tube defect.
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From: Fortuine, Robert et al. 1993. The Health of the Inuit of North America: A Bibliography from the Earliest Times through 1990. University of Alaska Anchorage. Citation number 151.
UAF - Rasmuson Library E98.A55 G86 1984 ALASKA
We describe a series of investigations that were conducted in support of the Task Force on Chemicals in the Environment and Human Reproductive Problems in New Brunswick. Geographic and temporal analyses and case-control studies, with the use of vital statistics, hospital records, the Canadian Congenital Anomalies Surveillance System and chemical databases, revealed no association between pesticides used in forestry and reproductive problems. Evidence of an association between the potential exposure to agricultural chemicals and three major anomalies combined as well as spina bifida without hydrocephalus was found. More plausible was an association between stillbirths and such exposure during the second trimester of pregnancy. This finding, along with the cyclic patterns of stillbirth in the agricultural Saint John River basin and the somewhat higher stillbirth rates in New Brunswick than in adjacent provinces or in Canada as a whole, suggests that further attention should focus on possible associations between agricultural activity and stillbirths.
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The survival for children with spina bifida has dramatically increased during the last 30 years. In Sweden today 40-50 adolescents with spina bifida are reaching adulthood each year the next 10 years. Children with spina bifida are from birth to adulthood followed by a multidisciplinary medical and paramedical team within the habilitation organisation. However, from the age of 18 this responsibility is discontinued, often with less readiness in adult medicine to meet the spina bifida adolescents and their special needs. Facing adolescence and adulthood both children and parents need a careful preparation from several points of view for the transition. It is also most important to prepare the adult medical disciplines about the special needs of this group. This process has to start early to reach successful management, including improvement in self-care.
Clustering of malformations and especially of spina bifida in Sweden was studied using the Register of Malformations and the Medical Birth Records Register. The incentive to this study was provided by the observation of a cluster of malformations, notably spina bifida, and perinatal deaths, locally thought to be related to the use of herbicides in forestry. This cluster was verified but it was shown that a high rate of spina bifida existed in the region before the introduction of herbicides in forestry. Some other clusters of spina bifida were identified and also a number of clusters of other malformations. Case-history studies were performed but revealed no lead to an explanation. Principles in the origin of the clusters and their analysis are discussed.