Births In Iceland Research Articles

Perinatal outcomes of preterm births occuring to native-born and migrant mothers in Iceland

The aim of this study was to assess the incidence and perinatal outcomes of preterm births in Iceland during 1997-2018 and compare outcomes of Icelandic and migrant mothers. The population in this historical population-based cohort study was all preterm (p<37 weeks gestation) live-born singletons born in Iceland from January 1, 1997 to December 31, 2018 and their mothers; a total of 3837 births. Data was obtained from the Icelandic Medical Birth Registry. The group of migrant women was defined as women with other citizenship than Icelandic. Migrant women were divided into three groups based on their country of citizenship Human Development Index (HDI). Both descriptive and analytical statistics were used in data processing. The incidence of preterm births in Iceland increased during the study period (3,9% 1998-2001 vs. 4,5% 2012-2018, p<005) and was significantly higher among migrant mothers, especially from countries with the lowest HDI (OR 1,49 (CI 1,21-1,81) p<,001). Infants of mothers from countries with the lowest HDI had a significantly lower prevalence of respiratory distress syndrome compared with infants of Icelandic mothers (4,5% vs. 11,4%, p=0,035) meanwhile infants of mothers from countries with a medium high HDI were more often small for gestational age compared with infants of Icelandic mothers (11,4% vs. 6,9%, p=0,021). Preterm births have become more common in Iceland and the incidence is significantly higher among migrant mothers, however the outcomes of preterm infants are generally good and mostly comparable between Icelandic and migrant mothers.

Postpartum hemorrhage in singleton births in Iceland 2013 - 2018, incidence proportion and risk factors

Many countries have reported an increased incidence proportion of postpartum hemorrhage (PPH). The proportion might also have increased at the National University Hospital of Iceland, based on the registration of the ICD-10 code O72. This study aimed to assess the incidence proportion and risk factors for ≥1000 ml PPH in singleton births in Iceland 2013-2018. This population-based cohort study included data from the Icelandic Birth register on 21.110 singleton births in 2013-2018. Incidence proportion of PPH was assessed based on three definitions: PPH >500 ml, PPH ≥1000 ml, and O72. Binomial regression was used to assess both the change in the proportion of ≥1000 ml PPH over time, stratified by maternal BMI, and risk factors for ≥1000 ml PPH. There was an inconsistency in the proportion of PPH when defined by blood loss >500 ml and O72. In obese women, PPH ≥1000 ml was more than twice as likely in those delivering in 2018 compared with 2013 (OR 2.23; CI 1.35-3.81). The strongest risk factors were emergency cesarean (OR 2.68; CI 2.22-3.22) and instrumental delivery (OR 2.18; CI 1.80-2.64), but macrosomia, primiparity and BMI ≥30 were also independent risk factors. The incidence proportion of ≥1000 ml PPH has increased among obese women. The detrimental health effects of obesity and the increased prevalence of interventions among these women could explain these results. It is necessary to use registered blood loss in milliliters in the Icelandic Birth Register because of the under-registration of the diagnostic code O72.

Fetal genome predicted birth weight and polycystic ovary syndrome in later life: a Mendelian randomization study.

Associations between lower birth weight and higher polycystic ovary syndrome (PCOS) risk have been reported in previous observational studies, however, the causal relationship is still unknown. Based on decomposed fetal and maternal genetic effects on birth weight (n = 406,063), we conducted a two-sample Mendelian randomization (MR) analysis to assess potential causal relationships between fetal genome predicted birth weight and PCOS risk using a large-scale genome-wide association study (GWAS) including 4,138 PCOS cases and 20,129 controls. To further eliminate the maternally transmitted or non-transmitted effects on fetal growth, we performed a secondary MR analysis by utilizing genetic instruments after excluding maternally transmitted or non-transmitted variants, which were identified in another birth weight GWAS (n = 63,365 parent-offspring trios from Icelandic birth register). Linkage disequilibrium score regression (LDSR) analysis was conducted to estimate the genetic correlation. We found little evidence to support a causal effect of fetal genome determined birth weight on the risk of developing PCOS (primary MR analysis, OR: 0.86, 95% CI: 0.52 to 1.43; secondary MR analysis, OR: 0.86, 95% CI: 0.54 to 1.39). In addition, a marginally significant genetic correlation (rg = -0.14, se = 0.07) between birth weight and PCOS was revealed via LDSR analysis. Our findings indicated that observed associations between birth weight and future PCOS risk are more likely to be attributable to genetic pleiotropy driven by the fetal genome rather than a causal mechanism.

Contributing indications to intrapartum and prelabor cesarean births in Iceland 1997‐2015

AbstractBackgroundMore research is needed on the relative contributions of different indications for cesarean birth and how they vary with maternal age and across time. We aimed to assess how the relative contribution of various indications varied with age and by time period in a study of intrapartum and prelabor singleton, term cesarean births (CB) in Iceland.MethodsThe study was restricted to all singleton, term cesarean births in Iceland between 1997 and 2015 identified from the Icelandic Medical Birth Registry (n = 10 856). The contribution of indications was calculated according to maternal age‐ and birth‐year groups for primiparas and multiparas. Logistic regression was used to estimate odds ratios and 95% confidence intervals.ResultsFor intrapartum cesarean births, the relative contribution of fetal distress (AOR = 1.35 [95% CI = 1.12‐1.63]) and failed induction (1.53 [1.15‐2.00]) increased with increasing maternal age, whereas dystocia decreased (0.70 [0.58‐0.83]). For prelabor cesarean births, the contribution of malpresentation (0.83 [0.76‐0.91]) and maternal‐fetal‐obstetric indications (0.59 [0.47‐0.74]) decreased with both birth year and maternal age, whereas the contribution of fear of childbirth (1.80 [1.27‐2.54]) and adverse obstetric history (1.24 [1.12‐1.37]) increased. Previous CB as an indication for cesarean increased until the 2007‐2011 time period, after which it decreased.ConclusionsFor intrapartum cesarean births, the relative contribution of fetal distress and failed induction increased with maternal age, whereas dystocia decreased. For prelabor cesarean births, the relative contribution of more objective indications decreased, whereas more subjective indications increased with time and with increasing maternal age.

Growing importance of genetics

Fetal Biology An infant’s birth weight is associated with a variety of health outcomes all the way into adulthood. Birth weight is influenced by both fetal and maternal factors, as well as by environmental and genetic regulation. To elucidate the relative contributions of genetic factors from mother and child, Juliusdottir et al. performed genome-wide association studies on hundreds of thousands of mothers and newborns from the Icelandic birth register and other databases. Most of the genes that affected growth were part of the fetal genome, but the authors also identified some parental alleles that had specific effects, as well as pathways influenced by these genes, such as glycemic control and cardiovascular function. Nat. Genet. 53 , 1135 (2021).

Trends in cesarean birth rates in Iceland over a 19-year period.

Cesarean birth (CB) rates have increased in high-resource countries during the past two decades, yet it is not known whether CB rates have changed according to maternal age and/or gestational age. All singleton live births in Iceland between 1997 and 2015 were identified from the Icelandic Medical Birth Registry (80130). Rates of cesarean births (intrapartum and prelabor) were calculated overall and separately for maternal age groups and gestational age groups and by parity. Logit binomial regression was used to calculate odds ratios (ORs) and confidence intervals (CIs) for annual change in cesarean birth rates adjusted for maternal characteristics and clinical indication groups. The overall CB rate was 15.7% in 1997 and 15.8% in 2015; the CB rate did not change significantly during the study period. The overall CB rate for early-term deliveries (37-38weeks) decreased for multiparas (annual aOR=0.99 [95% CI=0.98-0.99]), and the preterm (<37weeks) prelabor cesarean rate increased significantly (1.11 [1.09-1.14]) for both primiparas and multiparas. For multiparas only, the intrapartum CB rate decreased (0.97 [0.97-0.98]), whereas the prelabor CB rate increased, predominantly for women aged over 35years (1.03 [1.02-1.04]). Adjustment for clinical indication groups did not change these results. Findings indicate a rise in prelabor cesarean for preterm births and women aged over 35years (multiparas only). As adjustment for clinical indications did not affect these results, changes in obstetric practice are more likely to have affected these rate changes rather than changes in clinical indications.

Pre- and Postnatal Diagnosis of Congenital Central Nervous System Anomalies in Iceland in 1992-2016

The incidence of congenital anomalies of the central nervous system (CNS) in Iceland during 1992-2016 was examined along with timing of diagnosis, maternal residence, known risk factors and perinatal outcomes. This was a retrospective study of all fe-tuses and newborns diagnosed with a CNS anomaly during the study period and their mothers. Information was obtained from the Icelandic Birth Registry and from maternal and neonatal medical records. Descriptive and inferential statistics were used in data analyzing. Annually, 3-12 cases of congenital CNS anomalies were diagnosed. Five year period incidence ranged from 1.4-2.4/1000 newborns, highest in 2012-2016. Over 89% were diagnosed -prenatally, of those 80% were terminated. The average gestational age at diagnosis of anencephaly was 19,3 weeks 1992-1996 vs. 11.6 weeks 2012-2016 (p=0,006). Urban area prenatal diagnosis was higher (94%) than rural (80%) (p=0.006). Known risk factors among mothers were uncommon, except for maternal obesity during the period 2012-2016 (23%). Of 57 live born children with CNS anomalies 37 (65%) were alive at the time of the study. The incidence of congenital anomalies of the CNS is stable and maternal risk factors are infrequent. Around 90% were diagnosed prenatally. Fetal anencephaly was diagnosed earlier at the end of the study period, after the introduction of a 11-14 week ultrasound scan in 2003, along with increased training among -healthcare professionals and improved ultrasound equipment. Higher prenatal detection rate in urban areas compared with rural may be explained by fewer ultrasound examinations being performed in less populated health districts, staff consequently receiving less training and experience and also with less advanced equipment.

Preterm births in Iceland 1997-2016: Preterm birth rates by gestational age groups and type of preterm birth.

The frequency of preterm births has been increasing globally, mainly due to a rise in iatrogenic late preterm births. The aim of this study was to assess the prevalence of preterm births in Iceland during 1997-2016 by type of preterm birth. This study included all live births in Iceland during 1997-2016 identified from the Icelandic Medical Birth Registry. Risk of preterm birth by time period was assessed with Poisson regression models adjusted for demographic variables and indications for iatrogenic births. The study population included 87076 infants, of which 4986 (5.7%) were preterm. The preterm birth rate increased from 5.3% to 6.1% (adjusted rate ratio [ARR]=1.16, confidence interval [CI]=1.07-1.26) between 1997-2001 and 2012-2016 overall. The increase was only evident in multiples (ARR 1.41, 95% CI 1.21-1.65), not singletons (1.07, 0.97-1.19). The rate of late preterm births (34-36weeks) increased significantly (1.24, 1.14-1.40), and the rate of iatrogenic preterm births more than doubled during this period even after adjustment for identified medical indications (2.40, 2.00-2.88). The rate of spontaneous preterm births decreased during the study period (0.63, 0.55-0.73), and the rate of PPROM increased (1.31, 1.09-1.57). The most common contributing indications for iatrogenic births were fetal distress (26.2%), hypertensive disorders (18.2%), and severe preeclampsia (16.9%). Preterm birth rates increased in multiples in Iceland between 1997 and 2016, and late and iatrogenic preterm births increased overall. The increase in iatrogenic preterm births remained significant after adjusting for medical indications, suggesting that other factors might be affecting the rise.

The Robson 10‐group classification in Iceland: Obstetric interventions and outcomes

Rising cesarean rates call for studies on which subgroups of women contribute to the rising rates, both in countries with high and low rates. This study investigated the cesarean rates and contributing groups in Iceland using the Robson 10-group classification system. This study included all births in Iceland from 1997 to 2015, identified from the Icelandic Medical Birth Registry (81839). The Robson distribution, cesarean rate, and contribution of each Robson group were analyzed for each year, and the distribution of other outcomes was calculated for each Robson group. The overall cesarean rate in the population was 16.4%. Robson groups 1 (28.7%) and 3 (38.0%) (spontaneous term births) were the largest groups, and groups 2b (0.4%) and 4b (0.7%) (prelabor cesareans) were small. The cesarean rate in group 5 (prior cesarean) was 55.5%. Group 5 was the largest contributing group to the overall cesarean rate (31.2%), followed by groups 1 (17.1%) and 2a (11.0%). The size of groups 2a (RR1.04 [95% CI1.01-1.08]) and 4a (RR1.04 [95% CI1.01-1.07]) (induced labors) increased over time, whereas their cesarean rates were stable (group 2a: P=0.08) or decreased (group 4a: RR0.95 [95% CI0.91-0.98]). In comparison with countries with high cesarean rates, the prelabor cesarean groups (singleton term pregnancies) in Iceland were small, and in women with a previous cesarean, the cesarean rate was low. The size of the labor induction group increased, yet the cesarean rate in this group did not increase.

Effects of an intervention program for reducing severe perineal trauma during the second stage of labor.

Obstetric anal sphincter injuries lead frequently to short- and long-term consequences for the mother, including perineal pain, genital prolapse, and sexual problems. The aim of the study was to evaluate whether the implementation of an intervention program in the second stage of labor involving altered perineal support techniques reduced severe perineal trauma. All women reaching the second stage of labor and giving birth vaginally to singleton babies at Landspítali University Hospital (comprising 76% of births in Iceland in 2013) were enrolled in a cohort study. Data were recorded retrospectively for 2008-2010 and prospectively in 2012-2014, for a total of 16 336 births. During 2011, an intervention program was implemented, involving all midwives and obstetricians working in the labor wards. Two professionals assessed and agreed on classification of every perineal tear. The prevalence of obstetric anal sphincter injuries decreased from 5.9% to 3.7% after the implementation (P<0.001). Third-degree tears decreased by 40%, and fourth-degree tears decreased by 56% (P<0.001). The prevalence of first-degree tears increased from 25.8% to 33.1%, whereas second-degree tears decreased from 44.7% to 36.6% between the before and after study periods. Severe perineal trauma was linked to birthweight, and this did not change despite the new intervention. Active intervention to reduce perineal trauma was associated with an overall significant decrease in obstetric anal sphincter injuries. Good perineal visualization, manual perineal support, and controlled delivery of the fetal head were essential components for reducing perineal trauma.

Perinatal mortality in Iceland 1988-2017

Introduction Perinatal mortality refers to stillbirth and neonatal death during the first week of life. Recently perinatal mortality rate in Iceland has been among the lowest in the world. The aim of the study was to evaluate how perinatal mortality rate and its causes have changed in Iceland during the last 30 years, particularly to see if it is possible to lower the perinatal mortality rate even more. Cases and methods The study was retrospective and included all infants that were stillborn or died during the first week of life in 1988-2017. Information was obtained from the Icelandic Medical Birth Registry, the annual reports on births in Iceland. A classification focusing on identifying groups of perinatal death that are potentially avoidable was used. An annual percent change was calculated with Poisson regression. Results The perinatal mortality rate declined on average by 3,3% per year in the period based on ≥28+0 weeks gestation. The number of infants that died because of congenital anomalies decreased on average by 4,8% per year. The number of growth restricted stillborn singletons after ≥28+0 weeks of gestation decreased on average by 3,1% per year. The number of non growth restricted stillborn singletons after ≥28+0 weeks of gestation did not decrease significantly. Conclusion Perinatal mortality rate has declined substantially in Iceland during 30 years. Deaths because of congenital anomalies have decreased considerably due to improvement in prenatal diagnosis. Stillbirths associated with growth restriction have decreased but stillbirths that are not associated with growth restriction have not. Thus it is important to emphasize that women seek medical attention when they experience decreased fetal movements.

Seasonality of sex ratio at births in Iceland and effects of the 2010 Eyjafjallajökull volcanic eruption.

Seasonality of sex ratio at births in Iceland and effects of the 2010 Eyjafjallajökull volcanic eruption.

Identification of Common Genetic Variants Influencing Spontaneous Dizygotic Twinning and Female Fertility

Spontaneous dizygotic (DZ) twinning occurs in 1%-4% of women, with familial clustering and unknown physiological pathways and genetic origin. DZ twinning might index increased fertility and has distinct health implications for mother and child. We performed a GWAS in 1,980 mothers of spontaneous DZ twins and 12,953 control subjects. Findings were replicated in a large Icelandic cohort and tested for association across a broad range of fertility traits in women. Two SNPs were identified (rs11031006 near FSHB, p = 1.54× 10(-9), and rs17293443 in SMAD3, p = 1.57× 10(-8)) and replicated (p = 3× 10(-3) and p = 1.44× 10(-4), respectively). Based on ∼90,000 births in Iceland, the risk of a mother delivering twins increased by 18% for each copy of allele rs11031006-G and 9% for rs17293443-C. Ahigher polygenic risk score (PRS) for DZ twinning, calculated based on the results of the DZ twinning GWAS, was significantly associated with DZ twinning in Iceland (p = 0.001). A higher PRS was also associated with having children (p = 0.01), greater lifetime parity (p = 0.03), and earlier age at first child (p = 0.02). Allele rs11031006-G was associated with higher serum FSH levels, earlier age at menarche, earlier age at first child, higher lifetime parity, lower PCOS risk, and earlier age at menopause. Conversely, rs17293443-C was associated with later age at last child. We identified robust genetic risk variants for DZ twinning: one near FSHB and a second within SMAD3, the product of which plays an important role in gonadal responsiveness to FSH. These loci contribute to crucial aspects of reproductive capacity and health.

Deconstructing the smoking-preeclampsia paradox through a counterfactual framework.

Although smoking during pregnancy may lead to many adverse outcomes, numerous studies have reported a paradoxical inverse association between maternal cigarette smoking during pregnancy and preeclampsia. Using a counterfactual framework we aimed to explore the structure of this paradox as being a consequence of selection bias. Using a case-control study nested in the Icelandic Birth Registry (1309 women), we show how this selection bias can be explored and corrected for. Cases were defined as any case of pregnancy induced hypertension or preeclampsia occurring after 20weeks' gestation and controls as normotensive mothers who gave birth in the same year. First, we used directed acyclic graphs to illustrate the common bias structure. Second, we used classical logistic regression and mediation analytic methods for dichotomous outcomes to explore the structure of the bias. Lastly, we performed both deterministic and probabilistic sensitivity analysis to estimate the amount of bias due to an uncontrolled confounder and corrected for it. The biased effect of smoking was estimated to reduce the odds of preeclampsia by 28% (OR 0.72, 95%CI 0.52, 0.99) and after stratification by gestational age at delivery (<37 vs. ≥37 gestation weeks) by 75% (OR 0.25, 95%CI 0.10, 0.68). In a mediation analysis, the natural indirect effect showed and OR>1, revealing the structure of the paradox. The bias-adjusted estimation of the smoking effect on preeclampsia showed an OR of1.22 (95%CI 0.41, 6.53). The smoking-preeclampsia paradox appears to be an example of (1) selection bias most likely caused by studying cases prevalent at birth rather than all incident cases from conception in a pregnancy cohort, (2) omitting important confounders associated with both smoking and preeclampsia (preventing the outcome to develop) and (3) controlling for a collider (gestation weeks at delivery). Future studies need to consider these aspects when studying and interpreting the association between smoking and pregnancy outcomes.

Pregnancy-Induced Hypertensive Disorders before and after a National Economic Collapse: A Population Based Cohort Study

BackgroundData on the potential influence of macroeconomic recessions on maternal diseases during pregnancy are scarce. We aimed to assess potential change in prevalence of pregnancy-induced hypertensive disorders (preeclampsia and gestational hypertension) during the first years of the major national economic recession in Iceland, which started abruptly in October 2008.Methods and FindingsWomen whose pregnancies resulted in live singleton births in Iceland in 2005–2012 constituted the study population (N = 35,211). Data on pregnancy-induced hypertensive disorders were obtained from the Icelandic Medical Birth Register and use of antihypertensive drugs during pregnancy, including β-blockers and calcium channel blockers, from the Icelandic Medicines Register. With the pre-collapse period as reference, we used logistic regression analysis to assess change in pregnancy-induced hypertensive disorders and use of antihypertensives during the first four years after the economic collapse, adjusting for demographic and pregnancy characteristics, taking aggregate economic indicators into account. Compared with the pre-collapse period, we observed an increased prevalence of gestational hypertension in the first year following the economic collapse (2.4% vs. 3.9%; adjusted odds ratio [aOR] 1.47; 95 percent confidence interval [95%CI] 1.13–1.91) but not in the subsequent years. The association disappeared completely when we adjusted for aggregate unemployment rate (aOR 1.04; 95% CI 0.74–1.47). Similarly, there was an increase in prescription fills of β-blockers in the first year following the collapse (1.9% vs.3.1%; aOR 1.43; 95% CI 1.07–1.90), which disappeared after adjusting for aggregate unemployment rate (aOR 1.05; 95% CI 0.72–1.54). No changes were observed for preeclampsia or use of calcium channel blockers between the pre- and post-collapse periods.ConclusionsOur data suggest a transient increased risk of gestational hypertension and use of β-blockers among pregnant women in Iceland in the first and most severe year of the national economic recession.

Prevalence of autism spectrum disorders in an Icelandic birth cohort

ObjectivesA steady increase in the prevalence of autism spectrum disorders (ASD) has been reported in studies based on different methods, requiring adjustment for participation and missing data. Recent studies with...

The Relationship Between Birth Weight and Blood Pressure in Childhood: A Population-Based Study

Low birth weight has been associated with increased risk of hypertension later in life. The aim of this study was to evaluate the association between birth weight and blood pressure (BP) in healthy 9- to 10-year-old Icelandic children. Each child underwent 4 seated BP measurements, and the BP percentile was calculated from the mean of the 4 measurements. Height and weight were measured and birth weight retrieved from the Icelandic Birth Registry. Birth measures and anthropometric data were correlated with BP and BP percentiles. Multivariable linear regression was employed to examine the association between BP and birth measures. Of 857 children with complete data, 445 were female (51.9%). The mean BP was 112/64 mm Hg in males and 111/63 mm Hg in females. The mean birth weight was 3714 ± 620 g. No correlation was found between birth weight and absolute BP values. A significant negative correlation between birth weight and both systolic (r = -0.09, P = 0.005) and diastolic (r = -0.08, P = 0.014) BP percentiles was observed. Gestational age did not correlate with BP. In contrast to many previous studies, we found no association between birth weight and absolute BP in children. However, we observed a statistically significant negative correlation between birth weight and BP percentiles. The lack of standardized BP values may partly explain the conflicting results of previous studies in children, and we suggest that BP percentiles be examined more thoroughly in association with birth weight.

No correlation between cesarean section rates and perinatal mortality of singleton infants over 2,500 g

A rising cesarean section rate has been suggested as of benefit in reducing the already low perinatal death rates seen in developed countries for infants of normal birthweight. Iceland has one of the lowest national corrected and uncorrected perinatal mortality rates. Information was collected through the Icelandic birth registry for all 82,251 deliveries of non-malformed singletons weighing > or = 2,500 g at birth, for the 20 years 1987-2006. The mean birthweight-specific perinatal mortality rate for these pregnancies was 2.0/1,000 per year (range 0.8-4.1/1000) without significant changes over the study period. The cesarean section rate varied between 11.9 and 16.7% and did not correlate with the perinatal mortality rate. Among the nulliparous women, cesarean section rates increased from 13.1 to 17.9% without correlation to the perinatal mortality, which on average was 1.7/1,000. A further benefit from rising cesarean section rates at term in countries with a prior low perinatal mortality is questioned.

Congenital cardiac malformations in Iceland from 1990 through 1999

About 1% of live-born children have congenital malformations of the heart. The aim of our study was to investigate the incidence of such defects in children born in Iceland during a period of 10 years, extending from 1990 through 1999. Information about the patients was obtained from medical records from two hospitals that cover the whole country, a private clinic of pediatric cardiologists, an echocardiography database, autopsy reports, and death certificates. We investigated the distribution of specific malformations, the age at diagnosis, the symptoms leading to the diagnosis, the source of referral, and treatment and quality of life. Between 1990 and 1999, there were 44,013 live births in Iceland, of which 740 patients were diagnosed with congenital cardiac malformations, accounting for 1.7% of the live-born children. The distribution was made up of 338 patients with ventricular septal defect (45.7%), 90 with atrial septal defect (12.2%), 85 with patency of the arterial duct (11.5%), 48 with pulmonary valvar stenosis (6.5%), 38 with a bicuspid aortic valve (5.1%), 28 with aortic coarctation (3.8%), 22 with tetralogy of Fallot (3.0%), 14 with transposed great arteries (1.9%), 11 with aortic stenosis (1.5%), 10 with atrioventricular septal defect and common atrioventricular orifice (1.4%), 9 with mitral valvar regurgitation (1.2%), 7 with sub-aortic stenosis (0.9%), and 5 with hypoplasia of the left heart (0.7%). Extracardiac anomalies were seen in 89 patients (12.0%). Chromosomal defects were seen in 36 patients, of whom 28 had Down's syndrome. The annual incidence of diagnosis of patients with congenital cardiac malformations increased during the period of study. This was noted for minor defects, but the incidence of the major anomalies did not alter. Our observed yearly incidence, at 1.7%, was higher than noted in a previous study covering the years 1985 through 1989, and is also higher than in other population-based studies. The most likely explanation is the fact that access to pediatric cardiologists in Iceland is very good. Diagnosis, registration, and follow-up are conducted by only a few cardiologists, and take place at a single center for pediatric cardiology.

Whooping cough and Parkinson's disease. The Europarkinson Preparatory Activity Research Group.

de Pedro-Cuesta J (Instituto de Salud Carlos III, Centro Nacional de Epidemiología, Departamento de Epidemiología Aplicada, c/ Sinesio Delgado, 6, 28029 Madrid, Spain), Gudmundsson G, Abraira V, Gudmundsson G, Lōve A, Tulinius H, Veiga J, Almazán J and Petersen I J for the EUROPARKINSON Preparatory Activity Research Group. Whooping Cough and Parkinson' Disease. International Journal of Epidemiology 1996; 25: 1301–1311.BackgroundWe reported high levodopa use and prevalences of Parkinson's Disease (PD) in periodically, time-clustered, Icelandic cohorts born after major whooping cough epidemics (MWCE).MethodsIn order to quantify a possible relationship between age at first post-birth MWCE and risk of PD we: 1) calculated cumulative incidences of PD during the period 1954–1963 in one-year Icelandic cohorts born between 1869 and 1927, using raw material from a reported survey; 2) identified MWCE from 1869 onwards in Iceland; 3) estimated cohort ages at onset of incidence period and at first MWCE; and 4) combined the above-mentioned information using log-linear models. In addition, we studied the prevalence of levodopa users in Icelandic birth cohorts during a recent period.ResultsThe curves of the above-mentioned incidences and prevalences in one-year birth-cohorts showed: 1) a similar, age-related, inverted V profile; and 2) a systematic notchy pattern, with peak values for one or both measurements for cohorts born during or after each of nine MWCE identified during the period 1869–1927. When 13 cohorts bom in years with MWCE were excluded from the analysis, the risk of PD rose with age at first defined MWCE, with the linear increase being 8.4% per year (95% Cl: −0.1–18.3%).ConclusionsThese results are consistent with reported effects of age at exposure in animal models of toxic parkinsonism, age-related changes in the dopamine receptor-GPT-binding protein-adenylatecyclase system observed in rats treated with pertussis toxin, and some PD epidemiological features. They suggest that pertussis neurotoxicity could be causally related to PD worldwide.