Protein profiles of nasal lavage fluid from individuals with work-related upper airway symptoms associated with moldy and damp buildings.

Upper airway irritation is common among individuals working in moldy and damp buildings. The aim of this study was to investigate effects on the protein composition of the nasal lining fluid. The prevalence of symptoms in relation to work environment was examined in 37 individuals working in two damp buildings. Microbial growth was confirmed in one of the buildings. Nasal lavage fluid was collected from 29 of the exposed subjects and 13 controls, not working in a damp building. Protein profiles were investigated with a proteomic approach and evaluated by multivariate statistical models. Subjects from both workplaces reported upper airway and ocular symptoms. Based on protein profiles, symptomatic subjects in the two workplaces were discriminated from each other and separated from healthy controls. The groups differed in proteins involved in inflammation and host defense. Measurements of innate immunity proteins showed a significant increase in protein S100-A8 and decrease in SPLUNC1 in subjects from one workplace, while alpha-1-antitrypsin was elevated in subjects from the other workplace, compared with healthy controls. The results show that protein profiles in nasal lavage fluid can be used to monitor airway mucosal effects in personnel working in damp buildings and indicate that the profile may be separated when the dampness is associated with the presence of molds.

Vaccination against H1N1 influenza with Pandemrix(®) during pregnancy and delivery outcome: a Swedish register study.

OBJECTIVE: To describe a large study on pregnancy outcome after vaccination against H1N1 during the 2009/10 pandemic. DESIGN: A cohort study of women vaccinated with Pandemrix(®) during pregnancy. SETTING: The Swedish Medical Birth Register was used for the analysis. Information on vaccination and pregnancy week when vaccination was made was obtained from antenatal care documents. POPULATION: All women who gave birth during 2009 and 2010 in Sweden. METHODS: Characteristics of the vaccinated women and their delivery outcome were compared with two groups of women: women without a known vaccination who gave birth in 2009/10 after 1 October 2009, and women who gave birth during 2009 before 1 October. Adjustment was made for year of delivery, maternal age, parity, smoking habits and body mass index. OUTCOME MEASURES: Stillbirth, congenital malformations, preterm birth, low birthweight, small for gestational age. RESULTS: A total of 18 612 vaccinated women having 18 844 infants were studied. The risk for stillbirth, preterm birth and low birthweight was lower than in the comparison groups whereas the risk for small for gestational age and a congenital malformation (after vaccination during the first trimester) did not differ from the comparison groups. No clear-cut explanation to the 'protective' effect of vaccination was found. CONCLUSIONS: Vaccination during pregnancy with Pandemrix(®) appeared to have no ill effects on the pregnancy. On the contrary, the rate of preterm birth and low birthweight was lower than expected, which agrees with some previous results.

Malignancies among women who gave birth after in vitro fertilization.

BACKGROUND: Relatively few studies published to date have investigated IVF and cancer risk. In this study we compared the occurrence of cancer in women who gave birth after IVF with all other women who gave birth in the study period. METHODS: All women who were treated with IVF and gave birth during the years 1982-2006 in Sweden were identified from all IVF clinics, and the occurrence of cancer in these women was identified by linkage with the nationwide Swedish cancer register. Comparison was made with Mantel-Haenszel odds ratios (ORs), adjusting for year of delivery and maternal age, parity and smoking. Cancer before IVF was only studied in first parity women. Specific cancer forms were also studied. RESULTS: Among 24058 women who had been treated with IVF, 1279 appeared in the cancer register. The total number of women studied in the population was 1 394 061, and 95 775 of these were registered in the cancer register. The risk for cancer before IVF was increased [OR 1.37, 95% confidence interval (CI) 1.27-1.48] and was especially high for ovarian cancer (3.93). The risk for cancer after IVF was significantly lower (OR 0.74, 95% CI 0.67-0.82), mainly due to a lower than expected risk for breast and cervical cancer. The risk for ovarian cancer was increased but lower than the risk before IVF (2.13). CONCLUSIONS: Cancer or cancer treatment may increase the risk for infertility leading to IVF. After IVF, in most cases with treatment with fertility hormones, a significantly low cancer risk was found. Ovarian cancer showed an increased risk, although lower than before IVF. One possible reason is ovarian pathology causing both infertility and an increased cancer risk.

Trends in delivery and neonatal outcome after in vitro fertilization in Sweden: data for 25 years.

BACKGROUND: Marked changes have occurred in in vitro fertilization (IVF) methodology during the past 25 years but also in characteristics of couples undergoing treatment. METHODS: This study was based on 27 386 women undergoing IVF treatment from 1982 to 2006 and giving birth to 31 850 infants. Outcomes of deliveries were studied using Swedish health registers. Comparisons were made with all deliveries in the population (n = 2 603 601). Adjusted odds ratios were calculated when important changes in background rates had occurred. RESULTS: There was a substantial increase in the use of intracytoplasmatic sperm injection (ICSI) and the transfer of cryopreserved embryos. Among all ICSI cases, the proportion using epididymal or testicular sperm varied between 5 and 10%. Maternal characteristics changed during the observation period but the median age remained relatively constant in spite of the increasing maternal age in the population. There was a decline in the rate of some maternal pregnancy diagnoses (notably pre-eclampsia, premature rupture of membranes) and some neonatal diagnoses (notably preterm births, low birthweight, cerebral hemorrhage, respiratory diagnoses, use of continuous positive airway pressure and mechanical ventilation, sepsis/pneumonia). Up till 1992, the twinning rate increased to a maximum of about 30% and then declined to 5% towards the end of the period whereas higher order multiples nearly disappeared. The total rate of infants with congenital malformations changed only little. CONCLUSIONS: The decrease in unwanted outcomes can, to a large extent, be explained by the reduced rate of multiple births but was seen also among singletons. Other explanations can be sought in changes in the characteristics of patients undergoing IVF.

Selected neonatal outcomes in dizygotic twins after IVF versus non-IVF pregnancies.

OBJECTIVE: To compare neonatal outcome among twins conceived after in vitro fertilisation (IVF) with that of spontaneously conceived twins. DESIGN: Comparison of different-sex (dizygotic) twins born after IVF with non-IVF dizygotic twins. SETTING: National health registers in Sweden. POPULATION: All births in Sweden during the period 1982-2007. METHODS: We studied gestational duration, lowest birthweight and birthweight difference in the twin pair, presence of one or two twins with a respiratory complication, and with jaundice in one or both twins. Risk estimates were calculated as odds ratios with adjustments for year of birth, maternal age, parity and smoking in pregnancy. MAIN OUTCOME MEASURES: Gestational duration, birth weight, respiratory complications, jaundice. RESULTS: We studied 1545 pairs of dizygotic twins born after IVF, and 8675 pairs of dizygotic twins where IVF was not known to have occurred. The risk for preterm delivery before 32 weeks of gestation was significantly increased among dizygotic twin pairs born after IVF compared with non-IVF dizygotic twin pairs. No significant difference in low birthweight or birthweight difference within twin pairs was seen. There was an increased occurrence of twin pairs with respiratory problems or jaundice, but only the latter diagnosis occurred in a statistically significant excess. CONCLUSIONS: The study confirms recent findings that IVF is associated with an increased risk for some neonatal complications, not only among singletons but also among twins.

Intramuscular pain modulatory substances before and after exercise in women with chronic neck pain.

BACKGROUND: In peripheral tissue, several substances influence pain and pain modulation. Exercise has been found to decrease pain and improve function for chronic pain conditions, but how and why exercise produces beneficial effects remains unclear. This study investigates whether aspects of pain and concentrations of substances with algesic, analgesic and metabolic functions differ between women with chronic neck shoulder pain (CNSP) and healthy women (CON) and whether changes are found after an exercise intervention for CNSP. METHODS: Forty-one women with CNSP and 24 CON subjects were included. The participants attended two microdialysis sessions with 4-6 months between the experiments. During this period, the CNSP subjects underwent an exercise intervention. Expression levels of substance P, beta-endorphin, cortisol, glutamate, lactate and pyruvate as well as pain intensity and pressure pain thresholds were analysed. RESULTS: At baseline, higher concentrations of glutamate and beta-endorphin and lower concentrations of cortisol in CNSP than CON were found. After exercise, decreased levels of substance P and possibly of glutamate, increased levels of beta-endorphin and cortisol as well as decreased pain intensity and increased pain pressure thresholds were found for CNSP. CONCLUSIONS: The findings at baseline indicated algesic and analgesic alterations in the painful trapezius muscles. The findings for CNSP after the exercise intervention, with changes in peripheral substances and decreased pain intensity and sensitivity, could reflect a long-term physiological effect of the exercise.

Maternal smoking in pregnancy: does it increase the risk of childhood cancer?

Experimental studies show that some compounds in tobacco smoke are transplacental carcinogens, but epidemiological data on maternal smoking and childhood cancer are inconclusive. Using the national Swedish Medical Birth and Cancer Registries, the incidence of cancer was followed through 1987 in a cohort of 497,051 children born 1982-1987 for whom information was available on maternal smoking at 2-3 months of pregnancy. A total of 327 cancers appeared including 198 solid tumours and 129 cancers of the lymphatic and haematopoietic system. The overall relative risk for cancer in children with mothers reporting smoking during pregnancy was 0.99 (95% confidence interval (CI): 0.78-1.27). Corresponding risks for solid tumours and cancers of the lymphatic/haematopoietic system were 0.96 (0.70-1.32) and 1.04 (0.71-1.52), respectively. There was no consistent increase in risk for cancer of different sites or in relation to number of cigarettes smoked per day.

Behavioral sensitization to nicotine is associated with behavioral disinhibition; counteraction by citalopram.

This study investigated the effects of repeated nicotine treatment on locomotor activity and behavioral inhibition, and the influence of citalopram on the behavioral effects obtained. Male rats received daily subcutaneous injections of vehicle + vehicle (veh + veh), citalopram (5.0 mg/kg) + vehicle (cit + veh), vehicle + nicotine (1.0 mg/kg; veh + nic) or citalopram + nicotine (cit + nic). Acutely, nicotine stimulated locomotor activity, and repeated daily nicotine injections sensitized veh + nic rats to the nicotine-induced locomotor stimulation after 5, 10 and 15 treatment days, whereas in cit + nic rats, the enhancement of nicotine-induced locomotion was suppressed. However, when challenged with nicotine after citalopram withdrawal (-36 h), the cit + nic treated animals were also observed to be sensitized. In the elevated plus-maze, repeated nicotine treatment produced behavioral disinhibition, measured as an increase of time spent in and entries made into open arms (%), and chronic citalopram treatment attenuated the expression of behavioral disinhibition. Moreover, the degree of nicotine sensitization correlated to the behavioral disinhibition observed. In summary, these findings suggest that behavioral sensitization to nicotine is associated with behavioral disinhibition and that chronic citalopram treatment counteracts the expression of both phenomena. Since citalopram is a highly selective serotonin reuptake inhibitor, the effects of citalopram may be due to a facilitation of serotonin neurotransmission caused by the chronic citalopram treatment.

Behavioral and neurochemical consequences of repeated nicotine treatment in the serotonin-depleted rat.

RATIONALE: Repeated exposure to addictive drugs causes neuroadaptive alterations that are proposed to increase the incentive motivation to consume drugs and to decrease the ability to inhibit such inappropriate motivational impulses and responses. Together, these behavioral consequences of drug intake may underlie the compulsive drug-seeking and -taking behaviors observed in drug abuse. OBJECTIVE: Brain serotonin (5-HT) has been implicated in these mechanisms and this study therefore investigated the consequences of brain 5-HT depletion on the behavioral and neurochemical effects induced by repeated daily nicotine treatment (15 days) in male rats. METHODS: The effects of the present pharmacological manipulations were evaluated behaviorally (locomotor activity, the elevated plus-maze) and neurochemically (microdialysis, brain biochemistry). RESULTS: Depletion of brain 5-HT produced behavioral disinhibition in the elevated plus-maze. In 5-HT-depleted animals, nicotine-induced locomotor sensitization was observed on treatment days 5, 10, and 15, but only on day 15 in the sham-operated rats. Postsensitization, the locomotor stimulatory effects of amphetamine and the dopamine receptor agonists SKF 38,393, apomorphine, and quinpirole were decreased in 5-HT-depleted animals, an effect that appeared to be more pronounced in nicotine-treated rats. Repeated nicotine treatment sensitized the nicotine-induced elevation of the extracellular accumbal dopamine levels in sham-operated, but not in 5-HT-depleted rats, and was also associated with decreased D2 autoreceptor function in both nicotine-treated experimental groups. CONCLUSIONS: Depletion of brain 5-HT, which produces behavioral disinhibition, may slightly facilitate the overall expression of locomotor sensitization to nicotine and differentially affect the pre- and postsynaptic neuroadaptive events involved in the expression of these phenomena.

Neonatal outcome in pregnancies from ovarian stimulation.

OBJECTIVE: To study the neonatal outcome in pregnancies after ovarian stimulation, not including in vitro fertilization. The outcomes studied were multiple birth, preterm birth, and low birth weight among singletons, congenital malformations, and infant death. METHODS: We identified 4029 women who delivered between 1995-1999 after ovarian stimulation alone and compared them with 438,582 women who neither had ovarian stimulation nor in vitro fertilization. We controlled for the confounding effect of year of birth, maternal age, parity, and length of subfertility before the pregnancy. RESULTS: The twinning rate was 5.9% in the study group and 1.2% in the control group. The triplet rate was 0.5% in the study group and 0.02% in the control group. A nearly doubling of the rate of monozygotic twinning was indicated in the study group compared with the control group. There was an excess of singleton preterm births and low birth weight infants in the study group, but this was mainly explainable by confounding of maternal age, parity, and subfertility. The rates of congenital malformations and perinatal deaths were increased, also mainly explainable by maternal characteristics. No increase in specific types of congenital malformations was seen. CONCLUSION: As the deviations in neonatal outcome after ovarian stimulation alone were reduced or disappeared when the confounding of maternal age, parity, and subfertility was taken into consideration, there is probably little direct effect of the stimulation procedure as such.

Determinants of poor pregnancy outcomes among teenagers in Sweden.

OBJECTIVE: To study pregnancy outcomes among teenagers and to determine whether age-related increases in risk are due to differences in socioeconomic conditions, maternal smoking, or anthropometric status. METHODS: All single births during 1990-1991 to mothers aged less than 25 years recorded in the Swedish Medical Birth Registry were studied (n = 62,433). The pregnancy outcomes analyzed were late fetal death, infant mortality, preterm birth, low birth weight, small for gestational age, and low Apgar scores. Information on maternal age, parity, family situation, maternal smoking, maternal height, and weight gain during pregnancy was recorded in the Medical Birth Registry. Information on socioeconomic characteristics was obtained from the Population Census. Logistic regression analysis was used to define the determinants of the adverse outcomes among teenagers. RESULTS: Compared with women aged 20-24 years, girls of 17 years or less were at higher risk for preterm birth (odds ratio [OR] 1.6), and this increased risk remained essentially unchanged after controlling for major confounding factors (OR 1.5). Teenagers also had a crude 50% higher risk of late fetal death and infant mortality, but this risk was reduced after controlling for the effect of socioeconomic characteristics (adjusted OR 1.2). CONCLUSIONS: The increase in risk of late fetal death and infant mortality associated with low maternal age is substantially an effect of teenagers' poorer socioeconomic situation. However, the increase in preterm birth among younger teenagers suggests that young maternal age may be a biologic risk factor for preterm birth.

Nicotinic mechanisms involved in the dopamine activating and reinforcing properties of ethanol.

Ethanol shares with all major dependence producing drugs the ability to activate brain mesocorticolimbic dopamine neurons, an important part of the brain reward systems. This dopamine activation may be involved in mediating the positive reinforcing effects of ethanol. The mechanisms of action of ethanol in its activation of this dopamine system remain, however, to be elucidated. A selective pharmacological interference with these mechanisms may offer a possibility to reduce the reinforcing properties of ethanol without simultaneously interfering with the reinforcing properties of natural rewards. Ethanol has been shown to directly influence the function of various ligand-gated ion-channels. Several of these are located on or nearby mesocorticolimbic dopamine neurons. One such receptor is the nicotinic acetylcholine receptor (nAChR). The present article reviews a series of investigations aimed at investigating whether nAChRs are involved in the dopamine activating and reinforcing properties of ethanol. To this end acute and chronic behavioral and neurochemical experiments were performed in mice and rats. The results obtained indicate that central nAChRs in the ventral tegmental area are involved in mediating the mesolimbic dopamine activating and reinforcing effects of ethanol. Furthermore, the ethanol-induced activation of these receptors is probably indirect, subsequent to a primary interference of ethanol in the nucleus accumbens. Moreover, subchronic nicotine treatment enhances the reinforcing and dopamine activating properties of ethanol. This long-term effect may, however, derive from autonomic adaptations in response to intermittent blockade of peripheral nAChRs (rather than from intermittent stimulation of central receptors), and appears to be associated with development of a disinhibitory behavior that could involve also other neurotransmitters, e.g. serotonin. Taken together, these findings could provide a neurobiological explanation to the often observed co-abuse of nicotine and ethanol in man. Furthermore, since the behavioral models applied previously have predicted therapeutic drug effects in the clinic, the results suggest that selective blockade of the ventral tegmental nAChRs that are involved in the above effects may provide a new pharmacological alternative in the treatment of alcoholism.

Nicotine induces disinhibitory behavior in the rat after subchronic peripheral nicotinic acetylcholine receptor blockade.

The present study investigated the effects of subchronic nicotine, mecamylamine and hexamethonium, alone or in combinations, on locomotor activity and behavioral inhibition. Rats were divided into groups and tested for locomotor activity after acute nicotine. The different groups received vehicle, nicotine, mecamylamine, mecamylamine+nicotine, hexamethonium (two different concentrations) and hexamethonium+nicotine injections once a day for 15 days after which they were tested for nicotine-induced locomotor activity again. Acutely, nicotine stimulated locomotor activity, and repeated daily nicotine or hexamethonium+nicotine administration sensitized the animals to this nicotine-induced locomotor stimulation (locomotor sensitization). Mecamylamine administered subchronically in combination with nicotine was able to block the induction to locomotor sensitization to nicotine. None of the nicotinic receptor antagonists induced locomotor sensitization to nicotine by themselves. In the elevated plus-maze, subchronic nicotine treatment demonstrated a nicotine-induced behavioral disinhibition, measured as an increase of time spent in and entries made into open arms. In contrast to the findings regarding locomotor sensitization, none of the antagonists counteracted the induction of this nicotine-induced behavioral disinhibition after subchronic co-treatment with nicotine. In addition, both antagonists by themselves produced a similar effect as subchronic nicotine, i.e. promoted the development of nicotine-induced disinhibitory behavior. It was concluded that the induction of locomotor sensitization to nicotine involves stimulation of central nicotinic acetylcholine receptors, whereas the development of nicotine-induced behavioral disinhibition involves blockade of peripheral nicotinic acetylcholine receptors, and that the latter, but not the former, phenomenon from a pharmacological point of view appears to be related to the increased ethanol consummatory behavior observed after subchronic nicotine administration.

Nicotine-induced behavioral disinhibition and ethanol preference correlate after repeated nicotine treatment.

This study investigated the effects of repeated daily nicotine (0.35 mg/kg; 15 days) treatment on behavioral inhibition and locomotor activity in the elevated plus-maze and on voluntary ethanol consumption. When challenged with nicotine before the test, rats pretreated with repeated nicotine spent more time on and made more entries onto the open arms of an elevated plus-maze than did vehicle-pretreated animals. The ethanol preference and intake, measured during 3 h after a nicotine injection, was also higher in the nicotine-pretreated animals. In ethanol consumption experiments, there was a positive correlation between the % time and % entries made onto open arms vs. the ethanol preference and intake. However, no correlation between the total number of entries made in the elevated plus-maze and the measures of ethanol consumption was observed. These findings suggest that the ability of repeated nicotine administration to increase ethanol consumption is related to development of a nicotine-induced reduction of inhibitory control rather than development of locomotor sensitization.

Effects of 5-HT1A and 5-HT2 receptor agonists on the behavioral and neurochemical consequences of repeated nicotine treatment.

This study investigated the effects of repeated daily (15 days) treatment with nicotine, alone or in combination with the 5-HT1A/7 receptor agonist (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) or the 5-HT2 receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI) on locomotor sensitization, mesolimbic dopamine neurochemistry and on behavioral inhibition in the rat. Acute nicotine elevated the extracellular dopamine levels in the nucleus accumbens and stimulated locomotor activity, effects that were sensitized after repeated nicotine treatment. Repeated nicotine administration also produced nicotine-induced behavioral disinhibition in the elevated plus-maze. Treatment with DOI counteracted the expression of the nicotine-induced locomotor and neurochemical sensitization, but had no effect on nicotine-induced behavioral disinhibition. Treatment with 8-OH-DPAT decreased the expression of nicotine-induced behavioral disinhibition, but had no effect on locomotor or neurochemical sensitization. Taken together, these findings suggest that the 5-HT1A and the 5-HT2 receptor subtypes are differentially involved in the effects of repeated nicotine on locomotor sensitization, behavioral inhibition and mesolimbic dopamine neurochemistry.

Mortality among the elderly in Sweden by social class.

Total mortality has been analysed for elderly Swedish men and women by social class. Information on social and demographic factors was obtained from the 1960 Population Census. The mortality was followed up from 1961 to 1979. The study indicates that there are evident social class differences in mortality among people aged 65-83 years. We found increasing class differences with increased age among women, but decreasing class differences with increased age among men. Also, the class gradients before retirement age were steeper than after that age. The opposite was true for women, where the class gradient was more evident among older women than among younger ones. The class gradients were less marked for married than for other marital status groups and the class gradients were steepest in areas with a high degree of urbanization.

Effects of serotonergic manipulations on the behavioral sensitization and disinhibition associated with repeated amphetamine treatment.

This study investigated the effects of repeated amphetamine treatment on locomotor activity and behavioral inhibition in the elevated plus-maze, and the influence of serotonin (5-HT) neurotransmission on these behaviors. Acute administration of amphetamine (1.0 mg/kg subcutaneously [SC]) stimulated locomotor activity, which was attenuated by acute citalopram (5.0 mg/kg SC) pretreatment. Repeated daily treatment with amphetamine (15 days) sensitized the rats to the amphetamine-induced locomotor stimulation. Acute pretreatment with the 5-HT precursor l-5-hydroxytryptophan (5-HTP; 25 mg/kg IP) or chronic treatment with the selective 5-HT reuptake inhibitor citalopram (5.0 mg/kg SC, twice daily), did not alter the expression of amphetamine-induced locomotor sensitization. In the elevated plus-maze, animals subjected to repeated amphetamine treatment expressed behavioral disinhibition after amphetamine exposure (1.0 mg/kg SC; -35 min), which was antagonized both by acute 5-HTP and chronic citalopram treatment. In summary, these findings suggest that behavioral sensitization to amphetamine is associated with amphetamine-induced behavioral disinhibition, and that acute 5-HTP as well as chronic citalopram treatment counteract the expression of amphetamine-induced behavioral disinhibition, but not locomotor sensitization. It appears likely that the antagonistic effects of 5-HTP and citalopram on behavioral disinhibition derive from a drug-induced facilitation of brain 5-HT neurotransmission.

Nefazodone attenuates the behavioral and neurochemical effects of ethanol.

This study evaluated the influence of nefazodone, a combined 5-HT2A receptor antagonist and 5-HT reuptake inhibitor, on the behavioral and neurochemical effects of ethanol in nonselected male Wistar rats. In microdialysis experiments, ethanol (2.5 g/kg, i.p.) increased extracellular accumbal dopamine levels by 36% (p = 0.0073) compared to baseline levels, and elevated the maximal DOPAC and HVA levels by 26% (p = 0.0093) and 52% (p = 0.0010), respectively, Nefazodone (50 mg/kg, s.c.) per se increased accumbal dopamine levels by 28% (p = 0.0199) but, when injected 40 min before ethanol, reduced the ethanol-induced elevation of accumbal dopamine overflow (p = 0.0132) and decreased the ethanol-induced HVA levels (p = 0.0159). In an ethanol(6% v/v)/water free-choice paradigm, nefazodone (50 mg/kg, s.c.) decreased ethanol intake by 51% (p = 0.0251) and preference by 22% (p = 0.0251) in high- but not low-preferring rats from a nonselected Wistar strain. These results show that nefazodone modulates the mesolimbic dopamine system in a dopamine activity-dependent manner, and influences the neurochemical and behavioral effects of ethanol in the rat.

Twin births to mothers who are twins: a registry based study.

OBJECTIVES: To estimate the risk of having twin infants for mothers who are twins; to investigate the genetic influence on twinning. DESIGN: Retrospective study of multiple births in two nationwide registries. SETTING: Sweden. SUBJECTS: Multiple births among 31,586 deliveries between 1973 and 1991 to women who were twins. MAIN OUTCOME MEASURES: Numbers of monozygotic and dizygotic twin births expected and estimated. RESULTS: Women who are dizygotic twins have a moderately increased risk of having twins (relative risk 1.30, 95% confidence interval 1.14 to 1.49) which seems to be completely the result of dizygotic twinning. When a mother is a monozygotic twin, her risk of having twins of the same sex is significantly increased (1.47; 1.10 to 1.97). This is the result of an excess of monozygotic twins (39 pairs estimated, 18 expected). CONCLUSIONS: Women who are twins have an increased risk of giving birth to twins. Genetic components of monozygotic and dizygotic twinning seem to be independent.

Social class differences in infant mortality in Sweden: comparison with England and Wales.

OBJECTIVES: To investigate social class differences in infant mortality in Sweden in the mid-1980s and to compare their magnitude with that of those found in England and Wales. DESIGN: Analysis of risk of infant death by social class in aggregated routine data for the mid-1980s, which included the linkage of Swedish births to the 1985 census. SETTING: Sweden and England and Wales. SUBJECTS: All live births in Sweden (1985-6) and England and Wales (1983-5) and corresponding infant deaths were analysed. The Swedish data were coded to the British registrar general's social class schema. MAIN OUTCOME MEASURES: Risk of death in the neonatal and postneonatal period. RESULTS: Taking the non-manual classes as the reference group, in the neonatal period in Sweden the manual social classes had a relative risk for mortality of 1.20 (95% confidence interval 1.02 to 1.43) and those not classified into a social class a relative risk of 1.08 (0.88 to 1.33). In the postneonatal period the equivalent relative risks were 1.38 (1.08 to 1.77) for manual classes and 2.14 (1.65 to 2.79) for the residual; these are similar to those for England and Wales (1.43 (1.36 to 1.51) for manual classes, 2.62 (2.45 to 2.81) for the residual). CONCLUSIONS: The existence of an equitable health care system and a strong social welfare policy in Sweden has not eliminated inequalities in post-neonatal mortality. Furthermore, the very low risk of infant death in the Swedish non-manual group (4.8/1000 live births) represents a target towards which public health interventions should aim. If this rate prevailed in England and Wales, 63% of postneonatal deaths would be avoided.