Is previous use of hormonal contraception associated with a detrimental effect on subsequent fecundity?

BACKGROUND: The effects of contraception on subsequent fecundity are yet to be substantiated. METHODS: A total of 2841 consecutive pregnant women in Hull and Sheffield completed questionnaires inquiring about time to pregnancy (TTP), contraceptive use, pregnancy planning, previous pregnancies, age and lifestyle characteristics of each partner. Outcome measures were mean TTP, conception probability and odds of subfecundity after discontinuing each contraceptive method. RESULTS: TTP following long-term combined oral contraceptive (COC), short-term intrauterine device (IUD) or any duration of injectable use were 2.0-, 1.6-, 3.0-fold longer than TTP after condom use, respectively. Within 6 months of discontinuing COC or injectable use, conception probabilities were 0.86 and 0.34, respectively, whereas those relevant to other methods were not significantly different. All levonorgestrel intrauterine system (IUS) users conceived within 1 month. Relative to condoms, odds of subfecundity after COC, injectable and short-term IUD use were 1.9, 5.5, 2.9, respectively. The effect of COC and injectables was stronger with long-term use, in older, obese or oligomenorrhoeic women. Similar results were obtained after adjustment for potential confounders. CONCLUSIONS: A significant reduction in fecundity occurs after COC, IUD or injectables, which is dependent on the duration of use. The effect of COC and injectables is evident in women with a potentially compromised ovarian function. Use of progesterone-only pills or IUS is not associated with a significant effect.     

Infertility, infertility treatment and twinning: the Danish National Birth Cohort

BACKGROUND: We have previously observed that an increasing time to pregnancy (TTP) is associated with a reduced frequency of twin deliveries in couples not receiving infertility treatment. By using updated information, we assessed the frequencies of dizygotic (DZ) and monozygotic (MZ) twin deliveries as a function of infertility (TTP > 12 months), as well as infertility treatment. METHODS: From the Danish National Birth Cohort (1997-2003), we identified 51 730 fertile couples with TTP 12 months and 5163 infertile couples who conceived after treatment. Information on zygosity, available for part of the cohort (1997-2000), was based on standardized questions on the similarities between the twins at the age of 3-5 years. RESULTS: Compared with fertile couples, the frequency of DZ twin deliveries was lower for infertile couples conceiving naturally (odds ratio 0.4, 95% confidence interval 0.2-0.7) and was much higher for infertile couples conceiving after treatment (17.3, 14.4-20.7). The frequency of DZ twin deliveries decreased with TTP in untreated couples, whereas the frequency of MZ twin deliveries remained constant. CONCLUSIONS: The frequency of DZ twin deliveries decreased with TTP and substantially increased with infertility treatment, whereas MZ twin deliveries remained substantially unchanged.     

Indicators for the total duration of premenopausal endogenous estrogen exposure in relation to BMD

BACKGROUND: Previous studies have shown that age at menopause is an important indicator of duration of endogenous estrogen exposure. The present study investigates whether combining more information on reproductive factors is useful in estimating individual total duration of exposure to endogenous estrogens. METHODS: Bone mineral density (BMD) was used as operational outcome. The study population consisted of 3476 white women living in Eindhoven, The Netherlands, aged 46-57 years, either pre- (n = 2420) or postmenopausal (n = 1056). BMD of the lumbar spine was measured by dual X-ray absorptiometry. Information on reproductive factors was obtained with questionnaires. RESULTS: The number of reproductive years explained 4.8% of the variance in BMD, while age at menopause alone accounted for 3.6%. Duration of lactation or oral contraceptive use did not add to the proportion of variance explained. The effect of reproductive years on BMD was stronger in older women. No significant associations with BMD were found for other reproductive variables. The number of miscarriages in premenopausal women (beta = 0.00760, SE = 0.00357, P = 0.03) explained only 0.16% of the variance in BMD. CONCLUSIONS: We conclude that it is not necessary to use more reproductive factors besides age at menopause and menarche in determining total duration of endogenous estrogen exposure.     

Is previous aberrant reproductive outcome predictive of subsequently reduced fecundity?

BACKGROUND: Effect of past reproductive performance on subsequent fecundity is uncertain. METHODS: A total of 2983 consecutive pregnant women self-completed questionnaires about time to pregnancy (TTP), pregnancy planning, previous pregnancies, contraceptive use, age, and individual/lifestyle variables. Outcome measures were: TTP, conception rates (CR) and, subfecundity odds ratio (OR; with 95% confidence intervals) before and after each outcome of last pregnancy. RESULTS: After miscarriage, TTP was longer than before miscarriage [2.1 (1.4-3.0), P < 0.001] and than TTP after livebirth [OR = 2.1 (1.6-2.6), P < 0.001]. Also subfecundity OR after miscarriage increased [1.7 (1.2-2.4), 1.8 (1.2-2.5), P = 0.001, 0.002 respectively]. This effect was more evident in older and obese women. Compared with livebirth, time to ectopic pregnancy (EP) was longer [OR = 13.8 (1.8-108.5), P = 0.001] but TTP after EP was not significantly different. Subfecundity OR relative to livebirth were 12.8 (3.6-45.0) (P<0.001) before, and 3.9 (1.4-11.0) (P=0.01) after, EP. The CR after EP increased 3-fold (1.1-8.3) over those prior to EP. Time to the terminated pregnancies even without contraceptive failures was shorter than that to livebirth [OR = 0.5 (0.3-0.7), P = 0.001] and than TTP after termination [0.35 (0.1-0.8), P = 0.001]. Also subfecundity OR increased after termination [7.2 (1.8-29.7), P = 0.02]. CONCLUSIONS: Miscarriers should be counselled about short-term reduction in subsequent fecundity, and earlier investigations should be considered in those who have other potential risk factors for reduced fertility. Further studies are required to clarify the relatively favourable effect on fecundity following EP and the relative reduction in fecundity after termination of pregnancy.     

Frozen-thawed embryo transfer: influence of clinical factors on implantation rate and risk of multiple conception.

BACKGROUND: Frozen embryo transfer is an important supplementary procedure in the treatment of infertility. While general information concerning the outcome of frozen embryo transfer has been documented, few studies have addressed the potential of embryo implantation in particular clinical situations. Importantly, the risk of multiple conception following frozen embryo transfer has been poorly documented compared with the information available for fresh embryo transfer. METHODS: This is a retrospective study analysing 3570 frozen embryo transfer cycles (1438 couples) with a view to increasing our understanding of the clinical circumstances that influence the potential for embryo implantation. RESULTS: The overall implantation rate was 9.1%. The characteristics associated with a more favourable implantation rate were the success of the previous fresh embryo transfer cycle, age < 40 years and non-tubal factor aetiology of infertility. Such women had an increased risk of multiple conception. CONCLUSION: Female age, the aetiology of infertility and the outcome of fresh embryo transfer are the most important factors influencing the implantation rate following frozen embryo transfer. A prognostic table has been constructed that may assist with the determination of the optimal number of embryos to be replaced in frozen embryo transfer to provide better individualized counselling and to secure an optimal chance of pregnancy while reducing the risk of multiple conception.     

Regional differences in waiting time to pregnancy among fertile couples from four European cities.

BACKGROUND: A previous European study found a longer time to pregnancy (TTP) among fertile women from Paris compared with women from other Western European countries. A co-ordinated, cross-sectional study of pregnant couples from Denmark (Copenhagen), France (Paris), Scotland (Edinburgh) and Finland (Turku) was therefore undertaken to assess differences in waiting TTP among couples from these cities. METHODS: Pregnant women were invited to participate when they showed up for their first antenatal visit in one of the four centres. Inclusion criteria included that their partner was 20-45 years of age and born in the country in which he was currently living and that the pregnancy was achieved without fertility treatment. Both partners filled in a questionnaire and the man underwent a physical examination and delivered a semen sample (Turku: n = 237, Copenhagen: n = 302, Edinburgh: n = 212, Paris: n = 191). RESULTS: French couples had a decreased probability of conception compared with couples from the other three countries, although only after adjustment for confounders. No significant differences between couples from the three other countries were found. CONCLUSION: The observed geographical differences in TTP remain unexplained and were not due to differences in semen quality, but may be caused by varying exposures to environmental factors or psychological distress. In addition, selection bias due to the low participation rates cannot be ruled out. Future studies examining the causes for geographical differences in TTP are needed.     

Effects of subfertility cause, smoking and body weight on the success rate of IVF

BACKGROUND: We investigated the separate and combined effects of smoking and body mass index (BMI) on the success rate of IVF for couples with different causes of subfertility. METHODS: The success rate of IVF was examined in 8457 women. Detailed information on reproduction and lifestyle factors was combined with medical record data on IVF treatment. All IVF clinics in The Netherlands participated in this study. The main outcome measures were live birth rate per first cycle of IVF differentiated for the major predictive factors. RESULTS: For male subfertility the delivery rate per cycle was significantly lower than unexplained subfertility, OR of 0.70 (95% CI 0.57-0.86); for tubal pathology, the delivery rate was slightly lower, OR = 0.86 (95% CI 0.70-1.01). Smoking was associated with a significantly lower delivery rate was slightly lower; for OR = 0.72 (95% CI 0.61-0.84) and a significantly higher abortion rate compared to non-smoking delivery rates of 21.4% and 16.4%, respectively (P=0.02). Women with a BMI of > or = 27 kg/m2 had a significantly lower delivery rate, with an OR of 0.67 (95% CI 0.48-0.94), compared with normal weight women (BMI > or = 20 and <27 kg/m2). CONCLUSIONS: Both smoking and overweight unfavourably affect the live birth rate after IVF. The devastating impact of smoking on the live birth rate in IVF treatment is comparable with an increase in female age of >10 years from age 20 to 30 years. Subfertile couples may improve the outcome of IVF treatment by lifestyle changes.     

Time trends in waiting time to pregnancy among Danish twins

BACKGROUND: Little is known about time trends in fecundity because few population-based data are available. In a survey among female twins born from 1953 to 1976, their time to pregnancy did not differ from singletons and can be considered to represent the fecundity of the general population. METHODS: Information was collected by interview about waiting time to first pregnancy (TTP) and any periods of subfecundity among both male and female twins born between 1931 and 1952. Trends were analysed by considering the year of birth of the index person (birth cohort effect) or year at which the first attempt started (period effect). RESULTS: Eighty-five percent of male and 81.3% of female eligible twins participated. A total of 1598 male twins and 1653 female twins reported a TTP value and 1671 men and 1715 women had a value for their first attempt to conceive including unsuccessful attempts. No overall trends in either male or female TTP were observed with increasing year of birth or of starting time, after adjustment for confounders, but for attempts fecundity increased among female twins by year of birth or of starting the attempt. A decreasing risk of severe infertility with increasing year of birth or year for start of the attempt was observed among male twins, but this observation was based on only 81 men and was not seen among female twins. CONCLUSION: No decreasing trend in fecundity was observed among Danish twins born between 1931 and 1952 who had completed their reproduction. Female twins had a slight increase in fecundity, and men a decrease in severe infertility. In addition, TTP was apparently well reported and recalled for up to 50 years among both male and female twins.     

Genetic regulation of growth from birth to 18 years of age: The Swedish young male twins study

Growth is a complex process, and only little is known on the genetic regulation of it. We analyzed the effect of genetic and environmental factors on growth in a longitudinal Swedish cohort of 231 monozygotic and 144 dizygotic twin pairs born 1973–1979 with length or height measured annually from birth to age 18. The data were analyzed by two different multivariate variance component models for twin data using the Mx statistical package. At birth and 1 year of age, a substantial part of the variation in length was because of common environment (50 and 57%, respectively) and the effect of genetic factors was minor. After 2 years of age, 91–97% of the variation of height could be explained by genetic differences whereas the rest was because of environmental variation not shared by twins. The genetic correlation between heights at ages 2 and 18 was 0.73 (95% confidence intervals 0.68–0.77) showing that 53% of the genes affecting height at these ages are the same or closely linked; with increasing age the correlation with genetic effects at age 18 become subsequently stronger. Especially in mid‐childhood, growth was largely regulated by the same genetic factors. During puberty new genetic factors started to affect height, but also genetic variation affecting height at previous ages remained. These results suggest that genetic regulation of growth is rather uniform, which is encouraging for further efforts to identify genes affecting growth. Am. J. Hum. Biol., 2008. © 2008 Wiley‐Liss, Inc.     

Risk factors for spontaneous abortion: a case-control study in France.

A case-control study was conducted in seven maternity hospitals in the Paris area in 1988 to evaluate the role of several risk factors in spontaneous abortion. A total of 279 cases and 279 controls were compared for socio-demographic characteristics, reproductive history and for conditions of conception. Prior fetal losses [odds ratio (OR) = 2.30 for n greater than or equal to 2; 95% confidence interval (CI) = 1.17-4.61] and maternal age at pregnancy (greater than 30 years) appeared to be major and independent risk factors of spontaneous abortion. Other factors associated with an increased risk of fetal loss were: geographical or ethnic origin (OR = 2.85 for North African women; 95% CI = 1.58-5.10); psychological problems at the time of conception, either related to the outcome of the pregnancy (OR = 3.08; 95% CI = 0.92-10.25) or unrelated to this outcome (OR = 3.35; 95% CI = 1.41-8.00). The following factors were not associated with spontaneous abortion: gravidity, parity, prior induced abortion, prior sexually transmitted diseases and Chlamydia trachomatis serology, menstrual cycle abnormalities, induced conception cycle and in-vitro fertilization, cigarette smoking, current or past use of combined oestrogen/progestagen pill or intrauterine device. These findings confirm the importance of two risk factors for fetal loss: maternal age and number of prior spontaneous abortions. Two risk factors, ethnic origin and psychological problems at the time of conception are also identified, which require further study.     

Endometrial responses to hormone replacement therapy: the bleeding pattern

Little information is available concerning the response of theendometrium to exogenous sex steroid therapy, particularly inthe post-menopausal state. In this study we examined the variabilityof the bleeding pattern in 103 post-menopausal women receivingcyclical sequential combined hormone replacement therapy (HRT)over 6 months. All patients kept menstrual diary cards to recordthe onset, duration and subjective assessment of the severityof bleeding. We defined a cycle as starting from the commencementof treatment till the day of onset of bleeding. Two groups wereidentified amongst 99 women who experienced bleeding: thosewith a mean cycle length of 29 or more days (late bleeders,n = 50) and those with shorter mean cycle length (early bleeders,n = 49). The former were characterized by less variability incycle length and bleeding that was of shorter duration. Fourwomen experienced no bleeding. There were no significant differencesbetween the two groups in age, year since the menopause, weight,height, body mass index (BMI), parity, or in the previous useof HRT. The only significant difference was in their smokinghabits. This suggests a possible link of a hypo-oestrogenicstate to poor cycle control.     

Helping themselves to get pregnant: a qualitative longitudinal study on the information-seeking behaviour of infertile couples

BACKGROUND: Couples seeking infertility treatment are generally hungry for information about available therapeutic options and how to help themselves achieve pregnancy. This study examined couples' perceptions of the information available from various sources in the context of achieved pregnancy or continuing treatment. METHODS: A 3 year prospective interview study started in April 2004, following couples undergoing infertility treatment at a tertiary fertility clinic at Aberdeen Maternity Hospital. Fifty-four couples were invited to participate. Up to three semi-structured interviews took place, and were analysed thematically using a variation of grounded theory. RESULTS: Twenty-seven couples agreed to participate and of the 25 couples followed up, 11 were diagnosed with unexplained infertility. The age range of the women was 22-41 years. All hoped to be given information on helping themselves to achieve pregnancy, spontaneous or assisted, and 19 of the 25 couples became pregnant. Most couples were dissatisfied with the written and verbal information routinely provided by the fertility clinic because it suggested lifestyle changes they had already attempted to adopt. They sought additional information from the internet, books and magazines. Those who became pregnant were generally empowered by the experience and thought that it had helped them to conceive. Women who were still undergoing treatment however, sometimes became distressed, blaming themselves for failing to follow the lifestyle advice provided. CONCLUSIONS: Couples, especially those diagnosed with unexplained infertility, seek information to help themselves conceive, but only those who succeed find it an empowering experience.     

Effects of Social Attitude Change on Smoking Heritability

Societal attitudes and norms to female smoking changed in Spain in the mid-twentieth century from a restrictive to a tolerant, and an even pro-smoking, posture, while social attitudes remained stable for males. We explored whether this difference in gender-related social norms influenced the heritability of two tobacco use measures: lifetime smoking and number of years smoking. We used a population-based sample of 2285 twins (mean age?=?55.78; SD?=?7.45; 58% females) whose adolescence began between the mid-1950s and the early 1980s. After modeling the effect of sex and year of birth on the variance components, we observed that the impact of the genetic and shared environmental factors varied differently by birth cohort between males and females. For females, shared environment explained a higher proportion of variance than the genetic factors in older cohorts. However, this situation was inverted in the younger female cohorts. In contrast, no birth cohort effect was observed for males, where the impact of the genetic and environmental factors remained constant throughout the study period. These results suggest that heritability is larger in a permissive social environment, whereas shared-environmental factors are more relevant in a society that is less tolerant to smoking.     

Coping with anger-provoking situations, psychosocial working conditions, and ECG-detected signs of coronary heart disease

This study explored the association among coping, psychosocial work factors, and signs of coronary heart disease (CHD) among prison staff (777 men, 345 women). Electrocardiogram (ECG) recordings at rest, health examinations, and a questionnaire were used. A high level of covert coping in men and a low level of open coping in women showed the strongest association with signs of CHD. Among several traditional biological and lifestyle risk factors, only age and systolic blood pressure in men and none in the case of women were significantly associated with CHD signs in the final multivariate regression analyses. A coping style of repressed emotions and actions in anger-provoking situations, independent of traditional risk factors, seems to be associated with a prevalence of ECG signs in male and female prison staff.     

Multiple follicular recruitment and intrauterine insemination outcomes compared by age and diagnosis.

We studied the outcome of our intrauterine insemination (IUI) programme, evaluating female age and diagnosis. One-hundred-and-twenty-six patients less than 36 years of age (mean 30.91 +/- 3.02 years) completed 306 cycles of multiple follicular recruitment (MFR) and timed IUI; 64 patients greater than or equal to 36 years of age (mean 38.36 +/- 2.08 years) completed 166 cycles (total 190 patients, 472 cycles). The male partners' semen was prepared for IUI with wash and swim-up techniques. Diagnostic groups were: male factor (n = 26), idiopathic (n = 33), endometriosis (n = 19), ovulatory disorder (n = 7), other (n = 19) and combined factors (n = 86). Pregnancy rates (% per couple, % per cycle) [overall (31.58, 12.7)] [less than 36 years (38.10, 15.69)] [greater than 36 years (18.75, 7.23)] were greater in the less than 36 years group (P less than 0.025). The probability of conception after three treatment cycles was 0.402 overall, 0.481 for age less than 36 years and 0.252 for age greater than or equal to 36 years. The probability of conception for male factor and idiopathic infertility patients was 0.469 and 0.411 respectively. An age effect was found on pregnancy rates in the idiopathic group only. In conclusion, MFR + IUI is a valuable treatment especially for male factor patients and patients less than 36 years old, with idiopathic infertility.     

Selection of patients suitable for one-embryo transfer may reduce the rate of multiple births by half without impairment of overall birth rates

The aim of the present study was to identify a subset of patients at high risk of multiple birth after IVF and hence suitable for one-embryo transfer, which undoubtedly would reduce the multiple birth rate. This retrospective study included 2107 IVF cycles in which two embryos were transferred. Factors with possible correlation to multiple birth were studied in a multivariate analysis. The factors included background data (female age, previous pregnancies and births, previous IVF cycles, indication for IVF) and IVF cycle characteristics. The following factors were independently predictive of multiple birth: female age expressed a negative correlation while number of good quality embryos transferred was positively correlated. A subset of patients was identified as being at high risk of multiple birth by including age, cycle number and presence of tubal infertility in a model derived from a logistic regression analysis. The rate of multiple births can be reduced from 26% to 13% of all births if one-embryo transfer is performed in selected cases. The total birth rate will decrease from 29% to 25% but may be completely restored by performing one additional one-embryo freeze transfer in high risk patients who do not achieve a term pregnancy.     

Determinants of early follicular phase gonadotrophin and estradiol concentrations in women of late reproductive age.

BACKGROUND: FSH and estradiol measured during the menstrual (basal) phase of cycles predict the success of infertility treatment; but the role of these hormones as markers for ovarian reserve in normal populations needs further study. METHODS AND RESULTS: From a cohort study of depressed and non-depressed women, a subset of 406 non-depressed women between the ages of 36 and 45 years with spontaneous periods were selected and their concentrations and determinants of basal hormones measured at study entry, 6 and 12 months later were described. FSH and LH increased significantly over the 12 months of observation (P 相似文献   

Predictive value of menstrual cycle pattern, body mass index, hormone levels and polycystic ovaries at age 15 years for oligo-amenorrhoea at age 18 years

BACKGROUND: On the question of how to counsel adolescents with irregular menstrual cycles or oligomenorrhoea, no clear answer has been given. Adolescents with oligomenorrhoea especially show endocrine abnormalities and may be at risk for ovulatory dysfunction and the polycystic ovary syndrome in adulthood. METHODS: We followed a cohort of adolescents to document changes in menstrual cycle pattern between ages 15 and 18 years in the general population. RESULTS: Two per cent (2/128) of adolescents with regular menstrual cycles developed oligomenorrhoea, and 12% (17/148) of those with irregular menstrual cycles did so. Fifty-one per cent (34/67) of the oligomenorrhoeic adolescents remained oligomenorrhoeic. Increase in body mass index (BMI), concentration of LH, androstenedione or testosterone, and polycystic ovaries (PCO) were associated with persistence of oligomenorrhoea. In multivariate analysis only a normal to high BMI (>19.6 kg/m(2)) consistently contributed significantly to predict persistent oligomenorrhoea. Glucose:insulin ratio as a marker for insulin resistance was not associated with an increased risk for oligomenorrhoea. CONCLUSIONS: Oligomenorrhoea at age 18 years is better predicted by menstrual cycle pattern at age 15 years than by LH or androgen concentrations or PCO at this age. Not only obese, but also normal weight oligomenorrhoeic, adolescents have a high risk of remaining oligomenorrhoeic.     

Reliability of serial urine HCG as a biomarker to detect early pregnancy loss

BACKGROUND: To examine the reliability of HCG as a biomarker for early pregnancy loss, five experienced researchers independently assessed data from 153 menstrual cycles, determining whether each cycle represented 'no conception,' a 'continuing conception' or a 'conception lost.' METHODS: Urine samples were analysed by immunoradiometric assay using a combination of capture antibodies for the intact heterodimer (B109) and for an epitope common to the beta subunit and the beta core fragment (B204). For each cycle, HCG data were presented as graphs of daily assay results. Summary statistics for HCG assays from 46 women who had undergone bilateral tubal ligation represented baseline values. RESULTS: Pairwise agreement among the assessors for any of the three options ranged from 78-89%. At least three experts agreed for 147 cycles (96%), accounting for 28 conception losses and 19 continuing conceptions. The multi-rater kappa was 0.62 for the conception lost category and 0.68 for continuing conceptions, indicating substantial agreement. CONCLUSION: The main sources of disagreement involved deciding whether there was sufficient information for assessment, interpreting cycle parameters such as cycle length or bleeding event, and interpreting a distinct HCG rise pattern that does not exceed the baseline value obtained from the sterilized women.     

Factors related to allergic sensitization to aeroallergens in a cross-sectional study in adults: The Copenhagen Allergy Study

BACKGROUND: The factors underlying recent increases in the prevalence of respiratory allergy are largely unknown. OBJECTIVE: To assess the association between allergic sensitization and several lifestyle/environmental factors. METHODS: A cross-sectional population-based study of 15-69-year-olds in Copenhagen was carried out in 1990. The participation rate was 77.5% (1112/1435). Different lifestyle/environmental factors (explanatory variables) were defined based on questionnaire data. Dependent (outcome) variables were skin prick test (SPT) positivity or specific IgE positivity to common aeroallergens. Explanatory variables associated with outcome in univariate analysis (P < 0.25) were selected for multivariate analysis. Subsequently, a final model for each dependent variable was obtained by stepwise regression analysis (cut-off for entry/removal of variables: P < 0.1). RESULTS: Male sex, young age, low number of siblings, a positive family history of hay fever and never smoking, were independently associated with both SPT positivity and specific IgE positivity. Furthermore, SPT positivity was positively associated with alcohol consumption (dose-response relationship only), and negatively associated with previous keeping of a dog in the household. The association between alcohol consumption and SPT positivity was mainly due to the consumption of wine and remained after adjustment for educational level. Specific IgE positivity was furthermore associated with body mass index with no apparent dose-response relationship. CONCLUSION: Being male, young age, a positive family history of hayfever, low number of siblings and never smoking, were independently associated with allergic sensitization. In addition, the results indicated a possible relationship of alcohol consumption, body mass index and previous keeping of a dog in the household to allergic sensitization. There is a need for prospective studies of risk factors for respiratory allergy.