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PubMed2003

Shift work and subfecundity: a causal link or an artefact?

AIMS: The Danish National Birth Cohort (DNBC) was used to examine whether shift work is associated with reduced fecundity as estimated by time to pregnancy (TTP). METHODS: From 1 March 1998 to 1 May 2000, 39 913 pregnant women were enrolled in the DNBC. Data on job characteristics and TTP (0-2, 3-5, 6-12, and >12 months) were used for 17 531 daytime workers and 3907 shift workers who had planned the pregnancy. Fecundity odds ratios (ORs) were calculated with 95% confidence intervals using the discrete time survival analysis techniques performed by logistic regression. An OR above 1 expresses a shorter TTP and then a higher fecundity. Potential confounders, such as age at conception, gravidity, prepregnant body mass index, smoking, and alcohol consumption, as well as occupational characteristics, were also included in the model. RESULTS: Fixed evening workers and fixed night workers had a longer TTP. Compared with daytime workers, the adjusted ORs were 0.80 (95% CI 0.70 to 0.92) for fixed evening workers, 0.80 (95% CI 0.63 to 1.00) for fixed night workers, 0.99 (95% CI 0.91 to 1.07) for rotating shift (without night) workers, and 1.05 (95% CI 0.97 to 1.14) for rotating shift (with night) workers. When analysis was restricted to nulliparous women, the estimates remained unchanged. The proportions of unplanned pregnancies and contraceptive failures were higher among fixed evening and fixed night workers. CONCLUSIONS: There was no unequivocal evidence of a causal association between shift work and subfecundity. The slightly reduced fecundity among fixed evening workers and fixed night workers may be mediated by pregnancy planning bias or differential options for sexual contacts.

Circadian Rhythm↗
PubMed2000

Patterns of contraceptive use in 5 European countries. European Study Group on Infertility and Subfecundity.

OBJECTIVES: The use of contraception in Denmark, Germany, Poland, Italy, and Spain is described. METHODS: Data were drawn from a population-based cross-sectional study, the European Study of Infertility and Subfecundity. Interviews were conducted with 6630 women aged 25 to 44 years. Logistic regression was used to estimate the effect of factors associated with contraceptive use. RESULTS: Residents of Northern European countries tended to use more effective methods of contraception than residents of Southern European countries. The use of contraception was generally more common among single women, the more highly educated, those with children, and those with a previous induced abortion. These characteristics were also the main determinants of the use of more effective methods. Periodic abstinence and withdrawal were more common among older women. CONCLUSIONS: The European countries are in different phases of contraceptive practice: in Northern and Western Europe, use of more modern methods has been stable over the past 10 years, whereas these methods are less common in Southern and Eastern Europe. The results suggest the need for information, education, and provision of contraceptive services in Eastern and Southern Europe.

Abortion, Induced↗
PubMed2003

Ultrasound diagnosis of polycystic ovaries in women who have no symptoms of polycystic ovary syndrome is not associated with subfecundity or subfertility.

OBJECTIVE: To evaluate the effect on fertility of the appearance of polycystic ovaries in women who have no symptoms of polycystic ovary syndrome. DESIGN: Case-control study. SETTING: Teaching hospitals in Hull, United Kingdom. PATIENT(S): Women with the appearance of polycystic ovaries on ultrasound and women with normal ovaries. INTERVENTION(S): A questionnaire about previous subfertility, pregnancies, menstrual pattern, features of polycystic ovary syndrome, gynecological history, and individual lifestyle factors. MAIN OUTCOME MEASURE(S): Time to pregnancy (TTP) and relative risk (RR) of subfertility in symptomatic and asymptomatic subgroups of both groups. RESULT(S): Women with PCOs took longer TTP and were significantly less fertile if they were obese (RR = 2.6), had menstrual disturbances (RR = 4.6), hirsutism (RR = 2.5), and/or acne (RR = 2.7). Further reductions in fecundity occurred with an increasing number of symptoms (threefold, sevenfold, and 10-fold longer TTP with two, three, and four symptoms, respectively). The TTP of women with no symptoms was not significantly longer and they were not more likely to be subfertile than women with normal ovaries. These symptoms were not associated with significantly reduced fecundity in women with normal ovaries. CONCLUSION(S): The appearance of polycystic ovaries has been shown to have no significant impact on fertility in women with no symptoms. Appearances alone do not reflect the pathological features of polycystic ovary syndrome, and additional diagnostic criteria should be considered. Obesity, menstrual disturbances, and/or hyperandrogenism are factors associated with subfertility in women with polycystic ovaries.

Acne Vulgaris↗
PubMed1999

Regional differences in waiting time to pregnancy: pregnancy-based surveys from Denmark, France, Germany, Italy and Sweden. The European Infertility and Subfecundity Study Group.

The objective of this study was examine geographical variation in couple fecundity in Europe. The study was based upon all recently pregnant (or still pregnant) women within well-defined geographical areas in Europe (Denmark, Germany, Italy, Sweden and France) at a given time period in 1992. Altogether, 4035 women responded to a highly structured questionnaire. Highest fecundity was found in Southern Italy and Northern Sweden; lowest fecundity was seen in data from the East German centre. Approximately 16% of the study population had a waiting time of more than 12 months to become pregnant. Most of the pregnancies were planned (64%) and approximately 14% were the result of contraceptive failures. The study shows that smoking, body mass index, age and parity did not explain the differences in fecundity found between the centres. Regional differences in fecundity exist and the causes may be genetic or due to variations in behavioural and environmental exposures.

Adult↗
PubMed2000

Body mass index and delayed conception: a European Multicenter Study on Infertility and Subfecundity.

Obesity has become a health problem in affluent societies, but few studies have investigated its effect on subfertility. Previous studies were based on select groups of women, focused mainly on ovulatory dysfunctions, and yielded controversial results. The authors evaluated the effect of body mass index on delayed conception by using a European population-based survey of pregnant women from five countries. Delayed conception was defined as a time to pregnancy that exceeded 9.5 months of unprotected intercourse. During 1992, 4,035 pregnant women from well-defined geographic areas were recruited consecutively at antenatal clinics or hospitals after at least 20 weeks of gestation. For women smokers, after adjustment for sociodemographic, biologic, and lifestyle-related factors, there was a strong association between obesity (body mass index of > or =30 kg/m2) and delayed conception (odds ratio = 11.54, 95% confidence interval: 3.68, 36.15) and also an increased risk for women whose body mass index was <20 kg/m2 (odds ratio = 1.70; 95% confidence interval: 1.01, 2.83). The same analysis conducted for women nonsmokers showed no association. The authors concluded that for women who achieve a clinically detectable pregnancy, those who are underweight or obese require a longer time to conceive only if they also smoke.

Adult↗
PubMed1997

The performance of several indicators in detecting recall bias. European Study Group on Infertility and Subfecundity.

Self-reported exposure data are vulnerable to differential recall, which threatens the internal validity and thus the credibility of the study. When a proxy measure of the exposure of interest is available, it may be possible to check for the presence of recall bias due to misclassification of the exposure information. We present a number of indicators of recall bias for case-control studies, and we describe their behavior by means of computer simulations. The indicators are all based upon a comparison between self-reported exposure data and data on job titles grouped into exposure-specific matrices. The indicators are based upon the assumption that job titles are reported without differential misclassification for cases as well as controls. We also assume that exposure data are reported with the same accuracy by workers in different jobs. Under these assumptions, the proposed indicators will provide valuable-although not conclusive-signs of recall bias. The principles elaborated in this paper can be applied to other situations in which self-reported exposure data are used.

Bias↗
PubMed2000

Retrospectively sampled time-to-pregnancy data may make age-decreasing fecundity look increasing. European Infertility and Subfecundity Study Group.

The retrospective study based on pregnancy samples is the most commonly used method for studying time to pregnancy. Using a simple Monte Carlo simulation, this note focuses on a particular selection bias problem associated with this design: even if each woman's fecundity decreases with age, estimation of the effect of age may show the opposite trend. We recommend exercising increased caution in interpreting findings from pregnancy-based time-to-pregnancy studies.

Adult↗
PubMed1993

The risk of male subfecundity attributable to welding of metals. Studies of semen quality, infertility, fertility, adverse pregnancy outcome and childhood malignancy.

These studies were initiated by the results of two Danish investigations of infertility clients, which indicated the reduced fecundity of male metal welders. The objective was to refute or corroborate the effects of welding on male reproductive capability and--if there was any effect--to identify the causal exposures. The initial hypothesis postulated reduced spermatogenesis, spontaneous abortion, congenital malformation and childhood malignancy following exposure to hexavalent chromium among stainless steel welders. Subsequently, a hypothesis concerned with the significance of exposure to radiant heat on reduced semen quality was put forward. These studies comprised a case-referent study of infertility, cross-sectional and longitudinal studies of semen quality and historical cohort studies of fertility, pregnancy outcome and cancer in offspring. Exposure to welding was reported with a higher frequency during periods of infertility than prior to conception in the case-referent study (OR 2.0, 95% CI 1.0-4.0). This finding is consistent with the main cross-sectional study showing reduced semen quality in welders [average reduction ranging from 8% (sperm penetration rate in eggwhite) to 28% (total sperm count)] and with the cohort study revealing reduced fertility in relation to welding (OR 0.89, 95% CI 0.83-0.97). However, reduced semen quality and fertility were not attributable to the welding of stainless steel but to the welding of mild steel; and no relationship was found between biological measures of exposure to chromium and parameters of semen quality. If the unexpected association between mild steel welding and reduced fecundity is causal, the biological mechanisms involved are obscure. A separate longitudinal study leaves little doubt that moderate radiant heat exposure may cause reversible deterioration of semen quality, but it is not justified to generalize this observation to the entire population of welders. Male-mediated effects on occurrence of congenital malformation and cancer in offspring from stainless steel welding are not indicated by the studies. Weak indications of an increased risk of spontaneous abortion among partners to stainless steel welders (OR 1.9, 95% CI 1.1-3.2) need to be refuted or corroborated in future studies. Suggested effects of mild steel welding on male fecundity should be corroborated by longitudinal controlled studies of semen quality examined before and during exposure and by prospective studies of fecundability in couples trying to conceive a child. On account of the present knowledge it is not possible to recommend rational preventative measures with the exception of elimination of radiant heat exposure in cases of infertility.(ABSTRACT TRUNCATED AT 400 WORDS)

Cohort Studies↗
PubMed1994

The association between birth weight, placenta weight, pregnancy duration, subfecundity, and child development.

It is well known that very low birth weight and preterm birth are risk indicators for delayed child development. It is the purpose of this study to estimate the association between birth weight, placenta weight, and gestational age in consecutive pregnancies which survived till after 28th week of gestation. The association between fecundity and child development is also studied. Data stem from pregnant women in a well defined regional area in Denmark (Odense) who participated in a concerted action on moderate alcohol consumption in pregnancy (EuroMac). All pregnant women with an alcohol consumption of 5 drinks or more per week or more in the first trimester were selected for the study in 1988 to 1989. A one to one match of pregnant woman was selected among the remaining pregnant woman based upon expected time of delivery and age. Altogether 326 women were selected for the study and the two groups are combined since alcohol intake in the measured dose range had no association with child development. The newborn went through two psychological tests at 18 month (the Bayley test) and again at 42 months of age (the Griffiths' test). Two hundred fiftynine pairs of mothers and children participated in all parts of data collection. Birth weight and gestational age was associated with the psychological scoring in the test performed at 18 and 42 months of age, especially the psychomotor index. Especially newborns with low birth weight and high placenta weight had low score values on mental development indices. No association was seen between a measure of fecundity (waiting time to pregnancy) and reduced child development.

Adult↗
PubMed1996

Seeking medical help for subfecundity: a study based upon surveys in five European countries.

OBJECTIVE: To study care-seeking behavior for infertility treatment in different European countries. DESIGN: Multicenter surveys of randomly selected women in the child bearing age. SETTING: Five countries participated in the study: Denmark, Germany, Italy, Poland, and Spain. Data were collected from 1991 to 1993 as part of a concerted action. PATIENTS: Population-based samples of women 25 to 44 years of age. The sample sizes ranged from 442 women in Poland to 2,729 in Italy. Participation rates ranged from 54% in Germany to 87% in Denmark. Data were collected by means of a highly structured questionnaire used at a face-to-face interview. MAIN OUTCOME MEASURES: Waiting time to pregnancy, time, and type of treatment for infertility. RESULTS: Less than half of the infertile couples seek medical help in most European countries. The lowest proportion seeking help was found in Poland and the highest in Denmark. CONCLUSION: The increasing demand for infertility treatment is expected to continue, because the potential unmet need is outspoken in most European countries.

Adult↗