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Study Objective: The aim was to study changes in smoking habits during pregnancy and differences in characteristics between women who stop smoking and those who continue to smoke during pregnancy., Design: The study was a population based prospective study. Self administered questionnaires were completed on three occasions., Setting: The study area was Uppsala county, Sweden, in 1987., Participants: The participants were women registered with antenatal care clinics, which included all pregnant women in the county. Ninety six percent (n = 3678) of all pregnant women completed the first questionnaire. Thirty two percent of these were smokers at time of conception., Measurements and Main Results: Twenty nine percent of the smokers stopped smoking at some stage of pregnancy, and the majority did so before having registered for antenatal care. Using logistic regression analysis it was found that high parity number, not living with infant's father, heavy smoking, and daily passive smoking at home were associated with significantly increased risk for continued smoking during pregnancy. High level of education and high age at onset of smoking decreased the risk., Conclusions: In order to reduce the smoking related risks for unsuccessful pregnancy outcome, general preventive efforts in society must be combined with the development of more specialised antenatal programmes designed with consideration of the characteristics and life situation of the pregnant smoker.

The advantages and limitations of national registers containing individual identification numbers in clinical epidemiological research are reviewed. The author concludes that such registers are very valuable for epidemiological research and for formulation of research questions of public health importance.

Several large epidemiological studies in the Nordic countries have failed to confirm an association between age at first birth and breast cancer independent of parity. To assess whether lack of power or heterogeneity between the countries could explain this, a meta-analysis was performed of 8 population-based studies (3 cohort and 5 case-control) of breast cancer and reproductive variables in the Nordic countries, including a total of 5,568 cases. It confirmed that low parity and late age at first birth are significant and independent determinants of breast-cancer risk. Nulliparity was associated with a 30% increase in risk compared with parous women, and for every 2 births, the risk was reduced by about 16%. There was a significant trend of increasing risk with increasing age at first birth, women giving first birth after the age of 35 years having a 40% increased risk compared to those with a first birth before the age of 20 years. Tests for heterogeneity between studies were not significant for any of the examined variables. In the absence of bias, this suggests that several individual Nordic studies may have had too little power to detect the weak effect of age at first birth observed in the meta-analysis.

Body height and weight in relation to breast cancer in women younger than 45 years were investigated in a case-control study in Sweden and Norway. The study included 317 Swedish and 105 Norwegian cases diagnosed in 1984-85 with 317 Swedish and 210 Norwegian age-matched population controls. Neither height nor body size, measured as body mass index, was associated with breast cancer. Change in body mass from the age of 20 years to 18 months before the time of diagnosis (cases) or interview (controls) had no effect on breast cancer risk. The study provides no evidence that anthropometric measures are risk factors for breast cancer in young women, indicating that the postulated inverse relationship between body mass index and pre-menopausal breast cancer could be limited to peri-menopausal women.

A population-based case-control study was conducted in Sweden and Norway to analyse possible associations between breast cancer occurring before the age of 45 and several different characteristics of the women's reproductive life. A total of 422 (89.2%) of all eligible patients, and 527 (80.6%) of all eligible controls were interviewed. In univariate analyses, different characteristics of child-bearing (parity, age at first birth, years between last birth and diagnosis, duration of breast-feeding, and number of induced and spontaneous abortions), measures of the fertile or ovulating period (age at menarche, years between menarche and first pregnancy, and estimates of the menstruation span) and symptoms of anovulatory cycles or infertility were all seemingly unrelated to, or at most weakly associated with breast cancer. Adjustment for possible confounding factors in multivariate analyses resulted in largely unaltered risk estimates with odds ratios close to unity and without any significant trends when the exposure variables were studied in categorised or in continuous form. We conclude that reproductive factors did not explain the occurrence of breast cancer before the age of 45 in this population.

We have analysed the duration of pregnancy for singleton births in Sweden during 1976-80 by means of data from the Swedish Birth Registry. Information, which was obtained from special forms with standard questions, include date of first day of last menstrual period (LMP) and whether that date was considered reliable or not. Recording was done prospectively, starting at the first antenatal visit. In 10% of cases the dates were labelled uncertain. Information on LMP and birth dates, parity, age of mother, sex of child, and/or mode of delivery was missing in 5.5% of the singleton cases, leaving 427,581 singleton births for analysis. In cases of reliable menstrual dates, the average duration from LMP to vaginal birth was 282 days (median), 281 days (mean) and 283 days (mode), remaining constant over the years of study. One standard deviation of the mean was approximately 13 days, varying slightly with age and parity. Ten per cent of these women gave birth post term (past 294 days). The duration of cesarean section births became shorter over the years, in spite of little change in cesarean section frequency (9.5% in 1976-7 and 10.9% in 1979-80). Mothers aged 35 and over tended to give birth 2 days earlier than those below 35. Second and subsequent children of mothers below 35 had slightly shorter gestations than first-borns. Boys were born earlier than girls, on average. When LMP was unreliable, the distribution of gestational lengths was wide. We also noted a seasonal rhythmicity in average duration of pregnancy, with consistent shortening in the month of December.

A total of 44,300 cases of prostatic cancer, comprising 90% of all newly diagnosed cases reported to the Swedish Cancer Registry in 1960 through 1978, constituted a cohort followed up for 1-19 years. Survival rates were adjusted for expected mortality in the general population, and were expressed as relative survival (RS). RS for the total cohort after 5, 10 and 15 years was 51, 34 and 24%, respectively, with an annual excess death rate of about 8% which persisted also after long-term observation. RS was similar in the age groups between 45 and 74 years, whereas among patients older than 74 at diagnosis, approximately 10% lower RS appeared early and was persistent. These data demonstrated that the highly varying natural course of prostatic cancer is only slightly related to patient age at diagnosis. The low long-term relative survival rate definitely contradicted the concept that biologically inactive (latent) tumours constitute a significant proportion of the prostatic cancers diagnosed in clinical practice.

A Swedish-Norwegian case-control study comprising 473 women less than 45 years old with newly diagnosed invasive breast cancer diagnosed in 1984-85, and 722 age-matched control women, was reanalyzed to evaluate if nulliparous women who had used oral contraceptives (OCs) were at particular risk for breast cancer. The relative risk for nulliparous women who had used OCs for eight years or more was 4.3 (95% confidence interval, 1.4-13.1), and parous women with the same duration of use had relative risk 1.7 (0.7-4.2) as compared to nulliparous and parous women, respectively, who had never used OCs. Parous women who had used OCs for twelve years or more after their first full-term pregnancy had a relative risk of 3.0 (1.3-7.4). The findings from the study suggest that nulliparous women may be particularly susceptible to the risk for breast cancer with long-term OC use.

Risk factors for late fetal death and early neonatal mortality were examined in a population based prospective study. Practically all Swedish births between 1983 and 1985 were included, 281,808 births in all. The overall rates of late fetal death and early neonatal mortality were 3.5 and 3.1 per 1000, respectively. About 30% of the pregnant women were recorded as being daily smokers. Logistic regression analyses showed significant relative risks for late fetal death for high maternal age (1.4), nulliparity (1.4), multiparity (greater than or equal to 2) (1.3), smoking (1.4), and multiple births (2.8). Significant relative risks for early neonatal mortality were found for multiple births (4.9) and smoking (1.2). Smokers aged under 35 faced a relative risk of late fetal death ranging from 1.1 to 1.6, while the risk for late fetal death was doubled if the mothers were aged 35 years or more and smoked. In countries like Sweden, where maternal cigarette smoking is prevalent, smoking may be the most important preventable risk factor for late fetal death.

A medical birth registry was used for a geographical analysis of birth weight distribution. Nearly 900,000 Swedish singleton births, 1973-1981, were used for an analysis of the effect of some variables and for standardization for these variables. A marked change in the rate of low birth weight infants (LBW, less than 2,500 g) was seen in the country between 1976 and 1977. A U-formed effect of maternal age and of parity was demonstrated. A marked interaction between the effects of these two variables existed. Two social groups were compared and the well-known high rate of LBW infants associated with low socioeconomic conditions was demonstrated. Standardization for the variables mentioned influenced this effect only little but reduced the difference between the social groups concerning infants above 3.5 kg weight. The background data were used for analysis of restricted geographical areas.

Using data from the Swedish Medical Birth Registry, we examined whether reproductive history influenced pregnancy outcomes among women aged 30 to 39 years who gave birth to a first or second child in 1976 through 1980. They were classified group 1, primigravida; group 2, gravida 2, para O; and group 3, gravida 2, para 1. Compared with women aged 20 through 24 years with the same parity and gravidity, the relative risk (RR) of late fetal deaths was significantly greater among those aged 35 through 39 years (RR: group 1 = 1.76, group 2 = 2.22, and group 3 = 2.39). The risk of giving birth to newborns who were low birth weight and preterm, or low birth weight at term, or 2,500 g or greater but preterm was greater among women aged 30 through 39 years in groups 1 and 2--significantly so for group 1 aged 30 through 39 years v group 1 aged 20 through 24 years. Risk increased with maternal age, from 30 through 34 to 35 through 39 years. The increased risk with age and parity-gravidity has ramifications for the increasing rate of delayed childbearing in the United States and elsewhere.

Epidemiological findings suggest that gallstone disease and some frequent human cancers share common risk factors. In the present historical prospective cohort study, comprising 16,773 patients who had undergone cholecystectomy 12-15 years previously, the risk of developing gastric cancer was investigated. The total number of observed gastric cancers (89) was very close to the expected number (88), giving a relative risk (RR) of 1.01. A significantly increased risk (P less than 0.01; RR = 2.67) of developing gastric cancer was found during the first year after cholecystectomy, and this increase was judged to be due to cancers that were present but overlooked at the time of cholecystectomy. Subgrouping according to age at surgery revealed a tendency towards a lower risk in patients operated on before the age of 70 years. It is concluded that our data do not support the hypothesis that there are common risk factors for gallstones and cancer, and cholecystectomy does not seem to be associated with an increased risk of gastric cancer within 15 years after this operation.

An increase in induced abortions in Sweden has been accompanied by an increase in the incidence of breast cancer of about 40% in women aged 20-44. To assess whether the apparent risk is real the risk of breast cancer was investigated in practically all Swedish women with a history of a legal abortion in the first trimester before the age of 30 during 1966-74 (n = 49,000). The cohort was followed up in the Swedish cancer register to identify cases of breast cancer diagnosed more than five years after the abortion until the end of 1984. The number of observed cases of breast cancer was 65 compared with an expected number of 84.5, estimated from the contemporary Swedish population with due consideration to age, giving a relative risk of 0.8 (95% confidence interval 0.58 to 0.99). Contrary to most earlier reports, this study did not indicate any overall increased risk of breast cancer after an induced abortion in the first trimester in young women.

The possible association between oral contraceptive (OC) use and the risk of breast cancer developing before the age of 45 was investigated by means of a population based case-control study in Sweden and Norway. Information was obtained by personal interview from 422 (89.2%) of all eligible patients with a newly diagnosed breast cancer from May, 1984, to May, 1985, and from 722 (80.6%) of all contacted age-matched controls. A multivariate analysis, which accounted for several possible confounding factors, revealed a significant (p = 0.03) association between total duration of OC use and breast cancer risk. The relative risk (RR) of breast cancer after 12 or more years of OC use was 2.2 (1.2-4.0). OC use for more than 7 years before first full-term pregnancy entailed an increased breast cancer risk (RR = 2.0 [1.0-4.2]) which was of borderline significance. When total duration of use was considered, the risk of breast cancer was virtually unrelated to age at first OC use and latency from first use. The results suggest that long-term use of OCs may increase the risk of breast cancer in young women.

We followed for 25 to 33 years 6459 patients who had undergone partial gastrectomy for benign ulcer disease to determine the incidence of stomach cancer. The overall risk was no different from that among sex- and age-matched controls from the Swedish Cancer Registry (standardized incidence ratio = 0.96; 95 percent confidence limits, 0.78 and 1.16). However, when the patients were classified according to the duration of follow-up after operation, sex, surgical procedure, diagnosis at the time of operation, and age at operation, differences in risk were observed between the subgroups. After adjustment for potential confounding variables, the average adjusted risk increased 28 percent (adjusted standardized incidence ratio = 1.28; 95 percent confidence limits, 1.11 and 1.49) for each successive five-year interval after operation. The adjusted risk was greater among women than men (adjusted standardized incidence ratio = 1.96; 95 percent confidence limits, 1.18 and 3.24). Patients who had undergone a Billroth I anastomosis had a lower crude risk, both overall (standardized incidence ratio = 0.40; 95 percent confidence limits, 0.20 and 0.71) and after we controlled for other confounding variables (adjusted standardized incidence ratio = 0.27; 95 percent confidence limits, 0.12 and 0.62), than did those who had undergone a Billroth II procedure. The adjusted risk of stomach cancer was greater among patients operated on for gastric ulcer than among those operated on for duodenal ulcer (adjusted standardized incidence ratio = 2.21; 95 percent confidence limits, 1.45 and 3.35). Risk decreased with increased age at operation. Between successive strata of age at operation (less than 39, 40 to 49, 50 to 59, and greater than or equal to 60 years of age), the adjusted risk decreased on the average by about half (adjusted standardized incidence ratio = 0.52; 95 percent confidence limits, 0.41 and 0.66).

From 1961-66 to 1973-78 in Uppsala county, Sweden the overall incidence rate of ectopic pregnancy rose from 0.31 per 100 notified pregnancies or 0.28 per 1 000 women 15-44 years of age, to 1.00 and 0.96, respectively. The impact of demographic changes on the increase in the overall incidence was studied. By using indirect age standardization it was found that 13% of the increase in the overall rate of ectopics per 1 000 women was attributable to a change in the age distribution of women in the fertile age-span.

A cohort comprising 11678 women who had undergone cholecystectomy in the period 1964 through 1967 for a benign gallbladder disease was investigated. They represented almost a total ascertainment from a defined geographic area. Follow-up during 11-14 completed years of observation revealed a total of 202 breast cancer cases after the cholecystectomy. This number was close to the expected incidence of 199.1 (relative risk 1.0). Further analysis of the risk in relation to duration of observation and age at operation did not reveal any trend or subgroup with a significantly increased or decreased risk. It was concluded that despite the many epidemiologic observations indicating that in Western Countries dietary habits are particularly important determinants of the high incidence of both gallstone disease and breast cancer, our results contradict the idea that the diseases share common aetiologic factors.

In a well defined geographical area with only one hospital, the incidence of upper urinary tract stone was found to be 180 per 100 000 inhabitants, a figure not substantially higher than that reported more than 30 years ago. The male/female ratio was 3.6:1. The mean frequency of recurrence was 40% and the mean frequency of infection 12%. Hyperparathyroidism was found in 1.4% of all cases. Thirty-five per cent of the patients required hospital treatment and 19% needed operation. Renal pelvic stone was more common in the female (22%) than in the male (8.5%) patients. Spontaneous passage of stone occurred in 87.5% of the men and in 81.5% of the women. No seasonal variation in the onset of acute pain was demonstrable.

This study originated in observations in cohort studies that women who worked in laboratories during pregnancy may be at increased risk of having an infant with gut atresia. A case-control study has been made of 201 women who had infants with gastrointestinal atresia and 402 women with infants without that malformation but matched for age, parity and time of year for delivery. Maternal occupation during pregnancy was ascertained by interviews of mailed inquiries and only referred to type of occupation; no efforts to obtain detailed information on occupational exposure were made. Occupation of nonresponders was checked using census data. In the case-control study, laboratory work was reported to occur more often among case mothers than among controls, thus verifying the connection. The actual exposure in the laboratory work giving the embryonic damage is not known.

During a period of 4 years, 1974-77, in Uppsala county; Sweden, 203 women underwent surgery for ectopic pregnancy with histological proof of the diagnosis. For the female population of fertile age this corresponds to 0.11 ectopics per 100 women 15-44 years of age, or 1.08 per 100 notified pregnancies, or 1.53 per 100 births. Fifty-five of the women with ectopic pregnancy were using an intrauterine device (IUD) (48 a copper-bearing IUD and 7 some other type of device), and 6 women used a low dose progestogen contraceptive. For users of copper-bearing IUDs the risk of an ectopic pregnancy was estimated to be 0.15 per 100 women years. When comparing this latter risk rate with the overall incidence rate of 0.11, it must be observed that the populations forming the denominator in these two rates differ with respect to some crucial characteristics. Nulliparity and predisposing factors were found statistically significantly more often in non-IUD-users with an ectopic pregnancy than in IUD-users. Such predisposing factors may be less prevalent in IUD-users, as in other populations. This may explain why ectopic pregnancy has been found to occur less frequently than theoretically expected among IUD-users. The "ectopic preventing" capacity of the IUD may therefore be considerably lower than has been previously claimed.

Using the Swedish Medical Birth Registry for 1983 the birthweights were studied from the 38th to the 42nd week of gestation. Several criteria were used in order to retain a "normal" population of infants without signs of pathology. The mothers all negated smoking. Of about 93 000 livebirths roughly 10% fulfilled the criteria. Both in the infants who were the first-born child (n = 5.640) and in those who were the second-born child (n = 3.599) there was a successively higher mean birthweight for each completed week until 41 weeks. After that a graph connecting the mean values showed a significant flattening.

A study was made on how the shift in the age and parity distribution of mothers affected the perinatal mortality in Sweden between 1953-55 and 1973-75. During these years the overall perinatal mortality rate fell from 29 to 13 per 1 000 births. The authors used the specific perinatal mortality rates by the mother's age and infant's birth order in 1973-75 to calculate what the overall perinatal mortality rate would have been with the age and parity distributions of mothers in 1953-55 and 1963-65. They conclude that only 1.4 of the 16 per 1 000 decline in perinatal mortality could be attributed to the shift in the mother's age and parity distribution.

Different use of oral contraceptives (OCs) in relation to reproductive histories and age might explain the conflicting results found in studies from different countries of OC use and premenopausal breast cancer. A population-based case-control study in Sweden and Norway has been analysed separately for the two countries. The study consists of 317 Swedish and 105 Norwegian cases diagnosed 1984-1985 with 317 Swedish and 210 Norwegian controls. The results for each country separately are consistent with the joint analysis showing increased risk for breast cancer with increased duration of OC use with the exception of that for women with more than 15 years since first use. The relative risk of breast cancer for more than four years of use among Norwegian women was 0.6 (95% confidence internal (Cl), 0.2-1.8). In both countries there was a non-significant higher risk associated with increasing duration of use before first full-term pregnancy. Analyses for surveillance bias show no evidence of bias as explanation for the association between total duration of OC use and breast cancer.

In a historical prospective study covering 1970-1978, the authors evaluated the outcome of delivery to 429 parous women subsequent to a legally induced first-trimester vacuum-aspiration abortion during 1970-1975 in Uppsala County, Sweden. This outcome was compared with the outcome of delivery to 391 randomly chosen matched parous women and that of all parous women in Sweden in 1975. Confounding variables were controlled for in multiple regression analysis using infant birth weight and gestational duration as dependent variables. In this analysis, no harmful effects of vacuum-aspiration abortion were found. Pre-term deliveries and low birth weight infants did not occur more frequently after such abortions. The study did not disclose any association between vacuum-aspiration abortion in parous women and an unfavorable outcome of subsequent delivery.