Biomedical subjects
Publications and source records attributed to O Meirik.
This paper summarizes findings from epidemiological research in fertility regulation which have helped in formulating policies nationally and internationally, without pretending to be all-encompassing; rather, it should help in demonstrating the usefulness and importance of epidemiological research and in discussing outstanding issues of public health relevance.
BACKGROUND: Although depot medroxyprogesterone acetate (DMPA) (Depo-Provera) has now been approved for marketing as a contraceptive in the United States, there are still unresolved issues about the relation between DMPA and risk of breast cancer. The two substantial case-control studies of this association yielded similar but inconclusive results. Because their designs were compatible, these studies were pooled to obtain more adequate data for analysis. DESIGN: Pooled results from two case-control studies. SETTING: New Zealand (entire country), Thailand (three centers), Mexico (one center), and Kenya (one center). PARTICIPANTS: A total of 1768 women with breast cancer and 13,905 controls, most of whom were younger than 55 years. MAIN OUTCOME MEASURE: Relative risk (RR) of breast cancer in women who had used DMPA. RESULTS: The RR of breast cancer for women who had ever used DMPA was 1.1 (95% confidence interval [CI], 0.97 to 1.4). There was no increase in risk with increasing duration of use of DMPA, but RR estimates were higher in certain subgroups of women. Further analyses suggested that recent (or current) use was the key factor, with women who had started using DMPA within the previous 5 years estimated to have an RR of 2.0 (95% CI, 1.5 to 2.8). CONCLUSIONS: The increased risk of breast cancer observed in recent (or current) users could be due to enhanced detection of breast tumors in women using DMPA or to acceleration of the growth of preexisting tumors. Women who had used DMPA more than 5 years previously had no increase in risk of breast cancer, regardless of their duration of use.
The aim of this study was to examine associations between oral contraceptive (OC) use, body mass index (BMI = weight/height2) and prognosis in invasive breast cancer diagnosed before the age of 45. Survival analyses of a consecutive sample of breast cancer patients were undertaken. The cases were initially registered in a nationwide case-control study of OC use and risk of premenopausal breast cancer in Sweden and Norway. All 422 cases were under 45 years of age at diagnosis, and recruited from the reports to cancer registries (Sweden) or from surgical departments (Norway) during May 1984 through May 1985. Detailed information about OC exposure was obtained in the initial face-to-face interview. With Cox's proportional hazards analyses, a significantly lower hazard rate [relative hazard (RH) = 0.54; 0.31-0.94] was seen in short-term users (< 4 years)--but not in long-term (> or = 4 years) users--than in never-users of OC. Non-significant estimates for RHs lower than 1.0, i.e. better prognosis, with long recency (> 5 years) and latency (> or = 10 years) of OC use were noted. Prognosis was not influenced by age at first OC use or of its timing in relation to the first pregnancy. A higher BMI was associated with a poorer prognosis, RH 5.9 (2.0-17.8) for BMI > or = 29 versus BMI < 19, but BMI was not a confounder or an effect modifier of the association between OC use and prognosis. This study does not indicate that OC use prior to the diagnosis of breast cancer has any adverse effect on the prognosis, at least not in women under 45 years of age at diagnosis.
Vasectomy has been accepted for family planning by approximately 42 million couples worldwide, the majority of whom live in developing countries. It is a highly reliable and safe contraceptive method, which has been extensively studied. Recently, however, renewed concerns have been raised about a possible effect between vasectomy and cancer of the prostate many years after the procedure has been performed. These concerns are based on research conducted in the USA, where there is a high and rising incidence of prostate cancer. This review discusses the evidence for this association and its potential impact in developing countries. The factors influencing the development and growth of prostate cancer are poorly understood and complicate any research into risk factors for the disease. Overall incidences of prostate cancer in some developed countries, such as the USA, are fifty times higher than in some developing countries, such as China. The majority of epidemiological studies on the relationship between vasectomy and prostate cancer have been based in the USA, but the findings are inconsistent and the reported associations weak. On the basis of currently available data, no changes in family planning policies with regard to vasectomy are warranted, but the concerns raised by these studies require that research into any possible association be undertaken in developing countries where vasectomy is widely practised.
The risk of pelvic inflammatory disease (PID) associated with use of an intrauterine device (IUD) has been an important concern that has dominated decisions on its use throughout the world, especially in the USA. Early research that suggested such an association led to both a dramatic decline in use of the method and its withdrawal from the US market by two manufacturers. However, factors other than use of an IUD are now thought to be major determinants of PID risk. To address these concerns, we have reviewed the World Health Organisation's IUD clinical trial data to explore the incidence and patterns of PID risk with use of an IUD. The overall rate of PID among 22,908 IUD insertions and during 51,399 woman-years of follow-up was 1.6 cases per 1000 woman-years of use. After adjustment for confounding factors, PID risk was more than six times higher during the 20 days after insertion than during later times (unadjusted rates, 9.7 vs 1.4 per 1000 woman-years, respectively); the risk was low and constant for up to eight years of follow-up. Rates varied according to geographical area (highest in Africa and lowest in China) and were inversely associated with age. PID rates were lower among women who had IUDs inserted more recently. Our findings indicate that PID among IUD users is most strongly related to the insertion process and to background risk of sexually transmissible disease. PID is an infrequent event beyond the first 20 days after insertion. Because of this increased risk with insertion, IUDs should be left in place up to their maximum lifespan and should not routinely be replaced earlier, provided there are no contraindications to continued use and the woman wishes to continue with the device.
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.
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.
Independent reports of legal abortions in two Swedish epidemiologic studies of breast cancer in young women, covering the same women and overlapping the same time period, have been compared in order to estimate a putative response bias. One study used case-control methods and obtained data by retrospective interviews from 317 cases and 512 controls. The other study was based on objectively documented information froma nationwide registry covering legally induced abortions. Analysis demonstrated a ratio between the odds ratios from the two studies of 1.5 (95 percent confidence interval 1.1-2.1) and an observed ratio of 22.4 (p less than 0.007) between underreporting of previous induced abortions among controls relative to overreporting among cases. This response bias may explain the tendency toward increased risk of breast cancer which, according to several case-control studies, appears to be associated with induced abortion.
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.
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.
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.
Antenatal care is an acknowledged measure for the reduction of maternal and perinatal mortality. In the rural village of Ilula, Tanzania, the possible impact of antenatal care on mortality was studied longitudinally on the basis of the 707 women delivered in the study period. Ninety-five percent of the antenatal records were available. Anemia, malaria and anticipated obstetric problems were the most frequent reasons for interventions. Among the women from the area who were delivered in hospital, 90% had been referred there. No relationship was found between the number of antenatal visits and the pregnancy outcome, but perinatal mortality was correlated to a low birth weight. Even with a mean attendance rate of six visits and full coverage by antenatal care maternal and perinatal mortality remains high.
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.
A prospective area-based study on the outcome of pregnancy was carried out in the rural village of Ilula in Tanzania. A coverage of 99% (n = 719) regarding the ultimate outcome for mother and child was achieved, including deliveries that took place in hospital (9%), at the dispensary (67%) and at home (23%). There were four maternal deaths (6/1,000). The mean birth weight for singletons was 3,070 g and the low birth weight (less than 2,500 g) rate 13%. From a gestational age of 37 weeks onwards there was a definite slowing of fetal growth. Perinatal mortality rate was 82 per 1,000 born, half of the deaths occurring in low birth weight babies. Twinning occurred in 3.5% and the mean length of gestation at delivery for these pregnancies was 35.5 weeks. Twins constituted 6.8% of newborns but accounted for 23.0% of perinatal losses, making twin pregnancy a major contributor to perinatal mortality. Post-term pregnancies carried no significant increase in mortality. It is concluded that reliable area-based data on the outcome of pregnancy in Tanzania can be obtained at village level, with good coverage of the study population, by properly instructed and motivated local staff with moderate supervisory support.
This is the first reported study of birth outcomes of a group of women whose own birth weights and gestational ages had been previously recorded. Births occurring from 1972 to 1983 among 1154 Swedish women, born from 1955 to 1965, were studied. Women who were themselves small for gestational age (SGA) at birth were at increased risk of giving birth to a SGA infant (odds ratio = 2.21, 95% confidence interval = 1.41, 3.48). Women who had been SGA had an even greater increase in risk of giving birth to a preterm infant (odds ratio = 2.96, 95% confidence interval = 1.47, 5.94). Women who were preterm at birth were not at increased risk of giving birth to either preterm (odds ratio = 0.65, 95% confidence interval = 0.15, 2.74) or SGA (odds ratio 1.21, 95% confidence interval = 0.62, 2.38) infants. It is concluded that the long-term effects of intrauterine growth retardation may extend to the next generation; women who had been SGA should be considered at increased risk to give birth to both growth-retarded and preterm infants.