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Although 30 years of research have pointed to a link between birth control pill use and the risk of stroke, the association is "tenuous at best and perhaps nonexistent," according to a meta-analysis including 36 studies.1 Overall, the pooled data showed that pill users had nearly twice nonusers’ stroke risk (odds ratio, 1.9). The association was significant in case-control studies (2.1), for stroke caused by blood clots (2.7) and for current pill users (2.0). However, the data suggest a negative association in cohort studies, show no association for stroke caused by bleeding in the brain or for stroke-related deaths, and indicate no elevation in risk for ever-users. Increases in risk were similar regardless of estrogen dose (1.8 for high- and low-dose pills) or type of progestin (2.4-2.9). Women’s risk factors were key to the relationship: Increases in risk were more marked for pill users who were 35 or older (2.3), smoked (3.5) or had high blood pressure (9.8) than for users without these risk factors (1.3-2.1). The analysts contend that the inconsistencies in the data, the low absolute values of the odds ratios and "severe methodological limitations" (which they outline in their report) cast doubt on the association between pill use and stroke risk, particularly in young women who do not smoke or have high blood pressure.

1. Chan W-S et al., Risk of stroke in women exposed to low-dose oral contraceptives: a critical evaluation of the evidence, Archives of Internal Medicine, 2004, 164(7):741-747.


In June 1999, the world population reached six billion—3.5 times its size at the beginning of the 20th century and twice its size in 1960—according to a report from the Census Bureau.1 The climb from five billion to six billion took a mere 12 years; by comparison, it took 118 years for the population to inch its way from one billion to two billion and 37 years for the next billion to be added. In 2002, the annual rate of population growth was 1.2%, the equivalent of 200,000 people a day, or 74 million a year; at that rate, roughly the number of people living in western Europe in 2002 will be added to the world population over five years. Dramatic as all of this may sound, growth is slowing: The number of people added in one year peaked at 87 million in 1989-1990, and the annual growth rate was 2.2% in the early 1960s. Analysts attribute the slowdown to fertility declines: Worldwide, women in 1990 had a lifetime average of 3.3 children; the figure was 2.6 in 2002 and is likely to drop below replacement level by 2050. The Census report takes a detailed look at these and other population-related trends and their projected impacts for the first half of this century.

1. U.S. Census Bureau, Global population at a glance: 2002 and beyond, International Brief, Washington, DC: U.S. Census Bureau, 2004.


Four years after students in 10 North Carolina public schools participated in a program to reduce dating violence, they were significantly less likely than their peers who had not received the intervention to report involvement in such violence.1 The Safe Dates program included a theatrical production staged by students, 10 educational sessions and a poster contest, and was implemented among eighth graders in five randomly selected schools in 1994-1995. Three years later, half of participants received a booster—a mailed newsletter and worksheets, followed by a phone call from a health educator—to reinforce the program’s messages. According to the teenagers’ own reports four years after the intervention, Safe Date participants had perpetrated significantly less physical, serious physical and sexual abuse within a dating relationship than students whose schools had not provided the program (betas, -0.1 to -1.1); they also were less likely to have been victims of sexual or serious physical violence (-0.2 and -0.5, respectively). Program effects were the same for white and nonwhite teenagers, and for males and females, but they varied somewhat by whether adolescents had previously experienced dating violence. However, students who received the booster did not report better outcomes than those who received only the original intervention.

1. Foshee VA et al., Assessing the long-term effects of the Safe Dates program and a booster in preventing and reducing adolescent dating violence victimization and perpetration, American Journal of Public Health, 2004, 94(4): 619-624.


Fourteen percent of participants in the National Longitudinal Study of Adolescent Health who had taken a virginity pledge had a nonmarital birth; the proportion was twice as high among their counterparts who had not taken a pledge.1 In an analysis by the Heritage Foundation, the difference could not be attributed to teenagers’ family structure or income, religiosity, self-esteem, school performance or race. When these factors were controlled for, pledgers had 40% lower odds of giving birth out of wedlock than nonpledgers. According to the analysts, the findings "strongly suggest" the potential of abstinence education programs to positively affect young people’s behaviors and life outcomes.

1. Johnson KA and Rector R, Adolescents who take virginity pledges have lower rates of out-of-wedlock births, Washington, DC: The Heritage Foundation, 2004.


Black and Asian women who gave birth in a London health region in 1988-1998 delivered earlier than their white counterparts, but their infants appeared to be further along in development, according to an analysis of data from a large maternity database.1 Half of black and Asian women gave birth within 39 weeks, whereas the median for whites was 40 completed weeks of gestation; 8% of deliveries among black women, 7% among Asians and 5% among whites were preterm. In adjusted analyses, normal-weight black women had significantly higher odds than whites of delivering preterm (odds ratio, 1.3); the odds were also elevated for Asian women, particularly if they smoked and were single and unsupported (1.5-2.3). In addition, the odds of an infant’s passing meconium, an indicator of fetal maturity, were elevated both for babies born to black women (1.5-1.6, depending on whether the delivery occurred before or at term) and for those born to Asians (1.5 if the birth was preterm). The analysts comment that "it may be appropriate to utilize different definitions of term" for different ethnic groups. Doing so, they note, "could potentially modify principles of obstetric practice."

1. Patel RR et al., Does gestation vary by ethnic group? a London-based study of over 122,000 pregnancies with spontaneous onset of labour, International Journal of Epidemiology, 2004, 33(1):107-113.


Three centuries of birth records in the southern part of the Netherlands indicate that conceptions (and, one may infer, heterosexual intercourse) occur most often in the spring; but a study of nearly a million Pap smears taken between 1983 and 1998 shows that women in this region are about twice as likely to contract human papillomavirus infection in August as in winter.1 Evidence of infection fell off abruptly every September. Meteorological data confirmed that in each year of the study period, the amount of sunlight available peaked in August. The researcher speculates that the increased incidence of infection during the summer is linked to the immune-suppressing effects of ultraviolet light. He emphasizes that it is important to confirm this relationship, "because whatever risk is conferred by sunlight is, in principle, behaviorally avoidable."

1. American Association for Cancer Research, Increasing the risk of cancer: new research sheds surprising results on potential sources of cancer risk, news release, Philadelphia: American Association for Cancer Research, Mar. 30, 2004.


The fortification of cereal grain products with folic acid, which the U.S. government has required since 1998 as a measure to prevent neural tube defects, appears to be having some impact.1 An analysis of data from a population-based surveillance system indicates that in 1999 and 2000, the annual number of pregnancies in which a neural tube defect (a serious malformation of the spine or brain) was diagnosed prenatally was 27% lower than it had been in 1995- 1996; similarly, the annual number of infants born with such defects was 26% lower than it had been in the earlier period. Women’s adequate consumption of folic acid can prevent more than half of these defects. Thus, while praising "the partial success of the U.S. folic acid fortification program as a public health strategy," the analysts stress that to further reduce the occurrence of neural tube defects, "all women capable of becoming pregnant" should follow the federal recommendation to consume 400 mcg of folic acid daily.

1. Mersereau P et al., Spina bifida and anencephaly before and after folic acid mandate—United States, 1995-1996 and 1999-2000, Morbidity and Mortality Weekly Report, 2004, 53(17):362- 365.


More than 170,000 Americans contract hepatitis A or B infection each year, but many people know little about these infections.1 One-quarter of hepatitis A infections are attributable to household or sexual contact, and half of hepatitis B infections result from contact with bodily fluids during sex. Yet in an online survey conducted early in 2004, substantial proportions of 18-35-year-olds did not know that hepatitis A and hepatitis B are sexually transmissible—57% and 44%, respectively. Nor is it universally known that safe, effective vaccines are available that can prevent these infections: Fifty-five percent of respondents were aware of this for hepatitis A, and 42% for hepatitis B. Six in 10 had not been vaccinated or were unsure as to their vaccination status; nine in 10 said that no health care provider had recommended that they be vaccinated, even though two in three had risk factors for infection. The head of the American Social Health Association, which sponsored the survey, comments that "people’s lack of awareness about the various STDs only underscores the need for continued education to prevent the spread of these serious diseases."

1. American Social Health Association (ASHA), Survey suggests lack of awareness heightens risk for sexually transmitted diseases, news release, Apr. 6, 2004, , accessed Apr. 7, 2004; and ASHA, Hepatitis A & hepatitis B: the only vaccine-preventable STDs, fact sheet on survey findings, , accessed May 12, 2004.


Advertising for home pregnancy tests claims that they are at least 99% accurate when used on the first day of a missed period, but an evaluation of 18 brands yielded considerably worse results.1 Following the instructions in the package insert, researchers tested each brand six times with five concentrations of human chorionic gonadotropin (hCG), the hormone produced by the placenta that is an early indicator of pregnancy. At an hCG level at which 95% of pregnancies should be detectable, none of the tests, when read at the suggested time (after 1-5 minutes), clearly indicated presence of the hormone; even at the highest hCG concentration tested, only 44% produced an indisputably positive result. The tests did better when they were read after 10 minutes and when questionable results were included, but only at the extended reading time did all 18 brands at least faintly detect the highest hCG level. Two brands gave false-positive results at the suggested reading time. The researchers suggest that "in fairness to the consumer," manufacturers of these products reassess their accuracy claims.

1. Cole LA et al., Accuracy of home pregnancy tests at the time of missed menses, American Journal of Obstetrics and Gynecology, 2004, 190(1):100-105.