The technique, discussed in a report published online May 14 in Human Reproduction, could also help fertility experts prevent accidental multiple pregnancies in their IVF patients.

A woman's eggs are fertilized with sperm during IVF and then allowed to develop in the laboratory for about five days until they reach the blastocyst, or very early embryo, stage. Doctors then decide which blastocysts look most likely to develop successfully and how many to put into the woman's womb.

Since reliable tests for determining which blastocysts are viable do not exist, couples often choose to have more than one blastocyst implanted in the woman's womb. While this increases the chances of a successful pregnancy, it also raises the risk of a woman becoming pregnant with two or more babies at once. Multiple pregnancies bring added dangers to the mother and babies.

In the study, researchers removed cells from the blastocysts being developed for 48 women, 25 of whom later became pregnant from the fertilized eggs resulting in 37 babies being born. The DNA from these cells was matched with the babies' DNA, thereby telling researchers which blastocysts developed into babies.

In analyzing the expression of genes in the viable and non-viable blastocysts, the team noted differing patterns. The genes expressed in the viable blastocysts, for example, are involved in cell adhesion, cell communication, cellular metabolic processes and response to stimuli -- all key processes involved in embryo implantation.

This finding could lead to doctors being able to select the single most viable embryo from a group for transfer from the laboratory to the womb, the researchers said.

"One of the major stumbling blocks to worldwide acceptance of a single embryo transfer policy is the lack of highly predictive criteria to select the single most viable embryo within a cohort," co-author Dr. Gayle Jones, senior research scientist at the Monash Immunology and Stem Cell Laboratories, said in a prepared statement. "The ability to use objective, measurable criteria rather than subjective observations, such as morphology, should improve the predictive value and provide sufficient confidence for clinicians to shift towards single embryo transfers for all patients without a concomitant drop in pregnancy rates. This would effectively reduce multiple pregnancies, which is a priority in the field of assisted reproductive medicine at present."

More work needs to be undertaken before these findings become applicable in the clinic, the researchers said.

More information

The American Society for Reproductive Medicine has more about infertility.

Giving Plavix (clopidogrel) did reduce the risk that a blood clot would block the vessel created by combining a vein and an artery, a standard procedure for kidney dialysis. But adding the clot-preventing drug did not increase the number of fistulas, as they are called, that could be used for artificial kidney treatment over the long run, the study authors reported.

The study was done because "early thrombosis [blood clotting] is one of the major causes of fistula failure," said Dr. Laura M. Dember, an associate professor of medicine at Boston University, and lead author of the report.

"What we found was that despite the reduction in thrombosis that was clear enough, there was an equal proportion of fistula failure," Dember said. "What is ultimately important is the usability of the fistula for dialysis."

The researchers published their findings in the May 14 issue of the Journal of the American Medical Association.

About 470,000 Americans have kidney failure and are kept alive by dialysis, in which their blood is run through a machine that filters out impurities. The preferred technique for linking to the artificial kidney is to create a fistula, which has lower rates of thrombosis -- blockage -- and infection than alternatives such as synthetic artery-vein grafts. But many fistulas never mature enough to allow dialysis.

The multi-center trial included 877 people with total or partial kidney failure who underwent surgery to create a fistula. Half were given Plavix for six weeks after the surgery, while the other half were not.

Plavix did reduce the risk of blockage by 37 percent over the six-week period. Among the 866 people who were tested, 12.2 percent of those given Plavix had a blockage, compared to 19.5 percent of those not given the anti-clotting drug.

But Plavix therapy did not reduce the incidence of cases in which the fistula could not be used for dialysis, which was 61.8 percent in those getting the drug and 59.5 percent in those getting a placebo.

The rate of fistula failure was about 50 percent higher than anticipated, Dember said, and that might have an effect on future practice.

"There has been an increased emphasis on trying to create fistulas in as many patients as possible," she said. "So, the criteria have changed. We need to develop better methods for selecting suitable candidates for fistula creation."

The trial also indicated the direction that that research should take, Dember said.

"Our future efforts should be directed at understanding the basic mechanisms of fistula maturation," she said. "If we better understand those mechanisms, we should be able to identify maturity-enhancing interventions."

More information

The basics of kidney dialysis are explained by the U.S. National Library of Medicine.

Positron emission tomography with a radioactive tracer (18F-FDG PET) is one of three imaging techniques commonly used to check whether head and neck squamous cell cancer has spread to the nearby lymph nodes in such patients. This is important in determining the prognosis of the disease, since some patients who clinically appear free of these types of metastases may actually have small tumors within their lymph nodes.

The findings are based on an analysis of 32 previously published studies done on head and neck cancer patients with one or fewer nodal metastases. The team from the University of Ioannina School of Medicine, in Greece, found that FDG-PET failed to identify half the lesions in patients whose lymph nodes tested negative.

The analysis, published online May 13 in the Journal of the National Cancer Institute, also found that the imaging technique incorrectly identified normal tissue as being cancerous 13 percent of the time.

The sensitivity and accuracy of FDG-PET compared with the two other common imaging techniques used -- magnetic resonance imaging (MRI) and computed tomography (CT) -- appears to be slightly better, but researchers said the differences were not statistically significant. The rate of false positives for each of the three imaging techniques was similar.

"Thus, there is little evidence to support the routine use of 18F-FDG-PET to evaluate possible lymph node metastasis among patients with [head and neck squamous cell cancer] and a clinically negative neck," the authors wrote.

An accompanying editorial in the journal notes that clinicians typically use multiple imaging techniques and clinical examinations rather than a single test to compose a full picture of their patients condition and disease.

"Prospective data remain a critical necessity to translate imaging improvements with FDG-PET into proven treatment improvements," the editorialists wrote.

More information

The U.S. National Cancer Institute has more about head and neck cancers.

But, the study authors noted, ultrasound also significantly increases the rate of false-positive readings.

"In our study participants, half of the breast cancers were found using mammography alone. By adding ultrasound, we found 78 percent of the cancers," said the study's lead author, Dr. Wendie Berg, a radiologist at an outpatient center in Lutherville, Md., affiliated with Johns Hopkins Medical Center.

However, identifying those extra cancers came with a cost of significantly more false-positive readings.

"With mammography, a woman has about a one in 40 chance that a biopsy will turn out not to be cancer. With the addition of ultrasound, it's one in 10," Berg said.

Results of the study, which was funded by the Avon Foundation and the U.S. National Cancer Institute, were published in the May 14 issue of the Journal of the American Medical Association.

Each year, more than 180,000 American women are diagnosed with breast cancer, and almost 41,000 will lose their lives to the disease. Death rates from breast cancer have been declining, possible due to earlier detection and diagnosis, according to the American Cancer Society.

The new study included almost 3,000 women recruited from 21 centers. The average age was 55 years old, and all of the women had a higher-than-normal risk of breast cancer.

The women were randomly assigned to receive either mammography alone or mammography plus ultrasound performed by a physician.

Forty women were diagnosed with breast cancer within a year of their initial screening. Mammography alone uncovered 20 cancers, 50 percent, while the combination screening technique found 31 of the cancers, or about 78 percent, according to the study.

That means for every woman screened, mammography alone will find 7.6 cancers, mammography plus ultrasound will detect 11.8 cancers, and three cancers will be missed altogether, the researchers said.

The study found that ultrasound was a good complementary screening tool for mammography, because it found cancers that mammography might miss.

"Ultrasound performs best in cases for which mammography performs weakest, i.e., in breast areas with dense fibroglandular tissue," Dr. Christiane Kuhl, with the Department of Radiology at the University of Bonn in Germany, wrote in an accompanying editorial in the journal. Kuhl also noted that the drawbacks to ultrasound include the frequency of false-positives, the cost of the test, and a lack of evidence that the test affects mortality.

Berg noted that there aren't currently enough physicians or ultrasound technicians trained for ultrasound to be a viable, widely used screening tool right now, even just for high-risk women.

"On average, physicians can only perform three to five ultrasounds per hour," said Berg, compared to as many as 50 mammograms in an hour, according to the editorial.

Dr. Julia Smith, director of the Lynne Cohen Breast Cancer Preventative Care Program at the New York University Cancer Institute and Bellevue Hospital in New York City, said, "I already do ultrasounds on women at risk. As a complementary test, ultrasound can be a very useful test. Also, we know it's relatively inexpensive and safe."

Magnetic resonance imaging (MRI) may be more effective than either mammography or ultrasound, and it's fast becoming a popular tool for breast cancer screening, but, Smith said, the cost of MRI is prohibitive.

Given limited health-care resources, Kuhl wrote that "mammography will probably remain the basis for breast cancer screening for the foreseeable future."

Smith said what's most important is for women to talk with their doctors about their individual risk of breast cancer, and then decide which screening tests would be most appropriate.

More information

To learn more about breast cancer screening options and current recommendations for screening, visit the American Cancer Society.

The bad news is a risk factor you can't change: Women whose sisters were diagnosed with breast cancer face an increased risk of breast cancer throughout their lives, regardless of their sister's age at diagnosis, according to a study in the May 13 issue of the Journal of the National Cancer Institute (JNCI).

The good news comes from a risk factor you can do something about: Women who exercise are much less likely to develop breast cancer, according to two new research studies -- one from the same issue of JNCI, and the other from the 2008 online first edition of the British Journal of Sports Medicine.

The first study from JNCI compared the rate of breast cancer in nearly 24,000 sisters of women with breast cancer to the rate of cancer in nearly 1.8 million women with sisters who didn't have breast cancer. All of the women were from Sweden, and the data collection for the study spanned from 1958 to 2001.

The researchers found that women between the ages of 20 and 39 who had a sister who'd been diagnosed with breast cancer faced a sixfold higher risk of breast cancer than did women whose sisters didn't have breast cancer. The excess risk declined as the women aged but didn't disappear. Women who were older than 50 with a sister with breast cancer had about a twofold risk of developing the disease, according to the study. And, it didn't matter what age the sister was when she was diagnosed.

"After the diagnosis of breast cancer in a family, the other sisters -- especially the youngest -- have an increased risk of breast cancer that persists for 20 years," said one of the study's authors, Marie Reilly, a professor of biostatistics at the Karolinska Institute in Stockholm, Sweden. "This suggests that sisters of breast cancer patients, especially the young sisters, should be intensely screened, independent of the screening recommendations for women their age."

Dr. Julia Smith, director of the Lynne Cohen Breast Cancer Preventative Care Program at the New York University Cancer Institute and Bellevue Hospital in New York City, called the findings "interesting and troubling." She added, "Sisters have to worry about increased risk no matter when their sister was diagnosed."

The second study from JNCI relied on data from the Nurse's Health Study II and included information from almost 65,000 women who completed questionnaires about their physical activity from age 12 until age 35. During the six-year follow-up period, 550 women from that group were diagnosed with breast cancer.

Women who walked about 13 hours a week or ran 3.25 hours a week had a 23 percent reduced risk of developing premenopausal breast cancer than women who were less active. The incidence rates of breast cancer were 194 per 100,000 "person-years" for the least active women, compared to 136 cases per 100,000 "person-years" for the most active women.

"These results suggest that consistent physical activity during a woman's lifetime is associated with decreased breast cancer risk. Unlike many risk factors for breast cancer, physical activity is an exposure that can be modified," wrote the study's authors, who were led by Dr. Graham Colditz, of Washington University School of Medicine in St. Louis.

Smith said: "For many reasons, women should continue to exercise and try to be in shape." It makes sense that exercise might reduce breast cancer risk, she said, adding, "Women who are exercising regularly are decreasing body fat and estrogen."

The third study on breast cancer risk was an analysis of 62 other studies that looked at the impact of physical activity and breast cancer risk. This review, published online ahead of the print version of the British Journal of Sports Medicine, found that women who are physically active have a 25 percent decreased risk of breast cancer.

The researchers found that both recreational or on-the-job activity could reduce risk, and that moderate and vigorous exercise caused a similar reduction in risk. This review also found that activity performed after menopause was more effective in reducing risk.

Smith recommends that women exercise at least 20 minutes, three times a week, and preferably more. She said that during those 20 minutes of moderate to vigorous exercise, the heart rate should consistently be above baseline.

More information

To learn more about breast cancer risk factors, visit the American Cancer Society.