pickles16
Real Estate Professional
Member since 11/07 17227 total posts
Name:
Jen
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Great Articles on HPT tests and implantation!!!!
Commercially available pregnancy tests kits may not be accurate on the first day or so after a missed period because of natural variability in ovulation and when developing embryos attach themselves to the lining of the wombs.
Attachment occurs roughly nine days after fertilization, but ranges from six to 12 days, Wilcox said. Pregnancy cannot be detected before implantation.
"The interesting thing we were able to look at was how the time of implantation varies among women in relation to their expected menstrual period," he said. "While on average, most people will implant before their expected menstrual cycle, the natural variability is something that doctors and pregnancy kit manufacturers haven't taken into account."
Ten percent of pregnancies in an original group of 221 women were undetectable that day even when an especially sensitive method was used to detect the telltale human chorionic gonadotropin hormone, researchers say. Pregnancy test kits from drugstores are reasonably reliable, but they are not as precise as the test employed by the North Carolina scientists.
"Our subjects were healthy women who were planning to get pregnant," said Dr Allen J Wilcox, senior investigator at the National Institute of Environmental Health Sciences and a University of North Carolina at Chapel Hill faculty member. "By analyzing daily urine specimens while they were trying to get pregnant and throughout the earliest part of pregnancy, we were able to pinpoint the day of implantation, which is the day the fertilized egg attaches itself to the lining of the mother's uterus."
The new study shows clearly that 10 percent of the embryo attachments -- and hence new pregnancies -- had not occurred by the day women expected their periods to begin, the physician said.
"These findings mean is that if women were to buy a test kit, follow the directions and test themselves on the first day of their expected periods, the test would be negative for many women, and they would not know that they’d become pregnant," Wilcox said. "This is true even if their doctors had given them a blood test for pregnancy that day."
If women waited for another week, the 10 percent of false negatives would decline to three percent or less, he said. A report on the findings appeared in the October 10, 2001 issue of the Journal of the American Medical Association.
"The message is that women who test themselves could be misled into thinking they’re not pregnant because the package inserts imply pretty strongly that if the tests are negative, then pregnancy has not occurred," Wilcox said. "In fact, there is at least a small chance that they are pregnant, but the pregnancy hasn’t got to the point yet where it is detectable."
The new findings are helpful, he said, because so many women buy the pregnancy test kits. In 1999, they bought about 19 million over-the-counter kits in the United States alone. US sales totaled about $230 million, and inserts typically instruct women to test as early as the first day of a missed period.
"Unfounded assurance that a woman is not pregnant could have important consequences," Wilcox said. "For example, women with a negative test result may fail to protect themselves from exposures to toxicants in the workplace or to medications that could damage a developing embryo. Many women will test positive a week or more before their period is expected, while a few women will test positive only a week or more afterward."
Young women and teens are frequent users of test kits but might be especially prone to false-negative test results because they are more likely to ovulate late.
Subjects, who ranged in age from 21 to 42, were recruited in central North Carolina between 1982 and 1986. Of the original group, 151 were pregnant for at least six weeks, and all had kept menstrual diaries and froze urine samples daily. Of those, 136 provided information about their usual cycle length and formed the final study group.
Wilcox and colleagues analyzed the samples for human chorionic gonadotropin, a hormone that increases rapidly following implantation, with an extremely sensitive immunoradiometric assay. That assay is more than 100 times more sensitive than most commercial pregnancy test products.
On the other hand...New study establishes when pregnancy starts
quote:
By DAVID WILLIAMSON
UNC-CH News Services
CHAPEL HILL – With help from healthy women trying to conceive babies, North Carolina scientists have uncovered the most precise information yet about when pregnancy starts in humans.
Fertilized eggs attach themselves to the lining of the womb six to 12 days after ovulation, the research shows. In most successful pregnancies, that implantation -- the real start of pregnancy -- occurs on day eight, nine or 10 following ovulation. Day eight appears to be the most successful.
The later the attachment takes place, the more likely a pregnancy will end on its own, the scientists found.
Conceivably -- no pun intended – as a natural protective mechanism, the uterus tends to reject fertilized eggs that take too long to adhere to the lining because they may be less fit, the researchers say. On day 11, more than 50 percent of pregnancies fail and on day 12, that number jumps to over 80 percent.
A report on the findings appears in Thursday’s issue (June 10) of the New England Journal of Medicine. Lead author is Dr. Allen J. Wilcox, chief of the National Institute of Environmental Health Sciences’ epidemiology branch and adjunct professor of epidemiology at the University of North Carolina at Chapel Hill School of Public Health. Co-authors are Drs. Donna Day Baird and Clarice Weinberg, both also of NIEHS and UNC-CH.
"This is a very basic piece of reproductive biology that will probably find its way into the textbooks," Wilcox said. "It’s a step forward in terms of what we understand about pregnancy. Eventually, it could have an impact on patient care, but it is not going to change the way physicians treat their patients immediately."
Researchers collected daily urine samples for up to six months from 221 healthy N.C. women attempting to conceive after stopping contraception, he said. Of 199 conceptions, enough information was available on 189 for analysis.
Of those 189 pregnancies, 141 lasted at least six weeks past the last menstrual cycle, and the other 48 ended in early loss, the scientist said. Among pregnancies lasting six weeks or more, the first detectable rise in the level of a hormone known as chorionic gonadotropin (hCG) -- an indicator of successful attachment of a fertilized egg to the uterus wall -- occurred six to 12 days after ovulation.
"The risk of early loss was strongly related to the time of implantation," the authors wrote. "Early loss was least likely when implantation occurred by the ninth day (13 early losses among 102 pregnancies, or 13 percent) rising to 26 percent (14 of 53 pregnancies) when implantation occurred on the 10th day, 52 percent (12 of 23) on the 11th day and 82 percent (9 of 11) with implantation after day 11."
Three pregnancies in which the first rise in hormone occurred after day 12 ended by themselves.
"This study was first intended to identify the proportion of pregnancies that were lost very early before women knew they were pregnant," Wilcox said. "But we also were able to look at the date on which pregnancy could first be detected in relation to ovulation.
"The first detection of pregnancy is really the first detection of hCG, which rises very rapidly once the fertilized egg attaches to the uterus. That’s in fact the most hidden event of pregnancy and has never been seen before."
Fertilization begins about a week earlier when egg and sperm unite, he said. Many fertilized eggs, however, never succeed in clinging to the uterine wall where they can grow into an embryo, fetus and, eventually, a baby.
"This is the first really concrete information we have about when pregnancy starts in humans – how long after fertilization does pregnancy begin," Wilcox said. "It probably has implications for assisted reproduction -- the way medicine is able to manipulate reproductive processes to encourage pregnancy – possibly by increasing the narrow implantation ‘window.’ We may want to be careful doing this though. We don’t want to shut down a mother’s natural ability to screen out some potential pregnancies that might not be doing well due to chromosomal abnormalities or other developmental problems."
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