Over the years, the sensitivity of commercially available pregnancy test kits has improved. Today, it is possible for a urine pregnancy test to confirm a pregnancy within a day of missing a period, which will be about two weeks after conception. Of course, there are still some tests which are not as sensitive and which will only be positive at significantly higher hormone levels. These higher levels may not be reached until ten to fourteen days after the date the period was due.
Unfortunately, yes, and again this depends on the type of test.
The pregnancy hormone detected in these tests is known as hCG. Some less specific test kits have the potential of cross-reacting with other naturally occurring hormones in the body, and this could lead to a false positive pregnancy test. Some infections may also lead to a false positive test, as may the use of some drugs, including penicillin and methadone.
Newer test kits are more specific and have greatly minimized the risk of a false positive pregnancy test.
It is possible, for a variety of reasons, for a pregnant woman to have a false negative test.
The most common cause of this error is the use of the older test kits with low sensitivity. Because they need high hormone levels to detect a pregnancy, a test performed too early may turn out negative and probably become positive a week later, when hormone levels are much higher.
The hormone hCG is produced in rapidly increasing quantities soon after implantation.
The blood concentration of the hormone doubles roughly every two days and reaches its peak at about nine weeks after conception (eleven weeks of gestation). It gradually falls thereafter to reach its nadir at about seventeen to eighteen weeks of gestation and remains at that level for the remainder of the pregnancy.
A faulty test kit may be one reason; wrong technique may be another and unfortunately, in some cases, a non-viable pregnancy may be the explanation. All in all, if a woman has a negative pregnancy test where she feels sure she is pregnant, she should seek prompt medical attention.
In most cases, an ultrasound scan will sort the uncertainty out.
Historically, the figures quoted are 5 per cent false positive and a substantially higher 15-20 per cent false negative. These figures are certainly no longer valid, as the tests have become more refined and false positives and negatives are much rarer now.
How soon does the baby start "kicking"?
As mentioned earlier, basic organ formation is complete by eight weeks of gestation.
In fact, fetal blood circulation is established three to four weeks post-conception.
Movement is detectable on the ultrasound scan even before eight weeks are complete. However, the fetus is still quite small (just over 2 cm long, at eight weeks) and the expectant mother should not expect to feel any movements for several weeks yet.
When does the mother start being aware of the fetal movements?
Some women may want to believe otherwise but it is extremely unusual for movements to be felt before sixteen weeks of gestation. In fact, in a first pregnancy, this may not take place until well into the eighteen to twenty weeks period.
Some women experience a sensation which is remarkably similar to fetal movements much earlier than sixteen weeks. In reality, this is caused by momentary spasms of muscles and even bowels, and is not a result of fetal activity.