Tinnitus: Causes, Symptoms, Diagnosis, and Treatments
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Pregnancy is a period of immense joy, anticipation, and, often, anxiety. One of the primary sources of this anxiety can be the health of the unborn child. Thankfully, modern medicine has provided us with a range of diagnostic tests to assess the health of the fetus. One such tool is the combined test.
The combined test is a prenatal screening tool that estimates the risk of the fetus having Down's Syndrome or Trisomy 18 (Edwards syndrome). It combines an ultrasound examination of nuchal translucency with a maternal blood test. The test does not provide a definitive diagnosis but expresses a probability of these conditions, which is then represented as a statistical percentage.
The result of the combined test is a number that represents a probability. If this number falls between 1/1 and 1/350, it is considered a high-risk result, warranting further investigation. However, it is important to remember that a high-risk result does not confirm that the child has Down's Syndrome or Trisomy 18. To confirm or rule out these conditions, an invasive test, such as amniocentesis or chorionic villus sampling, is required.
If the risk index is lower than 1/350, the probability is considered low. However, it is important to note that the presence of Down's Syndrome or other fetal malformations cannot be entirely ruled out. The combined test can statistically identify nine out of ten cases of Down's Syndrome, with the tenth case potentially escaping diagnosis.
The combined test is carried out in the 1st trimester of pregnancy (between the 11th and 13th weeks of gestation). It involves an ultrasound measurement of nuchal translucency and a dosage of two biochemical markers in the bloodstream, namely free-beta hCG (the free fraction of the β subunit of chorionic gonadotropin) and PAPP-A (pregnancy-associated plasma protein A).
The thickness of the nuchal translucency and the levels of these biochemical markers in the blood can indicate the risk of Down's Syndrome or other chromosomal pathologies. For instance, in cases of Down's Syndrome, the serum concentration of the β-hCG fraction is higher than in a pregnancy with a normal fetus, while PAPP-A is lower than normal.
The combined test does not pose any risk to the health of the mother or fetus. It involves a simple maternal blood sample, and the ultrasound measurement of nuchal translucency can be performed transabdominally or transvaginally. The ultrasound procedure can take up to 30-40 minutes, depending on the position of the fetus during the examination.
The risk of having a child with a chromosomal anomaly increases with advancing maternal age, becoming significant after the age of 35. However, it's important to note that the only way to definitively rule out a chromosomal anomaly is through invasive tests, such as chorionic villus sampling or amniocentesis, which carry a risk of miscarriage of approximately 1%.
Interestingly, around 70% of fetuses affected by Down's Syndrome are born to women under the age of 35. This is because younger women conceive more frequently than older women. However, in relative terms, older women give birth to a higher percentage of children affected by Down's Syndrome.
The combined test is suitable for all pregnant women under the age of 35 who wish to evaluate the risk of the fetus being affected by Down's Syndrome early on. It is also recommended for pregnant women over the age of 35 who wish to evaluate the risk more precisely before deciding whether to undergo more invasive prenatal diagnostic methods.
In conclusion, the combined test is a vital tool in prenatal screening. It provides a statistical risk assessment for chromosomal abnormalities, guiding the need for further, more invasive testing. With this information, expectant parents and their healthcare providers can make informed decisions about the course of the pregnancy and the care required.