First trimester pregnancy risk assessment of choromosomal abnormalities

It has become appearent from the results of several preliminary studies that sereening for choromosomal abnormalities in the first trimester is possible but that the parameters used must be different from those in the seconel trimester.
The most promosing parameters in the first trimester appear to be pregnaney associated plasma protein A (PAPP-A) and free [3-hCG as serum biochemical agents. Using PAPP-A alone, 60 % of Down syndrome cases would be identified, for a false positive rate of 5 %. Using free fi-hCG, instead of total hCG, in serum improves, 8 %-10 %, the deteetion rate of choromosomal abnormalities.
As a companion to the use of maternal serum analytes for predieting risk for choromosomal abnormalities, there are a characteristic set of ultrasound detectable anomalies that have been periodically found, which should heighten the suspicion when they are seen for the major aneuploidy conditions such as trisomies 21,18 and 13. Enlarged nuchal membrane (or transluceney) in the early first trimester weeks and may be important for the aneuploidy conditions.
Cerebral ventriculomegaly, holoprosencephaly, choroid plexus eysts, cranial posterior fossa eysts, nuchal eystic hygroma, nuchal edema, heart defects, hyperecogenic bowel, small for gestational ages are the ultrasnographic finclings in the late first trimester weeks. Although the odds of an aneuploid condition may be very high, none of the finclings on ultrasound are alone pathognomonic of any particular aneuploid condition.
A number of studies have looked at parameter as PAPP-A, free (3- hCG, nicked (3, urinary gonadotropin protein, SP 1, dimeric inhibin and ultrasound. This has resulted in a state of condition about the most likely best combination of parameters. By specifiying the demographic of the patient's age, ethnic background, maternal age a particular cocktail of parameters may be run.
And finally, Chorion Villus Sampling, as a known invasive technic, may be used for the detection of chromosomal abnormalities in high risk groups isolated by biochemical anaiytes and ultrasound examination.