An overview of new pregnancy screening tips

An overview of new pregnancy screening tips


A) Tips for screening protocols using mother serum

Patho syndrome increases Inhibin A in the second trimester screening.

- Of the side effects of the first trimester screening protocol to detect high cases of triploidy (either in the form of a digynic form - an extra chromosomal set of maternal origin - or in the form of a diandric form - an extra set of chromosomes of paternal origin) Is.

- In the triple genetic dii form: both PAPP-A and free BhCG ​​are severely reduced.

In tripled diandric form: free BhCG ​​is greatly increased, but PAPP-A does not change much.

There is no significant difference between the NT level in the above group and the control group in pregnancy following ART (either IVF or ICSI method). PAPP-A levels are slightly reduced in this group but are not significant. But the free BhCG ​​level increases significantly relative to the control group (about 13%).

- For the above reasons, the false positive rate of the first trimester screening protocol in pregnancies following ART is about 1% higher than in the group with normal pregnancies.

- During the time allowed for fetal screening protocols, the test detection power in a person changes ‌ (due to the range of changes in blood markers in different weeks), so if a screening protocol is repeated according to Fetal screening tests in the best screening centers in Tehran in two different time periods It is better to always be the worst risk assessment criterion.

- The level of Free BhCG ​​hormone in female fetuses with Down syndrome is up to 20.8%, the level of PAPP-A hormone in normal female fetuses is 10% and in fetuses with Down syndrome is 13% higher than male fetuses. Conversely, NT levels in normal female fetuses with Down's syndrome are about 3-4% lower than in male fetuses (this figure is up to 12% in some sources).

 This results in a 1-2% reduction in the detection power as well as a reduction in the number of positive screening tests for the first trimester in female fetuses compared to male fetuses.

- In Turner syndrome, NT increases significantly and PAPP-A decreases. But the free BhCG ​​level does not change significantly. 96% of cases of Turner syndrome in first trimester screening are detectable.

- In other sex-dependent chromosomal disorders such as supersynthesis (‌ 47, XXX‌), Kleinfelter (‌ 47, XXY‌ and its rare subtypes such as ‌ 48, XXXY‌ (which is the syndrome) ‌ Also called Barr-Shaver-Carr), ‌ 48, XXYY‌ and ‌ 49, XXXXY‌) and Jacob's syndrome or male cloud syndrome (‌ 47, XYY‌) only increase NT While the levels of the two free biochemical markers BhCG ​​and PAPP-A do not change significantly.

 Overall, 62% of other sex chromosome-related disorders are detectable in the first trimester screening.

B) Tips for NIPT testing

In general, cfDNA is a bp 150‌ piece of double-stranded DNA that is released from nucleosomes during apoptosis and necrosis.

- Some anticoagulant compounds (such as Enoxaparin, Aspirin, or Heparin) reduce Fetal Fraction by reducing the level of NPT testing (No result). Although the mechanism of action is unclear, because the apoptosis process plays a role in scaling the placental cells into the mother's blood, anticoagulant compounds reduce the apoptosis process by reducing the placental thrombosis process, reducing hypoxia, and reducing placental inflammation. .

- When we suspect an X-linked recessive disease in a family, because the probability of having a healthy girl is 50% and the carrier girl (like a mother) is 50%, and on the other hand, if the fetus is a boy, The disease can occur in him (there is a 50% chance of a sick boy and a 50% healthy boy), we can do NIPT (which has a high diagnostic power to determine sex) before any invasive test to determine the sex of the fetus. Let's use.

- According to studies conducted until 2018, adding a review of disorders related to sex chromosomes causes a doubling of positive screening cases (2.3% vs. 1.2%) and a decrease in OAPR (63% vs. 85%). %).

- In a large study conducted in 2017 by Dr. Samura et al. In Japan, the positive NIPT screen size was 1.8% and the PPV rate for trisomy 21 was 96.5%, and for trisomy 18 it was 82.8%. In Trisomy 13, 63.6% were reported, and two false negatives were reported.

 Thus, the diagnostic power of trisomy 21 was reported to be 99.3% (because 279 of the 281 cases of Down syndrome were diagnosed). Out of a total of 30,613 cases, no results were obtained for 51 patients tested for NPT (No result).

- The effectiveness of NIPT testing when the fetal age is high (ie in the late gestation stage, which is equivalent to 23 weeks or more of fetal age) and the patient has an abnormal ultrasound finding that greatly affects the physician and the patient. Worried very high (PPV is 100%).

- Failure to answer the NIPT test The lowest prevalence in MPS (Massive Parallel Sequencing) by 1.58% and the highest prevalence in SNP (Single-Nucleotide Polymorphism) 6.39%.. Is observed.

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