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Protein A-Related Protein A (PAPP-A)

Alexey Portnov, medical expert
Last reviewed: 23.04.2024

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In normal pregnancy, the concentration of PAPP-A in the serum increases significantly from the 7th week. The increase in the concentration of PAPP-A occurs exponentially at the beginning of pregnancy, then slows down and continues until delivery.

trusted-source [1], [2], [3], [4], [5], [6]

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Obstetrician-gynecologist

The reasons for the decline in PAPP-A

With chromosomal abnormalities of the fetus, the content of PAPP-A in the serum in the I and early II trimester of pregnancy (8-14 weeks) is reduced in two thirds of women. The sharpest decrease in the concentration of this protein is noted in trisomy on the chromosomes 21, 18 and 13. Anomalies of sex chromosomes in the fetus are also often accompanied by a decrease in the content of PAPP-A in the serum of the pregnant woman. Changing the concentration of PAPP-A is also possible with trisomy on the chromosome 22. The predictive value of PAPP-A for the detection of fetal anomalies is higher than the change in levels of such well-known markers as AFP, CG, trophoblastic β ₁ -globulin, as well as unconjugated estriol and inhibin A, and is comparable to that for free β-CG. The decrease in the level of PAPP-A in chromosomal abnormalities of the fetus is most pronounced at the 10-11th week of pregnancy.

Median concentrations of serum PAPP-A for screening for congenital malformations

Pregnancy, ned	Median concentrations of PAPP-A, mg / L
8	1.86
9	3.07
10	5.56
Eleven	9.86
12	14.5
13	23.4
14	29.1

An even sharper decrease in the concentration of PAPP-A in the blood serum of a pregnant woman is observed when the fetus has Cornelia de Lange syndrome, in which, as in trisomies in autosomes, multiple dysplasias, malformations, delayed psychomotor and physical development are observed.

Another independent pathognomonic symptom of aneuploidy of the fetus at the end of the first trimester of pregnancy is a thickening of the occipital fold, which is revealed by ultrasound examination, however, visualization of this form of local edema of soft tissues is quite complex and subjective even with the use of modern scanner models with high resolution. It should be noted that early verification of fetal trisomies after ultrasonic or biochemical screening and subsequent karyotyping of cytotrophoblast, obtained with chorion biopsy, allows the termination of pregnancy in the first trimester. In the second trimester, fetal aneuploidy is verified by karyotyping fibroblast-like cells from the amniotic fluid.

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