Pregnancy Associated Protein A in the blood (PAPP-A)

Pregnancy-associated plasma protein A (PAPP-A) was discovered in the blood serum of pregnant women in 1974. The protein has a molecular weight of 820,000, a tetrameric structure, a developed carbohydrate component, and a pronounced affinity for heparin. The PAPP-A molecule has a structure identical to α ₂ -macroglobulin, which is an inhibitor of virtually all known proteinases.

During pregnancy, as well as in some malignant and inflammatory diseases, there is an increase in the biosynthesis of PAPP-A, which is manifested by an increase in its concentration in the blood serum. During pregnancy, the PAPP-A content in the blood increases thousands of times and before childbirth can exceed 200 μg / ml. The concentration of PAPP-A in the blood serum of primiparous women and women with a history of three or more pregnancies is reduced. Quite often, with a high concentration of PAPP-A, the mass of the placenta is also increased. Multiple pregnancy, as a rule, is accompanied by a high content of PAPP-A in the blood serum. After childbirth, a rapid decrease in the PAPP-A level is observed during the first 2-3 days, and then its concentration decreases on average by 2 times every 3-4 days.

In threatened miscarriage accompanied by bleeding (8-14 weeks of pregnancy) and the development of intrauterine hematomas, the volume of which does not exceed 15 ml, the concentration of PAPP-A in the blood does not change significantly. In women with bleeding in the 7-20th week of pregnancy, a low concentration of PAPP-A in the blood is detected more often than in a normal pregnancy. In addition, approximately 10% of women whose pregnancy ended in miscarriage had elevated concentrations of PAPP-A in the blood serum.

Almost all women with low placentation experience a less pronounced increase in PAPP-A concentrations in the blood throughout pregnancy.

In women with a normally located placenta, premature birth and fetal hypotrophy are most often observed in cases where there is a low level of PAPP-A in the blood serum at 7-13 weeks of pregnancy.

At the end of pregnancy, the concentration of PAPP-A in the blood serum, as well as its total content in the placenta in women suffering from diabetes mellitus, is significantly lower than in normal pregnancy. A decrease in these indicators before childbirth was also recorded in pregnant women with a history of arterial hypertension.

An increase in the PAPP-A concentration in the blood serum at 34 weeks of pregnancy is detected in women with severe forms of late gestosis, which often precedes the clinical manifestations of preeclampsia, and is also possible with increased diastolic pressure. Often, a high content of PAPP-A in the blood at 34 weeks is detected in those pregnant women who subsequently give birth prematurely or the postpartum period is complicated by bleeding.

Changes in the concentration of PAPP-A in the blood serum in pathological variants of the course of pregnancy

Type of pathology	PAPP-A
Miscarriage	↓ (I-II)
Fetal hypotrophy	↓ (I)
Fetal trisomy	↓ (I)
Diabetes mellitus	↓ (III)
Chronic hypertension	↓ (III)
Preeclampsia	↑ (III)
Premature birth	↓ (I); (III)
Postpartum hemorrhage	↑ (III)
Primary low placentation:
No complications	↑ (I-III)
Fetal anomalies	↓ (I); ↑ (II,III)
Fetal hypotrophy	↓ (I); ↑ (II-III);
Late miscarriage	↑ (I); ↓ (II);
Premature birth	↑ (III)

Note: ↑ - increase, ↓ - decrease. The trimester of pregnancy is indicated in brackets.

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