The diagnosis of a post-term pregnancy is established on the basis of anamnesis data (medical history) and a combination of examination results:
• identification of factors that put a pregnant woman at risk (ovarian dysfunction, genital diseases, abortions and spontaneous miscarriages);
• correct calculation of the date of delivery, ultrasound in the first trimester of pregnancy;
• ultrasonic fetometry (measurement of the fetus) - the absence of an increase in the fetus when viewed in dynamics, the detection of growth retardation syndrome (symmetrical or asymmetric reduction in the circumference of the head and abdomen of the fetus);
• assessment of the volume and structure of amniotic fluid - the appearance of a suspension due to the presence of cheese-like lubricant, vellus hair, epidermis and meconium, a decrease in the volume of amniotic fluid (the smaller their volume, the higher the risk of true pregnancy overshoot);
• ultrasound assessment of the maturity of the placenta: a decrease in its thickness, reverse development of the placenta with a complex of its structural changes (calcifications, cysts);
• cardiotocography (CTG) - with fetal hypoxia, there is a change in fetal mobility (from increased to complete immobility), a change in the number of heartbeats, a decrease in the compensatory capabilities of the fetus during exercise;
• dopplerometry in the uterine arteries and umbilical cord arteries - a violation of blood flow of varying severity is recorded;
• assessment of fetal hemodynamics - blood flow velocity in the middle cerebral artery, aorta, venous duct and inferior vena cava of the fetus is reduced (indicates the degree of centralization of blood flow in the fetus);
• evaluation of the maturity of the cervix;
• amnioscopy - examination of the lower pole of the fetal bladder using an amnioscope (there is a decrease in transparency and a change in the color of the amniotic fluid).
The final diagnosis is established after the birth and examination of the child and the placenta. In histopathological examination of the placenta, fatty involution is observed (replacement of biologically active tissue with non-functioning adipose tissue), calcifications and yellow-green staining of the membranes.
Differential diagnosis:
• delayed delivery of a fetus without signs of overmaturity - characterized by a delay in the onset of labor, the absence of pathology according to the results of ultrasound and CTG, the birth of a child without signs of postmaturity, the absence of characteristic changes in the placenta according to the results of histology.
• timely birth of a child with signs of overmaturity - may be associated with the peculiarities of the maturation of the placenta and the body of the pregnant woman;
• the birth of a large fetus with gestational diabetes mellitus - the newborn has no signs of postmaturity.