RESUMEN
The rate of cellular proliferation and hypertrophy of the cardiac myocytes in the human perinatal period is still controversial. This work uses stereology to evaluate the prenatal quantitative changes of the myocardium. The hearts of 36 human foetuses, ranging from the 2nd trimester to the 3rd trimester, were studied. Fifteen random microscopic fields were analyzed in each heart. The following stereological parameters were determined: Vv[myocyte] and Vv[interstitium] (the volume densities of the cardiac myocyte and interstitium, respectively) and the Nv[myocyte] (the numerical density of the cardiac myocytes). The total number of myocytes (N[myocyte]) and the mean myocyte volume (V[myocyte]) were also determined. All differences between the second and the third trimester of gestation, tested with the Mann-Whitney test, were statistically significant (P < 0.05). The Vv[myocyte] decreased 8.69% and the Vv[interstitium] increased 49.83% in this period. Simultaneously, the Nv[myocyte] decreased 16.64%, the V[myocyte] increased 16.39%, the cardiac weight increased 366.67% and the N[myocyte] increased 272.06%. In conclusion, during the last two gestational trimesters the human heart increases in weight more than 4.5 times, the volume density of myocytes decreases while the volume density of the cardiac interstitium increases. The numerical density of myocytes per myocardium volume decreases but the myocytes became greater in mean volume (more than 16%).