Abstrak
<div><p>Implantation is the most critical stage in the establishment of pregnancy. In mammals, it has been estimated that between 25% and 60% of conceptuses are lost before or at the time of implantation. The objectives of this study were to investigate the ability of blastocyst hatching and attachment of trophoblast cells in <em>in vitro</em>, the outgrowth and differentiation of trophoblast cells in <em>in vitro</em> culture of hatched and non hatched blastocyst, the activity of mitochondria NADH-CoQ reductase and the pattern of mitochondrial distribution. Blastocysts were collected from mice cornua utery at day-4 of pregnancy and were divided into 3 groups: blastocysts undergo hatching within 24 hours, 48 hours and non hatching. Embryos were cultured in DMEM medium in 5% CO<sub>2</sub> incubator at 37°C for 10 days. The trophoblasts monolayer were processed for Giemsa staining and histochemistry analysis of NADH-tetrazolium reductase activity. The outgrowth of trophoblast cells were measured using eyespiece micrometer. The results showed the ability of blastocyst hatching in <em>in vitro</em> were different. The trophoblast outgrowth diameter of 24 h hatched blastocyst was significantly different with the 48 h hatched and non hatched blastocyst. The activity of NADH-CoQ reductase of 24 h and 48 h hatched blastocysts showed higher intensity than the non hatched blastocysts (P<0,05) and the distribution of mitochondrial in trophoblast cell cytoplasma of 24 h and 48 h hatched blastocyst were homogen around nucleus whereas thoes of non hatched blastocyst were cluster and heterogen. In conclusion, in <em>in vitro</em> study the failure of blastocysts hatching and implantation was due to the failure of outgrowth and differentiation of the trofoblast cells and the impairment of NADH-CoQ reductase activity in complex I mitochondria to produce energy and the pattern of mitochondrial distribution.</p><em>Key words</em>: mitochondrial distribution, NADH- tetrazolium reductase, trophoblast, implantation</div><div> </div>