Each person has about 100 mutations (genetic defects) more than their parents. Allowing a generation time of 25 years the genetic load has increased by 10,000 defects over the last 2,500 years. The more genetic defects we carry the greater the chance that a conception will have a lethal combination that is not viable. Obviously if we are born we got a not lethal combination of defects, although many people have diseases related to genetics.
It is quite reasonable to believe that Adam and Eve were created with perfect genomes and would have had 100% successful pregnancies. Following the fall the corruption of the world would include genetic defects and the accumulating genetic load and high failure rate of conceptions today would be the result.