You can't. At least with current tools. The field of genomics has 3 eras 1) read (sequencing), 2) edit (CRISPR, Zn-finger nucleases), 3) and write (long scale de novo synthesis). Right now, genomics is in the early phase of era 2 and molecular editing technologies still have a very long way to go before they are fully mature. On the 'writing' side for era 3, we have the ability to perform short read synthesis, and stitch those fragments together using Gibson assembly, there are size limits to this approach.
Bigger issues arise with simulating the complexity of the uterine microenvironment. A genome is a not an organism, and there are complex mechanical and chemical signals that contribute to the development of the fetus.
Synthesizing and modifying prokaryotes is much more feasible but we're still a ways off from doing this with any precision or at industrial scale.