Because that's when the vital organs are shaped, heart, brain etc.
the organs grow larger
3rd trimester
blood flow from the mother to the fetus
the first trimester
they are passed to the fetus and cause imbalanced compounds that effect DNA
in the first trimester
At the third trimester.
It grows in size
in the first trimester/3 MONTHS
second trimester
Three Months.
more blood transfer to the fetus