It is a pregnancy with any complicating factors.
Maternal factors may be high blood pressure, high blood sugar, anaemia, increased age of more than 35 years, mode of conception like IVF (Test Tube baby), premature leaking, premature labor, maternal disease like heart or kidney disease.
Fetal factors may be growth restricted baby, congenital malformations, twin pregnancy.
A normal uncomplicated pregnancy can turn into a high risk pregnancy during any time in the 9 months of pregnancy, thus regular check up is mandatory to try to prevent and for early diagnosis of a high risk pregnancy.
The tiiming of delivery and mode of delivery differs from patient to patient.
It is always advisable to shift the mother to a proper setup with the baby inside the uterus where it is most safe, rather than deliver the baby and then shift the newborn.