Chromosomal testing can be done in two ways. Upto 16 wks non invasive methods are employed. If there is any abnormal findings invasive methods like amniocentesis may be offered. Fluid from the uterus  is drawn out and a cytology is done for abnormal cells. If there is a chromosomal defect the pregnancy must be terminated.

Most pregnancies are ridden with complications. And  a relatively safe procedure [ caesarean sections ] has increased the cases of caesarean sections.
High risk pregnancies, Test tube babies, Large healthy babies all lead to an increased incidence of  this operative procedure.

Yes it is possible. But  a vaginal trial is risky and has to be the obstetrician's discretion.

Every surgical interference is risky and increases the chances of more complications in the next pregnancy. Hence  two or three should be considered the limit. But again its the obstetrician who decides.

Pregnancy is not contraindicated ,but the mother should be counselled and the chances of having a HIV positive baby is to be explained. ART [Anti Retroviral Therapy ] should be started as quickly as posibble. Breast feeding is contraindicated in  HIV positive mothers.