The donor goes through tests to determine the dosage of hormones she will need to stimulate her ovaries to produce eggs.
The aim of the medication is to produce six to 16 follicles with an egg each, said gynaecologist Roland Chieng.
When these follicles mature, their eggs are retrieved.
The whole process before retrieval can take two to eight weeks, said DrChristopher Chong, also a gynaecologist.
Side effects of the hormone treatment can include abdominal swelling, mood swings and bruising at injection sites.
Less frequent, but serious, is ovarian hyperstimulation syndrome, which can be life-threatening. Patients require care and monitoring in hospital.
Eggs are retrieved through the vagina in a 20-minute procedure performed with the donor under local anaesthesia.
An ultrasound probe guides a tube attached to a suctioning needle into each ovary where the mature eggs, or oocytes, are removed from their follicles.
The donor can go home the same day.
Dr Chieng said the procedure was usually well tolerated and side effects were rare. They can include injury to the bladder, bowel, uterus or blood vessels. This happens in about one in 1,000 procedures.