The study described in this volume is a result of a collaboration between two medical institutions in Toronto: the Princess Margaret Hospital and The Motherisk Program at The Hospital for Sick Children.

Princess Margaret Hospital (PMH) is an oncologic hospital in Toronto serving the province of Ontario. PMH maintains a computerized database of patients' records dating back to 1958, which was used to identify for the study all female patients who had cancer and pregnancy in their diagnosis from 1958 to 1987.

Based on the assumption that cancer would be present for some time before it could be diagnosed, the time frame for inclusion for this analysis selected women who were pregnant within nine months prior or three months after first treatment of their cancer. Nine months were chosen to reflect the normal gestational period and three months to arbitrarily create a time frame of one year (Fig. 6.1).

Since the date of diagnosis was often not recorded in the PMH database, we used the date of first treatment as a reference date, assuming that there would be a minimal delay from the time of diagnosis to treatment (surgical, radiological and/or medical). Extreme cases included in our study were therefore women who delivered nine months before their first treatment and women who conceived three months after the last day of their first treatment.

Potential cases identified by the computer were screened further by examining their charts to confirm that pregnancy and cancer occurred according to the time frame defined above, and to reject any patients who had an ectopic pregnancy.