It's most likely to occur if chemotherapy is taken during the first trimester, when the organs are forming. The brain and nervous system are still developing through the third trimester, however, and we don't know what impact, if any, we may be having on that. In addition, he said, chemotherapy given during the third trimester can suppress the development of white blood cells and blood platelets in the infant, placing the child at risk for infection and hemorrhage at birth. Abdominal surgery for a malignancy is also best done during the second trimester. By then, the pregnancy is well established and stable and the uterus is less irritable.
Radiation therapy is avoided whenever possible during pregnancy.
The rarity of cancer during pregnancy is responsible for the lack of solid information about how best to treat it. The large clinical studies required to learn the safest, most effective ways to diagnose, manage, and treat the condition are simply impractical to do. In the early 1980s, John Mulvihill, a pediatrician and geneticist then at the National Cancer Institute , grew concerned about this lack of information. There wasn't even a database available covering the information that was known, he said. So we built our own database.