Radiotherapy is almost always contraindicated in pregnancy.
Radiotherapy can have multiple effects on the developing embryo and fetus.
Prior to implantation, radiotherapy causes an 'all or nothing' phenomenon - if the pregnancy is damaged sufficient there will be a spontaneous abortion; otherwise the pregnancy will likely continue as normal.
During gastrulation and organogenesis, radiotherapy may lead to congential malformation by inhibiting the development of various organ systems. For these reasons, radiotherapy in the 1st trimester is contraindicated.
If radiotherapy is indicated for treatment of malignancy in the first trimester, there are several options:
- Consider alternative treatment modalities (eg. mastectomy instead of wide local excision)
- Consider termination
The second trimester represents a very difficult time as termination is often difficult and radiotherapy is also contraindicated.
Radiotherapy in this phase does not cause malformation but can lead to reduced head circumference and mental retardation with doses as low as 0.5 Gy.
In this phase, radiotherapy should be avoided or delayed until delivery can occur in the third trimester; alternatively a late termination may be considered if there are no other alternatives.
The third trimester represents one of the easier times as delivery can usually be accomplished within 4-8 weeks of diagnosis. Delivery after 28 weeks is associated with excellent outcomes and delivery after 32 weeks is associated with outcomes equivalent to full term delivery (if managed in the appropriate hospital setting).