This is indeed a fascinating discussion. Interferon sounds a very attractive option but I would like to put a word of caution on the use of pegylated IF during pregnancy as it may have a deleterious effect on the fetus.

She is young, the conception may be postponed until better situation.
She can come to planned pregnancy in much safe condition.
A deep MR can be shortly achieved on TKI2. Endometriosis may be treated in parallel using the drug schemes that suppress the level of estrogens (and simultaneously have the contraceptive effect).
In vitro fertilization may be accounted as she has a decreased chance of natural conception.

We have lost one woman with newly diagnosed CML and pregnancy on interferon, there was no hematologic response, imatinib was started at late terms but she progressed shortly after delivery.

It would be interesting to know an update of this patient's story.

I was surprised to see the poster on ASH 2015 where 10-12 women with ET and pregnancy were successfully treated by PEG-interferon.

I have now treated about 25-30 women with either CML or ET using interferon and in 6-8 cases Pegasys. In at lease 2 cases, women underwent fertility therapy while on interferon and Pegasys respectively. All pregnancies have apparently resulted in normal deliveries with no obvious fetal issues. I repeat my concern about patients not presenting pregnant and that is not switching them to interferon until they have a good and stable response to TKI, watching them for 6 months to be sure the response is sustained on the interferon, before telling them to go ahead and try to get pregnant. In only one case, has a patient lost response during the 6 month interferon observation period, and they went back on their TKI. Unfortunately, she had become pregnant "accidently" and when it was discovered that she had lost her molecular response, she elected to terminate the pregnancy. For women presenting while pregnant or becoming pregnant while on TKI, the scenario is different. With the former group, there is the risk of disease progression as described in one of the cases here. With the latter group, there may already be fetal issues and if the CML is not well controlled, disease issues before the end of term.
In regard to reducing the chances of conception, I only have one case where the woman also had polycystic ovary disease, where pregnancy was not successful. In fact in women with ET, about half my group, repeatedly spontaneous abortions were usually part of the history prior to starting interferon. I expect that the interferon controls the platelets, reducing the chance of thrombosis in vessels in the placenta, but also remembering that the placenta secretes interferons itself, something thought to be involved in fetal retention under normal circumstances. The use of exogenous interferon may just enhance this process.

I have a patient who was in the accelerated phase at the onset of TKI therapy but subsequently became molecularly well controlled on glivec to <0.1%. She became pregnant and we stopped the TKI . She couldn’t afford the interferon therapy and had disease progression by BCR_ABL RT-PCR to 17% . She really wanted the pregnancy. She has had to go back to the TKI. How have others managed similar patients?

I guess that I am fortunate to live in a system of socialized medicine where I can get coverage for the interferon so long as I have produced the necessary 5 km of paperwork. You do not specify when the recurrence happened during the pregnancy. There are individuals who believe that the TKI can be used during the third trimester and some even feel the second trimester. I must admit that I have a degree of discomfort with this, but it is an option. I cannot quote the risk if any, as the later stage of pregnancy develops. I have never had this situation. In a handful of cases where accidental pregnancy has occurred while on TKI, the patient has elected to terminate the pregnancy early and continue with the TKI. This is a case of AP CML an the risk of blast crisis is not trivial. I would favor termination of pregnancy if early and restarting TKI. If late in pregnancy, then add TKI and hope for no problems.