If the mother can't breathe properly, the baby can't get enough oxygen.
Worst case an untreated asthma attack could kill you.
My Pulmonary Dr told me that the mother's well being (and appropriate medication) are always considered of key importance and priority during pregnancy when it comes to asthma.
My OBGYN told me to keep taking my inhalers normally it shouldn't affect the baby in any way because it goes into your lungs not the babies...also he said when my uterus starts to grow my lungs will be squished by the rest of my insides and I will really need the inhalers then and he was right...
I am 22wks and I have come down with a severe chest infection which had meant I am on antibiotics and also a ventolin pump. The only time my asthma seems to play up is when I am ill.
My advice would be speak to your midwife/ob/doctor and get advice from them.
Best wishes (hugs) x