Update from me - decided to get second jab yesterday, I’m just over 15 weeks.
Interestingly I had two clincians refuse to give it to me due to their concerns re lack of data. But I have done my research and shared info I had received from an Immunologist I had reached out to (as I was getting nowhere with GP and midwives) and it convinced the second clinician to give it to me. In case it is useful to anyone else, please see the Immunologists email below;
“It's worth saying that in terms of getting vaccinated under our national programme, you would have to get AstraZeneca as your second dose. However, it is possible to get Pfizer as a second dose if a doctor writes you what is called a "patient specific directive" (basically a prescription), which allows you to get a vaccine that is not recommended by the national schedule. The doctor would, of course, have to be convinced that it is important for you, clinically, to get a different vaccine from usual - this is most often used when people have had a bad reaction to their first dose.
So be aware that that is an option, but if I were in your position I would prefer to have my second dose of AZ as per the national schedule, and my main reason for this is that we know lots about what happens with two doses of AZ, but much less about what happens with AZ followed by Pfizer. So I personally would prefer to go with the option about which there is more information available.
I should also say that I do think it's worthwhile getting a second dose of something, whichever you choose, since once dose is not as protective against the delta variant as we would like, whereas two work very well.
In terms of specific information about AZ in pregnancy, the reason we started recommending Pfizer/Moderna rather than AZ in pregnancy is because the biggest safety in pregnancy datasets come from the USA and Israel, which are using those vaccines. However, there is pregnancy safety data on AZ from the UK and Canada, and this has given us no reason to think AZ is unsafe - it's just that we have more data on the mRNA vaccines in pregnancy because the USA and Israel led the way in that, so we feel more confident about them.
It's also worth knowing that AZ has been designed not to leave the site of injection, and all the animal data we have bears this out, so we do not worry about it crossing the placenta. Because of this, we have been happy to use vaccines similar to AZ in pregnant people in the past, to prevent Ebola.
Finally, you may be worried about the rare clotting side effect associated with AZ. The first thing to say is that it is rare, and rarer still on the second dose. The second is that, even though clotting is more common in pregnancy, pregnancy-associated clotting actually occurs via a different mechanism to the rare side effect, so being pregnant does not put you at higher risk of it. Finally, now that we know about this, we are actually very good at treating it.”