Congratulations 
Ultimately it’s what ever you feel comfortable with but I had a not too dissimilar situation however I do have lots of family around for support (I’ll come back to that).
When we found out I was pregnant I was in the 3rd year of 4 year integrated masters degree, DPs step sister also is going through IVF (2nd round). DC is now 9 weeks old so..
I had to defer some uni work until this year, uni were great and very accommodating even now they’re allowing me more time if required but I want to get it done. Whilst pregnant I think it was the hormones but I just couldn’t concentrate, all I could think about was DC. It was the best decision to defer because to me.. the knowledge understanding and grades is more important that adding an extra year.
DPs step sister was unbelievably understanding and very interested in everY stage, bought us lovely gifts after birth and has taken a real interest since. I was very nervous telling them as you are but what I kept in mind is, they’re going to those huge lengths to get pregnant because they love and yearn for children. Even if upset initially or maybe jealous initially they’re bound to be happy for you because they understand how lovely it is/would be.
I’m not sure how I would have coped the first few weeks without family around, DP had 6 weeks off work with us and almost all of my family is off for one reason or another (retirement, school hols, furlough, wfh) so I’ve had places to go catch a break whilst someone else cuddles DC for a while, those moments have been a lifeline for me.
You’re not in a rush to make a decision, take your time and think it through. Don’t feel forced into a corner because of what you think it might be like. Just go with what you truly want.