@IPineapple
I'm sorry you had to go through this, and that it will probably happen again, because sadly, some people have no emotional intelligence, and no thought for other peoples feelings. And if you get upset/offended, it's because you're too sensitive, or you need to lighten up. 
Not sure if I'd report it, if it was just once, but if she - or any other nurses at your practice say anything else similar to this, then definitely complain.
I have one child - now in her mid 20s - but I am not going to discuss on here why me and DH had just the one.
Although we have not had any comments since she hit her mid teens, (over a decade ago;) we spent the first 13-14 YEARS of her life, being bombarded with comments from nosey, intrusive, opinionated individuals, who thought it was appropriate to not only ask us when we were having another baby, but also to say we were stupid, selfish, and WRONG when we said we were having just the one. With cries of how lonely, spoilt, and bratty she will be. And how cruel it was to not give her a sibling. 
Some people got a pretty short shrift from me and DH, and got told (by us) to mind their own business, and that it was nothing to do with them why we were not having any more children.
I even had a couple of work colleagues (some 20 years back,) who had two secondary school age kids each, who came out with a constant stream of comments like 'you will change your mind,' and 'no more kids? you can't do that to your daughter! No brothers or sisters awwwww.'
I said clearly (a number of times,) 'me and my husband are NOT having any more children, so please stop asking me when we are having the next one, because it's actually fucking offensive,' and they drew breath in and stared wide eyed and said 'ooooooooh, someone's upset! No need to be like that Patti!' I just ignored them and left the room.
Then a few weeks later, the same fucking women started off again. I'd say 'I'm starving' (as it was near lunchtime,) and they'd say 'ooooh, pregnant are ya? Ahhhhh your daughter will have a little brother or sister, how lovely.' 
I also had a few similar comments from nurses, and health visitors etc, when she was a baby/toddler, and even from a couple of TEACHERS when she was at primary school. 'Awww, you can't have just the one child.' Followed by looking at my daughter, and saying 'not fair is it, tell mummy you want a brother or sister!' I did laugh though when DD said 'No I won't, because I don't!'
As I said, I don't know WHY people think it's OK to spout shit like this. I would never DREAM of it. These are the same tits who say 'awwww, what a shame you've had another BOY' when someone has their second or third baby boy... (and they have no girls.) And 'awwww what a shame you don't have children' to women who are child free... 
Mind you, these 2 women at my old workplace didn't just target me, and were a bit obtuse and insensitive towards others. One of them said once - to a child free woman who worked there - 'awww, what a shame you have no children. You'd make a wonderful mother!' And the priceless doozy 'you should have a child. Having children makes you a better person.' 
As I said, obtuse and insensitive.