Ah, unfortunately I have no idea how to advise you @Sev100 . But have you told the Perinstal Mental Health Team how you feel? If they say that they still think it is a good idea to keep an eye on you, have you asked them (in a calm manner of course) why they think it is a good idea, and what "keeping an eye on you" (or whatever more professional phrase they use) actually means - how intrusive it is going to be?
From my point of view (as a mother and grandmother) I do know that some people can feel elated while they are pregnant and then come crashing down when the baby is born, and the hormones change, and of course exactly the same thing can happen in reverse. Then other people might stay elated during both their pregnancy and new mum states, and gently start getting back to - a new - normal once their hormones settle, and they get more used to having a baby. Of course, some people will struggle with pregnancy, and struggle afterwards. The reality for most, is probably a mixture of a few of those things.
Of course very few perinatal medical teams will have any idea how their "mums" will be, especially if it is the mums first pregnancy. However, if you try and look at it from the P.T.s point of you (as if you worked for them, and were not pregnant yourself), and you found out through a GP's records that one of your mums had had particular difficulties with their mental health previously, and if you were lucky enough as a member of that team, to have a section that focuses on the mental health of the mums, then on reading those records I would imagine that you would want to offer that mum extra support, and would therefore tell the P.M.H.T. about your new pregnant mum-to-be?
If after you have - very reasonably - clarified how the mental health team want to be involved with your care, you will hopefully be able to make a more informed decision about whether you want, or think that there is any possibility that you might benefit from, their help.
I have to say, that I wish for at least my first pregnancy, I had had some extra support, as looking back now, even though I loved being pregnant, and I loved my baby totally when she was born, I think that I did suffer from pnd - thankfully not as badly as some people - but I was very scared and unhappy, and felt that I was getting, or I was at least potentially getting, everything that I did for my baby wrong. I had a reasonable amount of support from my mum (but she lived over an hour away and worked full-time), and my husband, but he also (thankfully) had a full-time job, and my heath visitor always, and inexplicably, turned up dressed to the nines, and wearing a velvet jacket, so I never felt like I could ask her for help, or even to hold my baby for a minute or two while I did something else, like fetch a new babygrow!
So, as long as you feel comfortable with it, and still in control, I think that in your position I would accept some extra support, but on the proviso that they would respect my decision if I felt they were becoming too intrusive. Good luck with the rest of your pregnancy @Sev100 you sound to me like you are going to be an excellent mum - but to me the very best mums are the ones who recognise if, and when, they need a little help or advice, and they accept it, if it feels right.
❤️💐xx