To think I can hide this?

It’s not her first pregnancy though.

Depends.
Some women don't really show, especially with first child.
I am 175, size 10 pre first and able to wear same high raise skinny jeans at 25 weeks.
Second one was whole other story.

Would something like this work for the wedding?

https://www.debenhams.com/product/yumi-yumi-urban-green-floral-print-kimono-midi-wrap-dress_p-1e23d38d-b07a-4f78-bc41-121f0f0eab12?colour=Green&size=16&istCompanyId=76f7277d-6e78-4dc2-aaff-1eb77fae16b0&istFeedId=258a4886-8f3c-47ef-9369-d1eda8d84501&istItemId=rqqaappmi&istBid=t&gad_source=1&gclid=CjwKCAjw57exBhAsEiwAaIxaZjmx9LerueSKN9oektYDC4sO_10bTVtK3TQmiqYzUE_sKWgCF7SbVRoCizoQAvD_BwE&gclsrc=aw.ds

Disclaimer: I haven't RTFT.

Even if you can physically hide the 'bump' how are you planning to explain that you can't use the hot tub sauna? If you're having any treatments, you'll need to declare it as back massages are a no.

I get it OP, I had a miscarriage at 12 weeks after telling family and some friends. If I get pregnant again, then I think I would like to keep it quiet until 20 weeks too, maybe even longer.

For the spa day, if anyone asks why you aren't in the steam room etc, could you not just say that you're playing it safe as you're in the two week wait period? Matter of factly? Would your mum and sister in law be surprised that you were trying again?

Congrats and best of luck for your next scan 🤞

Trying to think of reasons not to use the steam room etc - could you say you’ve recently had low blood pressure and been advised to avoid till it’s sorted out? Or if this would cause your mum too much alarm, how about good old athlete’s foot or verrucas or similar? And as others have said, book a massage or facial or nails or similar so you can still take part in the day. Wedding should be ok with suitable loose-fronted dress.

A family member of mine wanted to announce her pregnancy whilst we were on holiday together but on a specific anniversary date which fell at the end of the holiday so we spent a few days together pee-announcement. She was at 19 weeks and I noticed the bump straight away when I saw her despite her trying to hide it. I didn’t say anything as felt it would be rude to ask about it if she was obviously choosing not to announce and I pretended to be surprised when she announced the pregnancy. That said I think some of the other family members were genuine.y surprised and hadn’t noticed though. This was in winter though so she was wearing big jumpers, I imagine a pregnancy would be hard to hide in swimwear.

I think you’ll be fine at the wedding, but it will be hard at the spa. It’s sometimes harder to hide around people you don’t know as if one of your SiL’s friends realises you’re not using anything like the sauna etc. they can sometimes just blurt it out without thinking, e.g. oh are you pregnant then? Where as close friends and family can be more tactful and especially given the past might realise but wouldn’t say anything.
I would suggest trying to get a mid morning slot and getting your nails done as you can’t then use the pool/jacuzzi for a few hours afterwards.

I've previously been a beauty therapist. Youl be fine to have a facial. If you need to fill in the form infront of anyone else just say when you go in to the treatment room you're actually pregnant but no one knows so to leave any steps out that aren't compatible with pregnancy.

Youl likely all get robes so can stay wrapped up and just chill on a lounger. Lots of people don't use the sauna, steam room or jacuzzi anyway so wouldn't worry about that.

You could wear something ruched at the tummy like this, I appreciate darks not very spring weddingy but the dark colour would help conceal a bump

op, you run the risk of a staff member mentioning it. Personally I’d just call off sick, say you’ve the shits, and let your mum and sil go on their own.

It really depends what the facilities are like but I went to one recently with pregnant sil and she could only really do the relaxation room and the foot baths.

You are advised to avoid hot tub, sauna and steam rooms

Would something like this work OP?

https://www.simplybe.co.uk/shop/p/vb589?optionSize=14&promo=6202&gad_source=1&gclid=CjwKCAjw57exBhAsEiwAaIxaZthHEm4-n1YtwgKUxJ8pd4JnEybTmtdTWLe6TKupolUyhqYS_l3DxRoCPFIQAvD_BwE&gclsrc=aw.ds

Congratulations on the pregnancy OP, hope everything goes well for you with the scan.

The skirted costume idea sounds good, also try to keep your robe on as much as possible as that will hide it quite well.

As for practicalities I would recommend ringing the spa to ask about the treatment options and also ask them to make a note on the system that the pregnancy is secret at the moment so to not mention it in front of any people.

Can you afford to book a private scan in the next few days? You can still attend your NHS one of course, but it will set your mind at rest about being safe to share the news before your Spa day.

Much more likely to steal focus if people suspect and start asking questions at the wedding.

Given your history OP, consider calling the specialist screening midwives and see if they can arrange your anatomy scan at 18 weeks to support your mental health.

Surely, SIL and your mum will understand that you want to keep quiet until your scan and don't want to 'steal' the wedding. So share your news but swear them to secrecy. Avoid the treatments not recommended for pregnant ladies. Find a floaty, A line dress for the wedding.
It's exciting but you can contain it. I went to a wedding expecting and no one had any idea.