Hi. it very much depends on what he was treated with. Some drugs have a higher infertility risk than others (what was he treated with if you don't mind me asking?)
Since you're pregnant (congratulations) he isn't infertile, which is the biggest risk with chemo. Most chemo treatments attack fast dividing cells - that includes the progenitors to sperm, which results in lowered sperm count while treatment us progressing and for a few months/to years after. The big risk is knocking out all those stem cells - your pregnancy indicates this hasn't happened so that's one big positive!
Assuming he's been off the treatment for a few months (is that correct?) it's likely his sperm count has bounced back. I'm not 100% sure but I think I remember reading a study a while back that indicated that there was no statistical effect on chromosomal abnormalities in children of cancer survivors. Let me have a look through the literature if I have a moment today and I'll get back to you later.
My gut feeling (highly unscientific) is that infertility is the biggest potential hurdle. You've overcome that so unless you conceived during or very shortly after treatment, I don't think you're at any higher risk.
Congratulations to the both of you - melanoma is an absolute bastard.
I would see if you can get in touch with the consultant he has been under for the treatment as they would have the best info to if there are any potential risks and if you need any additional monitoring. Also make sure it's noted with your midwife, they will generally ask about certain medical conditions within the parents or immediate family.
Congratuations, it must be a lovely bit of good news for you both.
There's not much data on pregnancies about that whole class of drugs to be honest. They're very new, and they're very strict about contraception on all the trials I've worked (not because of anything specific about this drug, that's just how trials are.)
Couple of studies that show that pregnancies started by young men have no greater risk than others but I think it was a small sample. Anyway, they're not genotoxic on the way "standard" chemo is.
I found that bit before the 13 week testing the most nerve wracking part - I hope you'll have good news and strongly suspect his consultant is going to say that they'll monitor you but they don't have specific concerns...it's more that these drugs are so new, there just isn't enough data. Definitely speak to the consultant though, and the counsellor. I would certainly use condoms even though you've conceived as well - no idea if it gets into seminal fluid but if it does you don't want to be exposed to it.