Please help us. Unexplained infertility

Hubby and I have been ttc for about 2 years. We got pregnant ONCE with IVF but lost bubs at about 4 weeks.

Hubby wants to try more tests before second round of IVF. What else can be done?

We have done sperm check, tubes, ahm, the lot. All come back clear.

Please help us with ideas.

Many thanks