Actually, it is possible to file a Married Filing Separately (MFS)
tax return, and then later amend it by filing a Married Filing Jointly
(MFJ) tax return. This is true for all taxpayers, and not specific only
to filers whose spouse happens to be a foreign national. While the
Internal Revenue Service (IRS) allows taxpayers to file as MFS, and then
later amend by filing MFJ tax returns, the reverse is not permitted as a
matter of law, after the normal April filing deadline.
Additionally, however, because you are married, and your spouse does not yet have a SSN or ITIN, then you would have to paper-file such a MFS tax return by manually writing
"nonresident alien" or "NRA" in the space(s) where your spouse's information is required. You could not e-file such a tax return.
That
said, you do have some, perhaps easier, options than to file MFS now and
later amend as MFJ. First, you could just request a simple
extension of time to file your original tax return. That would give you
an extra 6-months to apply for and receive your spouse's SSN or ITIN, as well as such a number for your new child.
Instructions
on how to file an extension (from overseas) can be read at the following link:
https://ttlc.intuit.com/questions/3895790
More information on the choices of how to file a tax return with a foreign spouse are discussed
in much greater detail at this link:
https://ttlc.intuit.com/questions/3839499
Thank you for asking this important question.
