The discussion was about "after the baby is born" so one cannot be pregnant again right after the baby is born
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On a more serious note, there are 2 choices if the wife is pregnant -
1) The wife can take the medical test (blood/urine/vision etc) but skip the chest X-ray and the application can be submitted with a LOE. The wife can take the chest X-ray after the baby is born and then ask the clinic to submit this to IRCC.
2) The wife can go ahead and take the chest X-ray with a lead apron so that the X-rays do not damage the fetus + the other tests and submit the application to IRCC.