If Mary I's pregnancy had resulted in a child, and the child was a boy, England and Spain would be more closely tied than they are now. However, if Elizabeth I had married the Count of Anjou and had children, James I/VI would have simply remained King of Scotland and Elizabeth's surviving descendants would be on the throne. If Edward VIII had married a suitable woman and fathered a legitimate heir, Elizabeth II would never have been crowned Queen. There would probably be a King Edward IX on the throne instead...with perhaps another George, Prince of Wales and then the whole Charles and Diana thing probably would've never happenend...because...well...Charles would have been George instead.
If the salic law had been changed in Hanover, Queen Victoria would have ruled over Hanover and the UK, thus QEII would be ruling over more territory.
Mary I had two false pregnancies but never actually got pregnant. In august of 1555 her husband left for Spain he didn't return until 1557 when she had her second false pregnancies and in November 1558 she died.