I think it probably depends on the time of year you are pregnant since February has less weeks but is still just a month. I would get out a calendar, honestly and just count from there.
All months have at least 4 weeks so I would consider 8 months to be at least 32 weeks pregnant. Granted, that would be 8 full months, not the start of 8 months. I think there's an average of 4.3 weeks per month so that times 7 is just over 30, so 31 weeks can be correct for the start of 8 months pregnant.
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