Inside Pregnancy: Weeks 1-9 | BabyCenter
The first week of the month is the seven days starting with the first day of the month. Hence, in your example, the first week would be Tuesday, the 1st through Monday, the 7th.
The first week of the month is the seven days starting with the first day of the month. Hence, in your example, the first week would be Tuesday, the 1st through Monday, the 7th.