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What is the duration of the 1st trimester of pregnancy?

The duration of the 1st trimester of pregnancy usually runs from the third through the twelfth week of pregnancy. Sometimes, calculating your 1st trimester is confusing because your doctor counts the weeks of the 1st trimester from the 1st day of your last period. So the 1st two weeks you are not pregnant, but they are still counted as part of the 1st trimester. The third week of pregnancy is usually when your egg is fertilized and your child conceived. After the egg implants in the uterine wall during the fourth week, it remain in an embryonic period until the tenth week. Development proceeds very quickly during weeks 11 and 12.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.