Understanding pregnancy dating
How far along am I?
Pregnancy weeks are usually counted from the first day of your last menstrual period. An ultrasound can help a clinician check that estimate.
The starting point
Your pregnancy timeline begins with your last period.
Gestational age describes how far a pregnancy has progressed in weeks and days. The usual calendar starting point is the first day of your last menstrual period, rather than the day you had sex or took a positive test.
An estimated due date is generally 40 weeks from that starting point. Your clinician may use ultrasound findings to establish or confirm the date.
Source: ACOG’s explanation of pregnancy due datesLast period
The first day of your last menstrual period provides an initial starting point.
Clinical assessment
A clinician considers your menstrual history and available ultrasound findings.
Estimated date
The findings help establish your gestational age and estimated due date.
What if I don’t know the date of my last period?
Tell your clinician if your periods are irregular or you are unsure of the date. First-trimester ultrasound can help estimate the due date when the menstrual date is uncertain. An estimate from an app or calendar does not replace a clinical assessment.
Source: ACOG, How Your Fetus Grows During Pregnancy
How can First Coast help?
Start with a free clinical pregnancy test. After a positive test, request a free limited ultrasound with the form below, by text or by phone. You can also book a confidential information appointment to discuss your questions.
Bring the questions that matter to you.
- How was my gestational age estimated?
- Do I need another visit or additional medical care?
- What does this information mean for my next steps?
Website information is educational and does not replace individual medical care.
Free limited ultrasound
Looking for an ultrasound?
Ultrasounds are available after a positive clinical pregnancy test. Ask the way that’s easiest for you, and our team will check eligibility and help you find a time.
No positive test yet? Book a free pregnancy test first.
Share your name, phone number and email, and mention you’d like an ultrasound. Our team will contact you about eligibility and scheduling.
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First Coast Women’s Services
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