It’s a common scenario in early pregnancy: you have one due date based on your last menstrual period (LMP), and then after your first ultrasound, you're given another. So, which one is correct? This tool is designed to demystify that process. It uses the official guidelines that doctors and midwives follow to 'reconcile' these two dates into a single, official Estimated Due Date (EDD) that will be used for the rest of your pregnancy.
Understanding this process can bring clarity and confidence as you begin your pregnancy journey.
How to Use the Due Date Reconciliation Tool
To determine your official EDD, this tool needs the same information your doctor uses after your first-trimester dating scan:
- Your Last Menstrual Period (LMP) Date: Enter the first day of your most recent period.
- Your Ultrasound Date: Enter the date on which your first-trimester ultrasound was performed.
- Gestational Age from Your Scan Report: Find the gestational age (in weeks and days, e.g., 8w 3d) on your ultrasound report and enter it here.
The tool will then compare the due date calculated from each method and apply the standard medical guidelines to tell you which one becomes your official EDD.
The ACOG Guidelines Explained
Your healthcare provider doesn't just pick a date; they follow evidence-based guidelines from The American College of Obstetricians and Gynecologists (ACOG). The guidelines are based on the fact that ultrasound is most accurate in the early first trimester. Here’s a simple breakdown of the logic:
- For Ultrasounds Before 9 Weeks: If the difference between your LMP due date and ultrasound due date is 5 days or less, your doctor will typically stick with your original LMP date. If the difference is greater than 5 days, they will change your official due date to the one from the ultrasound.
- For Ultrasounds Between 9 and 14 Weeks: The acceptable range of difference is slightly larger. If the discrepancy is 7 days or less, they will stick with the LMP date. If it's more than 7 days, the ultrasound date becomes the new official due date.
Why a Single, Official Due Date is So Important
Establishing a final, accurate due date is one of the most critical steps in your prenatal care. This single date becomes the anchor for your entire pregnancy timeline. It ensures that crucial genetic screenings are performed during their effective windows, that your baby's growth is monitored against the correct standard, and that your care team can make the best decisions late in pregnancy, such as managing a pregnancy that goes past 41 or 42 weeks.
Important Medical Notes
This tool is designed for educational purposes to illustrate the process of due date reconciliation based on ACOG guidelines for first-trimester ultrasounds. The final, official Estimated Due Date is the one that is confirmed by your healthcare provider and entered into your medical chart. Always rely on your doctor for all aspects of your prenatal care.