03/07/2025
You calculated 32 weeks…
The scan says 36 weeks…
Your midwife says 30 weeks…
Wow, you’re lost. Let me explain what happened.
Pregnancy dates can be confusing, especially when your period, your scan, and your midwife don’t seem to agree. But here’s why that happens and how to understand it better.
Why the Dates Don’t Always Match
1. Your LMP might not be accurate
If your menstrual cycle is irregular, or you don’t remember the exact first day of your last period, your calculation could be off by a few weeks.
2. The scan gives an estimate based on baby’s size
Ultrasound uses your baby’s measurements to estimate the gestational age. This works best in early pregnancy. Later scans can be less accurate because babies grow at different rates.
3. Midwives combine both history and scan findings
Your midwife looks at your cycle history, your scan, and sometimes even your fundal height (tummy measurement) to decide what’s most reliable.
So Which One Is Correct?
The most accurate dating usually comes from a first-trimester scan (before 13 weeks). If that wasn’t done, your due date is based on your last menstrual period or the next best early scan available.
By the third trimester, scans can overestimate or underestimate the baby’s age because every baby grows at their own pace.
The goal is not to get stuck on the number of weeks. It is to monitor your baby’s growth and your health. Let your midwife guide your care based on the most reliable information available.
– Midwife Chiamaka
