How is the due date worked out?
The due date is the first day of the last period plus 280 days (40 weeks). If the conception date is known, 266 days are added to it. In IVF pregnancies the transfer date and embryo age are used: 261 days are added for a day-5 transfer and 263 for a day-3 transfer.
Will my baby be born on this date?
Not necessarily. The due date is a reference point. Babies born from 37 weeks are full term, and most births happen within two weeks either side of the due date.
Why might the date change?
If the baby's size on the first-trimester scan differs clearly from the date based on your last period, the due date is corrected to the scan. Later scans are not used to change the due date.
Frequently Asked Questions
Which method is most accurate?
For IVF pregnancies, the transfer date; for other pregnancies, the last period confirmed by a first-trimester ultrasound.
What happens if I go past my due date?
The baby and placenta are monitored more often, and the timing and method of birth are planned with your doctor.