If an event occurs on a given date during a woman's pregnancy, then the gestational age at that moment can be calculated based on the ultrasound dates as determined on a separate date.
Example of an event: blood sample collection, trauma, drug exposure
Data entry:
(1) event date
(2) ultrasound date
(3) gestational age based on ultrasound in weeks and days
If the date of ultrasound is before the event date,
days between event and ultrasound =
= (event date) – (ultrasound date)
If the date of ultrasound is after the event date,
days between event and ultrasound =
= (ultrasound date) – (event date)
date with t=0 based on ultrasound =
= (ultrasound date) – (7 * (weeks of gestation)) – (days of gestation)
weeks of conception at event =
= INT(((event date) – (date t=0)) / 7 )
additional days of conception at event =
= (event date) – (date t=0) – (7 * (weeks of gestation at event))
