### Description

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))

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