Fetal Development: Week 1

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Gestational Age: Week 1

In pregnancy, the calculation of the gestational age of your baby and the due date begins with this week, which starts with the first day of your last menstrual period; therefore, technically, you are not yet pregnant at this stage, as you should be menstruating this week.

For calculation purposes, you’re “pregnant” before you even conceive!

Gestational Age week 1

Gestational Age vs Conceptional Age

“Gestational age” is the time between the first day of your last normal menstrual period and the day of delivery. 

This estimation assumes that conception occurs on day 14 of your menstrual cycle. But the time of ovulation varies greatly in relation to the menstrual cycle, both from cycle to cycle and individual to individual. With the result that only 4% of all babies are born precisely on the estimated date of delivery (EDD).

If you have a regular 28 day cycle, the first day of your last menstrual period (LMP) occurs approximately 2 weeks before ovulation and approximately 3 weeks before implantation. 

Because most women know when their last period began but not when ovulation occurred, traditionally the gestational age has been used when estimating the expected date of delivery (EDD).

“Conceptional age” (true fetal age) is the time between the day of conception and the day of delivery.

Therefore gestational age is 2 weeks longer than conceptional age.

Source: American Academy of Pediatrics, e-medicine.

Tip for Week 1

In preparation for pregnancy, discuss with your doctor what prenatal multivitamin to add to your daily routine to supplement your healthy diet.

Folic acid can help prevent neural tube birth defects that affect your future baby’s brain and spinal cord. Iron and calcium are important too.

Some prenatal multivitamins can cause nausea, so you do experience morning sickness later, you can change to a different kind of prenatal vitamin or use a different form such as a chewable or liquid multivitamin rather than one that you swallow whole.

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