How do you measure gestational age?
Gestational age
How to calculate gestational age formula?
Gestational age is a key indicator throughout pregnancy. An important factor to ensure the proper development of the baby. But how is it calculated?
To know when your baby will arrive, nothing could be simpler, just calculate your gestational age . " This is the period that has passed since the child was conceived ". For caregivers, it is a key indicator for measuring your baby's development.
What is gestational age? What does it have to do with weeks of amenorrhea?
Gestational age is simply " the time spent in the mother's womb". "It is generally expressed in weeks of amenorrhea (WA), and weeks of amenorrhea are the number of weeks since the first day of the last period before conception."
This is a theoretical term calculation . Especially since the calculation is imprecise if the mother-to-be has irregular periods.
Gestational age combined with growth parameters (height, weight, skull diameter) makes it possible to check that the future baby is developing well and to identify potential neonatal pathology.
What is the difference with embryological age?
Embryological age and gestational age are " two names that mean almost the same thing ," according to the midwife. " The difference is that embryological age is calculated in weeks of pregnancy (WG) "
Please note : 1 week of pregnancy (1 week of gestation) = 3 weeks of amenorrhea (3 weeks of gestation). In general, health professionals count in weeks of amenorrhea. In other words, the calculation is made from the presumed conception , and not from the start of the last period. This is two weeks less than the gestational age.
Note: In a woman with regular periods, pregnancy is considered to occur 2 weeks after the last period.
Another technique exists to calculate gestational age: the Ballard score . When gestational age is unknown, uncertain or when the infant seems too big or too small, doctors perform a complete physical examination of the newborn, performed within 24 hours of birth. This method has a margin of error of plus or minus 2 weeks.
Pregnancy calendar: how is the due date calculated? What is the use of ultrasound?
One of the interests of gestational age is to know the presumed date of delivery .
When the rules are regular, we therefore add:
- Date of conception + 266 days (embryologic age)
- The date of the first day of the last period + 280 days (gestational age)
This gives us an idea of our due date. However, this remains a theoretical calculation.
Note : The expected due date is also called “the expected term of the pregnancy”.
In women who have irregular periods, these calculations are impossible because we do not know precisely when ovulation took place (and therefore fertilization). In this case, and it is advisable to do a dating ultrasound that will allow to calculate the gestational age precisely. This is called an ultrasound calculation.
Almost all women go through this first ultrasound anyway , which should be done between 11 and 14 weeks of amenorrhea (later ultrasound estimates are less precise regarding the estimated gestational age). " At that time, we will measure the length of the embryo ". " We rely more on this ultrasound calculation, which is more precise to plus or minus 3 days ".
What is the normal gestational age of a future baby during pregnancy? At what weeks do we give birth on average? When is our newborn considered premature?
In summary, gestational age can be calculated based on:
- From the first day of the last period since conception
- From the presumed date of conception based on the last ovulation (embryologic age)
- From a fetal ultrasound (more precise)
- From the postpartum clinical examination
Logically, a gestational age called "at term" is 41 weeks (i.e. 39 weeks) . It is then considered that a baby is no longer premature from 37 weeks. " A baby can be born without any problem between 37 weeks and up to 41 weeks + 5 days. We always leave a small margin of doubt (compared to the initial calculation of the gestational age). However, we do not let a baby be born after 42 weeks".
Why? " We know that the end of pregnancy can be more risky, because the placenta has an expiration date. As it ages, it may not function as well, exchanges are less effective with the baby who receives less oxygen, fewer nutrients. " The delivery will therefore be induced .
How to calculate gestational age yourself during pregnancy?
To calculate the gestational age of your future baby at home , you need to know the date of the first day of your last period. You then need to count the number of weeks between that date and the current date.
If the first day of your last period falls on June 1st and today is August 1st, then your gestational age is 9 weeks.
To help you, you can consult the following table:
|
QUARTER |
MONTH |
WEEKS |
|
First quarter |
1 month |
6 SA |
|
|
2 months |
9 SA |
|
|
3 months |
13 SA |
|
Second quarter |
4 months |
18 SA |
|
|
5 months |
22 SA |
|
|
6 months |
27 SA |
|
Third quarter |
7 months |
31 SA |
|
|
8 months |
36 weeks |
|
|
9 months |
41 weeks or even 42 weeks |
If you prefer to calculate the embryological date, you will need to estimate the date of conception . To do this, you must identify the period when you ovulated. This can be found out through hormonal tests, by observing your cervical mucus , which looks like egg white, on the day of ovulation, or by measuring your basal body temperature.
If you ovulated on June 1st and it is August 1st, your embryological age is 9 weeks (or 11 weeks).
