How to calculate gestational age based on embryo size?
The gestational age and fetal age can effectively infer the expected date of delivery of a pregnant woman, so both are very important.
It turns out that gestational age and fetal age are not the same, and the calculation methods of the two are also different.
Let’s discuss it together!
Gestational age refers to the period from the time when the egg cell and sperm combine to form a fertilized egg to the time when the fetus is delivered from the mother’s body. Generally, the expected date of delivery is when the gestational age reaches 38 weeks.
Therefore, in the first two weeks of pregnancy, the embryo has not yet appeared. The follicles are still developing during these 14 days and ovulation has not yet occurred, but the calculation of gestational age has already begun.
The menstrual cycle can be long or short. Calculating gestational age based on the date of the last menstrual period is a rougher method of calculation than fetal age.
Because we can only calculate the date of the last menstrual period, but we cannot know the exact date of the sperm and egg combination.
According to international practice, gestational age is calculate from the last menstrual period. Doctors usually only describe the gestational age, not the gestational age. In real life, the accurate gestational age is not a big concern, but in some prenatal fetal tests, accurate gestational age is more important.
▽ Gestational age is calculate
based on the last menstrual period (LMP) day:
The month of the last menstrual period plus 9 is the month of the expected date of delivery. The day of the last menstrual period plus 7 is the day of the expected date of delivery.
The example is as follows: Last menstrual period: February 1, 2019 Month: February 2019 + September = November 2019 Date: 1st + 7th = 8th Due date: November 8th, 2019
But it also has prerequisites: Assume that all women meet the following conditions: ✔ Pregnancy for 280 days ✔ 28-day menstrual cycle ✔ Regular menstrual cycle ✔ Ovulation and fertilization on the 14th day ✔ No recent use of hormonal contraceptives ✔ Correct memory
Calculation of gestational age
Compared with the traditional method of calculating gestational age based on the last menstrual period, calculation by B-ultrasound is more direct and accurate. The following will focus on the method of calculating gestational age by ultrasound.
First, the diameter of the gestational sac (GS) or the crown-rump length (CRL) of the fetus, i.e. the length of the embryo, is measured by B-ultrasound to estimate the gestational age .
The crown-rump length (CRL) is measure in the midsagittal plane, when the whole embryo is fully display, in the middle position during the transabdominal or transvaginal scan. The average of three measurements is take to reduce the error. After measuring the two values of the gestational sac (GS) diameter or the crown-rump length (CRL) of the fetus, the doctor will use the clinical data to estimate the gestational age. But there may be slight differences if different reference data are use to estimate the gestational age.
Generally, we refer to some authoritative literature to calculate the accurate gestational age. The following reference data for calculating the gestational age is obtain from an authoritative foreign literature.
Example
For example: If the B-ultrasound shows that the fetal crown-rump length (CRL) is 1.0 cm, the estimated gestational age is 7.1 weeks (50 days). The fetal crown-rump length (CRL) grows by 0.1 cm or 1 mm every day.
Gestational age is important for fetal DNA testing ! The Gestational age is important for fetal DNA testing! Gestational age is important for fetal DNA testing!
Because insufficient fetal age may result in insufficient fetal DNA being extract, it will have a significant impact on the test results and accuracy.
It is hope that pregnant mothers can meet the minimum requirement for the number of weeks for DNA testing before undergoing the test. The number of weeks provided is the accurate gestational age calculate from the data after the B-ultrasound examination, rather than the gestational age inferred based on the last menstrual cycle.
