What should I do if the due date and the ultrasound are half a month apart?

When we go for a B-ultrasound examination, the B-ultrasound examination sheet will show a pregnancy period, and we can use this cycle to infer the date of delivery. Some expectant mothers will ask, "How many days are there between the estimated due date from ultrasound and the actual due date? Which one is more accurate?"

Theoretically speaking, the date of delivery calculated by B-ultrasound is more accurate, because B-ultrasound represents the specific situation of the baby's growth, while the date of delivery calculated by ourselves is only a relevant and approximate estimated time. Everyone's menstrual cycle, ovulation time, and pregnancy days are different. Using the standard calculation method to estimate the due date cannot guarantee accuracy for everyone.

How to calculate the due date

Traditionally, the due date is calculated as follows: the first day of the expected due date of pregnancy is the starting and ending time, and the due date is calculated from the first day of pregnancy to 280 days in the future.

We can easily find such due date calculation software on the Internet, enter the due date of pregnancy, and the software will automatically calculate the due date, which is convenient and easy to use.

B-ultrasound examination to estimate the expected date of delivery

Use the data from the ultrasound examination form to calculate the gestational age in weeks or days. If it reaches 40 weeks or 280 days, it is the due date.

1. Calculation based on fetal sac

The method of calculating gestational age based on the gestational sac is as follows: if the gestational sac has 3 marked values, then the sum of these 3 values ​​divided by 3.25; if the gestational sac has 2 marked values, then the sum of these 2 marked values ​​divided by 2.25.

I used the ultrasound check report to calculate, and the standard value of the gestational sac was 2.3*2.1 cm, so the number of weeks of pregnancy = (23 21)/2 25=47 days, but the number of days of pregnancy I calculated myself was 51 days, which is 4 days off.

2. Calculate based on fetal bud and fetal heart rate

Weeks of pregnancy = length of embryo bud and fetal heart rate 6.5.

For example, the ultrasound examination shows that the single embryo bud fetal heart rate data is 0.9 cm, so the gestational age = 0.9 6.5 = 7.4 weeks, which is 51.8 days, which is only 0.8 days away from the actual gestational age of 51 days.

3. Calculate based on arm-head diameter

Gestational weeks = brachiocephalic diameter 6.5

4. Calculate femoral length based on biparietal diameter

The gestational age can be checked based on the data of biparietal diameter and femur length, but the error will be relatively large.

16 weeks: Biparietal diameter is 3.4 cm, femur length is 2.1 cm. According to the biparietal diameter, it is close to between 15 and 16 weeks, and according to the femur length, it is 16 weeks.

26 weeks: Biparietal diameter 6.1 cm, femur length 4.4 cm. The biparietal diameter is close to between 24 and 25 weeks, and the femur length is 24 weeks.

32 weeks: Biparietal diameter 8.1 cm, femur length 5.8 cm. The biparietal diameter is close to the middle of 31 and 32 weeks, and the femur length is between 30 and 31 weeks.

38 weeks: Biparietal diameter 9.4 cm: Femoral length 7.1 cm. The biparietal diameter is over 40 weeks, and the femoral length is 37 weeks.

in accordance with

Based on the calculation of actual cases, the difference between the expected date of delivery and the actual date of delivery calculated using the embryonic bud, fetal heart rate and brachiocephalic diameter is the smallest.

The second method is to use the gestational sac to calculate the expected date of delivery, with an error of within 5 days.

The least accurate method is to use biparietal diameter and femoral length to check the date of delivery. Multiple data are intertwined and it is impossible to obtain an accurate result.