Fetal Weight Calculator

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Biparietal diameter (cm)

Abdominal circumference(cm)

Femur length (cm)

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Introduction to the Fetal Weight Calculator:

1. About Biparietal Diameter (BPD)

(1) The fetal weight calculator is based on parameters measured by B-mode and color Doppler ultrasound. It uses a formula for fetal weight calculation (biparietal diameter × abdominal circumference × femur length) and displays the results in pounds (lb) and kilograms (kg).

(2) During fetal development, the fetal weight calculation formula is only predictive. Generally, there may be a margin of error of ±10–15% between the actual birth weight and the predicted weight.

2. About the Occipitofrontal Diameter (OFD)

(1) The occipitofrontal diameter, also known as the "anterior-posterior diameter," refers to the longest part of the fetus's head from front to back, specifically the distance from the "nasal root on the forehead" to the "occipital protuberance at the back of the head."

3. Regarding Head Circumference (HC)

(1) Fetal head circumference refers to the maximum circumference around the fetal head, representing the longest distance from the front to the back of the head.

(2) Generally, the longest distance is from the "nasal root of the forehead" to the "occipital protuberance at the back of the head"; therefore, the head circumference is typically measured as the length of a full circle from the "nasal root of the forehead" to the "occipital protuberance at the back of the head."

4. Regarding Femur Length (FL)

(1) While lying on her back, the expectant mother allows the physician to measure the distance from the fundus of the uterus (near the lower edge of the sternum) to the upper edge of the symphysis pubis to estimate the fetus’s growth.

(2) Once pregnancy reaches 20 weeks or more, the gestational age usually corresponds to this measurement.

5. About Abdominal Circumference (AC)

(1) Measure the highest point of the abdomen horizontally. However, since abdominal circumference varies significantly among expectant mothers, it is recommended that mothers take regular self-measurements at home.

Fetal ultrasound normal parameter values

gestation period	Biparietal diameter (mean) cm	Abdominal circumference (mean) cm	Femur length (mean) cm
13 weeks	2.52 pounds 0.25 pounds	6.90 l.65	1.17 pounds 0.31 pounds
14 weeks	2.83 per cent 0.57 per cent	7.77 1.82	1.38 p.m. 0.48 p.m.
15 weeks	3.23 p.m. 0.51 p.m.	9.13 pesos 1.56	1.74 per cent 0.58 per cent
16 weeks	3.62 p.m. 0.58 p.m.	10.32 pesos 1.92	2.10 pounds 0.51
17 weeks	3.97 pesos 0.44	11.49 p.m. 1.62 p.m.	2.52 per cent 0.44 per cent
18 weeks	4.25 pounds 0.53	12.41 l.89	2.71 p.m. 0.46 p.m.
19 weeks	4.52 per cent 0.53 per cent	13.59 2.30	3.03 pence 0.50
20 weeks	4.88 per cent 0.58 per cent	14.80 l.89	3.35 p.m. 0.47 p.m.
21 weeks	5.22 p.m. 0.42 p.m.	15.62 p.m. 1.84 p.m.	3.64 per cent 0.40 per cent
22 weeks	5.45 p.m. 0.57 p.m.	16.70 S2.23	3.82 pesos 0.47
23 weeks	5.80 pesos 0.44	17.90 per 1.85	4.21 p.m. 0.41 p.m.
24 weeks	6.05 pence 0.50	18.74 S2.23	4.36 p.m. 0.51 p.m.
25 weeks	6.39 pesos 0.70	19.64 s.2.20	4.65 p.m. 0.42 p.m.
26 weeks	6.68 p.m. 0.61 p.m.	21.62 per cent 2.30 per cent	4.87 pesos 0.41
27 weeks	6.98 p.m. 0.57 p.m.	21.81 pesos 2.12	5.10 p.m. 0.41 p.m.
28 weeks	7.24 pounds 0.65	22.86 2.41	5.35 p.m. 0.55 p.m.
29 weeks	7.50 p.m. 0.65 p.m.	23.71 per 1.50	5.61 p.m. 0.44 p.m.
30 weeks	7.83 p.m. 0.62 p.m.	24.88 s.2.03	5.77 p.m. 0.47 p.m.
31 weeks	8.06 pes 0.60	25.78 2.32	6.03 p.m. 0.38 p.m.
32 weeks	8.17 s.0.65	26.20 S2.33	6.43 p.m. 0.49 p.m.
33 weeks	8.50 pesos 0.47	27.78 2.30	6.52 p.m. 0.46 p.m.
34 weeks	8.61 p.m. 0.63 p.m.	27.99 2.55	6.62 p.m. 0.43 p.m.
35 weeks	8.70 per cent 0.55 per cent	28.74 2.88	6.71 pesos 0.45
36 weeks	8.81 p.m. 0.57 p.m.	29.44 2.83	6.95 pesos 0.47
37 weeks	9.00 s.0.63	30.14 2.17	7.10 pounds 0.52
38 weeks	9.08 0.59	30.63 2.83	7.20 p.m. 0.43 p.m.
39 weeks	9.21 p.m. 0.59 p.m.	31.34 S.3.12	7.34 p.m. 0.53 p.m.
40 weeks	9.28 pence 0.50	31.49 2.79	7.40 p.m. 0.53 p.m.