## What is the Hadlock formula?

Formula C of Hadlock et al [Hadlock C; log(10) BW = 1.335 – 0.0034(abdominal circumference [AC])(femur length [FL]) + 0.0316(biparietal diameter) + 0.0457(AC) + 0.1623(FL); Am J Obstet Gynecol 1985; 151:333-337] had the best performance according to the bias and precision method.

The accuracy of any ultrasonic fetal weight formula is dependent on its 95% confidence limit. For example, one of the more popular formulas is the Hadlock HC/AC/FL where the 95% confidence limit is ± 15% and so it is expected that 95% of actual birth weights will be within ± 15% of the predicted birth weight.

Objectives. Estimated fetal weight (EFW) helps inform clinical decision making in patients with preterm premature rupture of membranes (PPROM). The Hadlock IV formula is the most commonly used calculation of EFW using biparietal diameter, head circumference, abdominal circumference, and femur length.

### How is fetal size calculated?

Fetal length Calculator. Fetal length in centimeters = 6.18 + 0.59 x femur length in millimeters. Vintzileos AM, Campbell, et al. The ultrasound femur length as a predictor of fetal length.

Crown-rump length (CRL) is an ultrasound measurement that is used during pregnancy. The baby is measured, in centimeters, from the top of their head (crown) to the bottom of their buttocks (rump).

How accurate is the weight of baby in ultrasound?

2. Ultrasound is not very reliable for estimating fetal weight near term. For a 9-pound baby, an ultrasound’s predictive accuracy is typically 15 to 20 percent off. Which means we may over- or underestimate by more than a pound.

The Hadlock formula uses HC, AC, and FL to calculate the EFW. In our study, male and female fetuses differed in body composition with different indices for male and female fetuses. The Hadlock formula could therefore be improved by adjusting for fetal sex as previously suggested by others [8, 30–33].

What is the normal HC at 20 weeks?

Calculating estimated fetal weight (EFW)

Gestational Age (Weeks) BPD Head Circumference
19 weeks 46 162
20 weeks 49 175
21 weeks 52 187
22 weeks 55 198

How do you calculate CRL?

Gestational age (in days) = 8.052 * √(CRL * 1.037) + 23.73 , where: CRL is given in millimeters (mm)….How to calculate gestational age with crown-rump length?

CRL (in mm) Gestational age (weeks+days)
15 7 + 6
20 8 + 4
25 9 + 2
30 9 + 6

### How is CRL calculated in USG?

Crown-rump length (CRL) is an ultrasound measurement that is used during pregnancy. The baby is measured, in centimeters, from the top of their head (crown) to the bottom of their buttocks (rump). 1﻿ The limbs and yolk sac are not included in the measurement.