Can the biparietal diameter and femur length be used to determine fetal weight?

Mar 05, 2025 Source: Cainiu Health

Dr. Zhang Lu

Introduction

Under normal circumstances, the biparietal diameter (BPD) and femur length (FL) can serve as reference indicators for estimating fetal weight. During prenatal ultrasound examinations, doctors measure multiple parameters including BPD and FL, and use calculation formulas to estimate the fetal weight. These formulas incorporate various indicators such as gestational age, abdominal circumference, and head circumference, providing a relatively accurate prediction of fetal weight.

Generally, the biparietal diameter (BPD) and femur length (FL) can serve as reference indicators for estimating fetal weight. The detailed analysis is as follows:

During prenatal ultrasound examinations, doctors measure multiple parameters including the biparietal diameter and femur length, and use calculation formulas to estimate fetal weight. These formulas incorporate various indicators such as gestational age, abdominal circumference, and head circumference, thereby providing a relatively accurate predicted value for fetal weight. Therefore, the biparietal diameter and femur length can serve as one of the reference indicators for assessing fetal weight.

However, fetal weight estimation is a relatively complex process. In addition to the biparietal diameter and femur length, it is necessary to perform a comprehensive evaluation by combining factors such as the mother's uterine height, abdominal circumference, fetal development status, and gestational age. Moreover, fetal weight estimation can also be influenced by multiple factors such as fetal position, amniotic fluid volume, and placental position, so some degree of error is inevitable.

Pregnant women are advised to attend regular prenatal check-ups at the hospital to stay informed about their own health status and fetal development in a timely manner.

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What is the standard biparietal diameter?

Under normal circumstances, the standard values for the fetal biparietal diameter (BPD) vary according to gestational age. During pregnancy, the normal range for fetal biparietal diameter is approximately as follows: 20 mm at 12 weeks gestation, 34 mm at 16 weeks gestation, 59 mm at 24 weeks gestation, 70 mm at 28 weeks gestation, 79 mm at 32 weeks gestation, and 87 mm at 36 weeks gestation.

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What does persistent occiput transverse position dystocia mean?

In general, persistent transverse occipital dystocia refers to a condition during childbirth where the fetal head engages in the transverse occipital position, and during descent, the fetal枕骨 (occiput) persistently fails to rotate forward, remaining laterally positioned within the mother's pelvis until late stages of labor, thereby causing difficulty in delivery. It is advisable to maintain a balanced diet during pregnancy, control fetal weight gain, avoid excessive intake of high-calorie and high-fat foods, and prevent fetal macrosomia.

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What are the standard biparietal diameter and femur length at 27 weeks?

At 27 weeks, the standard biparietal diameter of a fetus is approximately 6.98 cm, and the standard femur length is around 5.10 cm. These two measurements are important indicators for assessing fetal head and lower limb development. If the examination results significantly deviate from the standard values or show abnormal growth, it is recommended to seek medical advice promptly for further evaluation. The biparietal diameter reflects the developmental status of the fetal head.

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Does a normal biparietal diameter with slightly small head circumference have any impact?

In general, whether a normal biparietal diameter with a slightly small head circumference has any impact needs to be comprehensively analyzed based on specific data and gestational age. Pregnant women should maintain a balanced diet, consume adequate high-quality protein and DHA, follow a regular作息 (daily routine), avoid fatigue, stay in good spirits, and strictly adhere to medical advice for prenatal checkups and related adjustments.