Fetus Growth Charts
Fetus Measurement Growth Calculators
BPD - OFD - HC | Femur and Humerus (FL HL) | Abdominal Circumference (AC)
Fetal Measurement Growth Charts
After the first trimester of pregnancy a multiparameter assessment of gestational age is advocated. This should include at least two fetal measurements (usually biparietal diameter (BPD) and femur length (FL)) plus a consideration of additional parameters such as head circumference (HC), occipitofrontal diameter (OFD), abdominal circumference (AC) and humerus length (HL).
Measurements in the beam axis are more accurate than those made across the axis. Despite this, some measurements (e.g. Crown-Rump Length (CRL) and femur length) should be measured across the axis.
The earliest measurement of gestational age taken in pregnancy should usually be accepted as the definitive assessment, subsequent examinations reflecting only fetal growth in the intervening period. If measurements taken after the first trimester are within one week of the gestational assessment taken from menstrual dating then the ultrasound assessment of gestational age confirms the menstrual dates. If the ultrasound measurements are in agreement and differ from menstrual dates by more than one week prior to 20 weeks a new estimated due date should be calculated and recorded. The reduced accuracy of prediction of gestational age after 20 weeks must be appreciated.
At any gestation, if the ultrasound fetal measurements of each parameter are not in agreement, the reason for this difference should be evaluated. This is preferable to just averaging all values to arrive at an estimated gestational age.
The wide normal range of BPD in late pregnancy must be appreciated. It is not expected that BPD be used to assess gestation late in pregnancy. The values from 33 weeks are intended to predict the growth in fetal head size from a known gestation.
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Fetal Measurements = Weeks Calculator
|It is common to make at least 2 and often 4 or 5 measurements to estimate gestational age. |
In most cases, BPD [Biparietal diameter], HC [Head circumference], AC [Abdominal circumference] and FL [Femur length] are used.
Since all of these measurements are strongly related to gestational age, it is not usually important how they are combined. Normal +/- deviations are shown in (brackets) in the chart below.
No formula for estimating the fetal 'birth weight' has achieved an accuracy which enables us to recommend its use. It should be noted that errors of about 10% are reported and that even at this level of accuracy it is disappointing. It is suggested that there may be an improvement in accuracy of about 5% in using three rather than two parameters.
Estimated fetal weight calculator
Doing an ultrasound to estimate fetal weight near term is a very common practice, one still employed by many OBs, especially with large mothers. However, research clearly shows that this is a very questionable practice. The accuracy rate is very low, many women are pressured into interventions that do more harm than good, and even the mere PREDICTION of macrosomia (large baby) alters the way physicians perceive and treat labor.
A number of studies have questioned the use of ultrasound for estimated fetal birth weight. Given its inaccuracy and resulting interventions, this does NOT seem to be a justifiable use of the technology unless co-existing conditions like diabetes are present (even then, some research questions its use). However, it does remain common despite the research against it.
Fetal Growth Percentile Calculator:
Percentile Example: Out of 100 babies, a reading of forty percent (this is the percentile value) indicates that the baby is smaller than sixty other babies and larger than forty other babies. The mean or average is fifty percent. A value that reads below 50% indicates that the measurement is lower than the average. Thus, a value that is above 50% indicates that the measurement is above average.
A fetus is considered normal if they are between 10th and 90th percentile.
Estimated Fetal Weight Percentile Chart
Fetal Growth Percentile Charts:
BIPARIETAL DIAMETER AND HEAD CIRCUMFERENCE
|The BPD and OFD are measured on a transverse axial section of the fetal head which includes the falx cerebri anteriorly and posteriorly, the cavum septum pellucidum anteriorly in the midline and the thalami. The BPD is measured from the outer edge of the nearer parietal bone to the inner edge of the more distant parietal bone. The OFD is measured perpendicular to the BPD.|
The long bones are measured with the bone across the beam axis. The strong acoustic shadow behind the femoral or humeral shaft and the visualisation of both cartilaginous ends indicates that the image plane is on the longest axis and is the optimal measurement plane. The calipers are placed along the diaphyseal shaft excluding the epiphysis.
FEMUR AND HUMERUS LENGTH
These measurements are more appropriately used in the assessment of fetal growth, particularly in the second half of the pregnancy, than in the assessment of gestational age. It is, however, an appropriate measurement in the second trimester to demonstrate normal fetal proportions.
The abdominal circumference is measured at the level of the liver and stomach, including the left portal vein at the umbilical region.
Ultrasonic Fetal Measurement Standards
|If we assume a fetus is growing normally, biometric measurements are determined by gestational age, and we can estimate the gestational age and thus the due date. When the date of the last menses preceding conception is known, it is usually a more accurate estimate (+/- 5 days) of EDC|
When using ultrasound to estimate gestational age, remember that we are assuming the fetus is growing normally. Conditions which alter fetal growth will make the estimates less reliable. Although many embryonic and fetal structures can be measured, only a few measurements are easy and repeatable enough for widespread use.
The most common are:
The first element to be measurable is the gestation sac of the early pregnancy. The gestational sac is measured in three dimensions, and the average, the Mean Sac Diameter (MSD) used for estimating gestational age. It is useful between 5 and 8 menstrual weeks with accuracy of +/- 3 days . As a rough rule of thumb, the MSD + 30 = Menstrual Age in days.
Embryonic Crown-Rump Length:
The length of the embryo on the longest axis (excluding the yolk sac) constitutes the crown-rump length. This is among the best documented parameters to date the embryo, with accuracy of +/- 3-5 days. As a rough rule of thumb, the CRL + 6.5 = Menstrual Age in Weeks.
Biparietal diameter (BPD):
The transverse width of the head at it's widest. We measure from the the leading edge to leading edge of the bones, because this leading interface is most distinct. Since the head is oval, the error induced by small errors in positioning is small, making for a repeatable, robust measure.
Head size is determined largely by brain growth which is relatively independent of nutritional (maternal/placental insufficiency) growth retarding processes, and head growth is often relatively "spared" in such growth retardation.
The BPD best used after 12 weeks.
The femur length is a repeatable measurement with accuracy similar to the BPD. It is effected by skeletal dysplasias, but since these are rare, it is a reliable measurement which confirms measurements of the head. It is best measured after 14 weeks.
It is common to make at least 2 and often 4-5 measurements to estimate gestational age. In most cases, BPD, Head Circumference, Femur length, and Abdominal circumference are used.
Since all of these measurements are strongly related to gestational age, it is not usually important how they are combined. Most modern ultrasound machines include computerized biometric analysis programs used to easily calculate your Estimated Due Date or EDD or EDC.
Ultrasound Fetal Measurement Standards Chart
NOTE: +/- Standard deviations shown in (brackets). Measurements are for completed weeks.
Crown-Rump Length Measurements
How many scans should I have?
|As a practical matter, ultrasound scanning has proven to be so popular with patients and also their obstetricians, that almost everyone receiving regular prenatal care ends up with at least one scan anyway. The total number of scans will vary depending on whether a previous scan has detected certain abnormalities that require follow-up assessment.|
There is no hard and fast rule for the number of scans you should have during pregnancy.
Examples of ultrasonography you may see used during your pregnancy.
Ultrasound information :- Who, Why, When?
What happens during an ultrasound examination?
Can the scan show the gender of my baby?
Examples of ultrasonography you may see used during your pregnancy.
Week By Week Pregnancy Progress Calendar
Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7
Week 8 Week 9 Week 10 Week 11 Week 12 Week 13
Week 14 Week 15 Week 16 Week 17 Week 18 Week 19 Week 20
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Week 27 Week 28 Week 29 Week 30 Week 31 Week 32 Week 33
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