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Babies start growing from early pregnancy. Ultrasound scans are done at regular intervals during pregnancy and help determine the approximate weight and length of the baby. The growth of the foetus in the womb causes the increase in the size of the bump too.
Foetal Weight Chart
The table below shows the average increase in weight of the foetus on a week by week basis. The numbers are only averages, and the actual weight and length of the foetus may vary significantly.
The doctor will be concerned only if the baby weighs two weeks less or more than what he should weigh during a particular pregnancy week. These are general guidelines and the baby’s weight may not be an exact match. However, this should not be a cause for worry.
Along with the weight the doctor also keeps a record of the foetal length
|Pregnancy Week||Average Weight in gms|
Foetal Length Chart
This chart is a rough guide of the foetal length on a week by week basis. The length is measured from the crown till the heel from the 20th week onwards.
|Pregnancy Week||Average Length in cms|
Ultrasonic Foetal Measurement Standards
The gestational age chart is used to determine the biometric measurements and determine if the foetus growth is normal. If one is able to provide the date of the last menses before conception, it gives a much better estimate of EDC, which is the estimated date of confinement (also known as Expected Date of Delivery). The EDC can be estimated to +/- 5 days.
The method of using ultrasound to estimate the gestational age is done under the assumption that the baby is growing normally and as per the foetus weight chart in kg. If any condition alters the growth of the foetus, it will also make the estimate less reliable. The ultrasound method lets one measure a number of foetal and embryonic structures, but only a few of them are reliable and easy to carry out repeatedly. The ultrasound foetal measurements are done using various foetal graphs and calculators.
Estimated Foetal Weight Calculator
The foetal weight calculator lets you calculate the percentile of the foetal weight as well as the estimated foetal weight at the time of delivery. The inputs that you need to enter are the gestational age, biparietal diameter, humerus, head circumference, femur length, and the abdominal circumference. The calculator then calculates the percentile for each factor as well as the estimated foetal weight at the time of delivery.
Suppose the foetus is in the 60th percentile for weight, at 30 weeks. This means that 60% of foetuses weigh the same or less than the baby at 30 weeks. This means that 40% of foetuses weigh more than the baby at 30 weeks.
It is a common practise to opt for an ultrasound to estimate the weight of the foetus near the end of pregnancy. The accuracy rate of this method is very low and the calculated weight may lead to changes in the way the mother and the physician may perceive the delivery. Therefore, the method has been questioned in medical circles, and is not recommended until there is a medical condition.
The foetal weight calculator calculates the foetal weight as well as the estimated foetal weight at the time of delivery as per ultrasound data using many formulas like Warsof, Shepard, Hadlock, Campbell and so on.
The calculation is carried out using the four basic parameters which are: head circumference (HC), biparietal diameter (BPD), abdominal circumference (AC) and femur length (FL).
The calculated foetal weights may be 16% plus or minus the average weight. The actual weight can be either higher or lower than 16%.
Around 68% of babies will be within the range of 1 standard deviation(SD), and 2 SD should encompass around 95% of the actual weight. However, about 5% of the babies will be either higher or lower than 2.5%, thus making this an inaccurate calculator of foetal weight.
Foetal Growth Percentile Calculator
The growth percentile calculator calculates how big or small the baby is from the average value. If the baby’s growth percentile is 40, this means that the baby is larger than 40 other babies who are the same age, and smaller than 60 babies of the same age. 50 is the average value and a value below 50 means that the baby’s growth is below the average value. A value above 50 means that the baby has an above average growth-rate.
A foetus that measures between the 10th and the 90th percentile, is considered normal .The foetal percentile growth calculator provides an estimate which may not be exact.
The different terms used in tracking or calculating growth of the foetus in the womb are briefed upon below for a better understanding:
Crown Rump Length
The embryonic crown rump length is a parameter that dates the embryo and estimates the fetus average length. It can be measured to an accuracy of +/- 3 to 5 days. The longest axis excluding the yolk sac is used to measure the length of the embryo. The menstrual age in weeks is calculated as the crown rump length plus 6.5. A similar method used is the crown heel length.
Biparietal Diameter and Head Circumference
The BPD or the Biparietal diameter is the transverse width of the head at the widest part. The measurement is done from one leading edge to the other leading edge of the bone on the opposite side, as it is the most distinct. The error in this measurement is not a lot as the oval shape of the head does not leave scope for a lot of mistakes. This makes it easy to use the method over and over again.
The size of the head is determined by the growth of the brain and does not take into account the nutritional growth or any retarding process.
Femur and Humerus Length
The femur length method is also reliable and can be repeated. Skeletal dysplasias tend to affect it but the condition is very rare. The measurement confirms the head measurement and the best value can be obtained after 14 weeks. To estimate the gestational age, at least 2 or sometimes even 4-5 measurements may be required.
Estimated Foetal Weight
BPD, FL and AC are also used to estimate the foetus average weight. There are a number of computer software and charts that help the doctor calculate the foetal weight. A number of formulae are also used and the one that is the best has a 15% margin error.
This is a measurement taken in the second half of the pregnancy and is used to assess the foetal growth. It is an approximate method and it is used to see if the growth proportions of the foetus are normal. It is measured at the level of the liver and the stomach along with the left portal vein at the umbilical region.
This is measured in early pregnancy and is measured in three dimensions. The ‘Mean Sac Diameter’ is the average that is used to estimate the gestational age. The method can be applied between the 5th and the 8th week and has an accuracy of +/- 3 days. The menstrual age in days is calculated as MSD+30.
The gestational sac surrounds the embryo and can be seen in the early ultrasound scans. The sac encloses the embryo as well as the amniotic fluid. It allows the doctor to measure the number of weeks of pregnancy and gives an accuracy of about 5 days.
This is a membranous sac and is attached to the embryo. The sac can be spotted between the embryo and the gestational sac. It offers nourishment to the embryo before the circulatory system and the placenta develops to give the foetus the required nourishment.
This is a mass of cell and can be seen before the embryo becomes visible. The rate of growth is approximately 1 mm a day and starts at the 6th week of the gestational age. It is used to date an early pregnancy and the method is to add the length of the foetal pole to 6 weeks. This method is also used to estimate the gestational week.
The gestational age is calculated in most cases by using BPD, femur length, head circumference, and abdominal circumference. It may not be very important to see how they are combined. The modern ultrasound machines have a computer biometric analysis program that calculates the estimated due date.
The doctor may conduct a multiparameter assessment of the gestational age after the first trimester of pregnancy. The basic ones are the biparietal diameter and the femur length. The other parameter such as occipitofrontal diameter, head circumference or humerus length are also considered.
The early measurement to calculate gestational age is usually taken as a definite assessment. There is a reduced accuracy after 20 weeks. The doctor would evaluate further if the ultrasound foetal measurement standard parameters are not in agreement at any time. This is done to average all the values to get an estimated gestational age.
These are the international standards of weight and length using guidelines from UK. The average weight and length of an Indian baby may be slightly less than the international standards.
The foetal growth chart is an important indicator of the progress of the pregnancy and the growth of the baby and any anomaly detected during the regular measurements is addressed by the doctor to see if intervention is necessary. It is advisable to go for all the mandatory checkups and scans during pregnancy to ensure that the charts are tracked correctly.