⭐Fetal weight: calculation and tables

Fonte: shutterstock

Fetal weight

Pregnancy is, for every woman, a magical period, but also full of worries and fears, especially if it is the first. You would like to know, every minute (indeed, second!) If your child is well, if he has grown up, how much does it weight. This is what they are for fetal weight gauges.

But let's find out better why the fetal weight in pregnancy it is so important and how you can measure it even at home.

Why know the weight of the fetus in pregnancy
Video: Fetus weight, how to calculate it
Male fetus weight table
Weight table of the female fetus
Calculation of fetal weight
Calculation of fetal weight Hadlock and Shepard
Growth percentages
Fetal weight from the 33rd to the 38th week of pregnancy
Fetal weight, growth retardation

Why know the weight of the fetus in pregnancy

Know the weight of the fetus in the various weeks of pregnancy, in addition to informing the mother about the growth of her baby, it is used by gynecologists for monitor its growth and to understand if everything is normal. As every mother knows well, during the ultrasound, the gynecologist takes some measurements of the fetus (the abdominal circumference, the biparietal diameter, for example) and thanks to these he is able to estimate the approximate weight. We speak of 'approximate', since, in reality, the actual weight of the baby can only be verified after its birth.

With the calculation of the weight of the fetus, however, the gynecologist will be able to verify whether or not those measures fall within the medical parameters. In the first months of pregnancyTherefore, knowing the fetal weight is useful for specialists to understand if everything is proceeding according to the norm or to identify, in the worst case, more or less serious anomalies (genetic malformations, for example). Towards the end of gestationon the other hand, the estimate of the weight of the fetus allows doctors to identify which birth to choose (natural or caesarean) and psychologically helps the mother to prepare for the stage of labor.

Video: Fetus weight, how to calculate it

Male fetus weight table

Below is a reference table for the fetal weight of boys that emerged from the study entitled The World Health Organization Fetal Growth Charts: A Multinational Longitudinal Study of Ultrasound Biometric Measurements and Estimated Fetal Weight, published in PLOS Medicine

Male fetal weight reference table

Weight table of the female fetus

Below is a reference table for the fetal weight of girls that emerged from the study entitled The World Health Organization Fetal Growth Charts: A Multinational Longitudinal Study of Ultrasound Biometric Measurements and Estimated Fetal Weight, published in PLOS Medicine

Female fetal weight reference table

Calculation of fetal weight

Il weight of the fetus in pregnancy it is calculated thanks to some specific measures:

il biparietal diameter (Bpd),
la abdominal circumference (Ac),
in some cases, even the head circumference (Hc) and femur length (Fl).

Once you are aware of these measurements, you need a electronic calculator in order to learn about the fetal weight.

When the gynecologist does an ultrasound to a pregnant woman, he asks for help from the machinery, but, in reality, even mothers and fathers can calculate the weight of their baby at home, relying on secure online calculators.

Calculation of fetal weight Hadlock and Shepard

There are numerous formulas for calculating the weight of the fetus, but the most famous are two:

Hadlock: this formula includes, in the calculation of the fetal weight all 4 parameters mentioned above (Bdp, Ac, Hc, Fl)
Shepherd: this formula takes into account only biparietal diameter and abdominal circumference.

There are also other formulas, such as that of Campbell e Wilkin which, however, is less precise since it takes into consideration only the abdominal circumference of the fetus.

As previously explained, the values estimated by the above formulas are then compared to some growth charts, that is, at average values that are fundamental to understand if the fetus is growing correctly. It is about tables showing trends by percentiles and which, at least initially, are not very easy to read.

Read also: How to understand the sex of the baby from the ultrasound

Growth percentages

Each child has their own growth curve which is calculated in percentiles, in fact. All those children who have a range of growth are considered normal between the 25th and 75th percentile. Growth, in fact, may depend on genetic, constitutional (a child with two tall parents will be more likely to be tall), hormonal, food factors. The percentile value is taken into consideration during pregnancy and also in the first years of the baby's life.

Fetal weight from the 33rd to the 38th week of pregnancy

Le last weeks of pregnancy are those in which the weight of the fetus is decisive. Should there be a decrease or arrest in the growth of the baby, the gynecologist could also opt for an early birth. On average, however, if in the previous months, the pregnancy did not show particular anomalies, from the 33rd to the 38th week the child will continue to grow regularly, according to the reference tables. Here is how much a fetus should weigh between the 33rd and 38th week:

33rd week: the fetus measures 42 centimeters and weighs about 1700 grams
34th week: The fetus is 43 centimeters long and weighs approximately 1900 grams
Week 35: The fetus is 46 centimeters long and weighs approximately 2,140 pounds
36th week: The fetus is 46 centimeters long and weighs approximately 2,380 grams
37th week: the baby measures about 47 centimeters and its weight is around 2.600 grams
38th week: the baby measures approximately 48 centimeters and weighs approximately 2,800 grams

Fetal weight, growth retardation

Il fetal weight, as previously mentioned, it is essential to monitor the baby's growth in the belly and to identify, possibly, developmental delays. Fetal growth retardation occurs when the weight of the fetus is less than the 10th percentile. It is not always a pathology (the child can be small also because the parents are particularly small), but it is the task of the prenatal diagnosis understand the reasons for this slow growth.

Here are some of the causes that could generate fetal growth retardation: