Enter gestational age and estimated fetal weight to compare the value with a selected reference. This page is informational and does not diagnose fetal health.
Use the calculator to see where a value falls in a reference, not to make medical decisions.
Enter the pregnancy week, days, and the estimated fetal weight from the ultrasound report. Before 22 weeks, the form switches from estimated fetal weight to fetal biometry measurements.
A percentile describes where the entered value sits within the selected reference. It is not a normal or abnormal judgment, and it should not replace clinical review.
EFW means estimated fetal weight. It is calculated from ultrasound measurements and can vary by formula, equipment, fetal position, and timing.
These answers explain common interpretation limits and data choices visible on this page.
No. The result is a reference percentile only. It does not diagnose growth restriction, macrosomia, placental function, or future outcome.
Use the estimated fetal weight, often written as EFW, from the ultrasound report. Do not enter maternal weight or a predicted birth weight from another app.
Use the reference your clinician or ultrasound report expects when one is specified. If you compare another source, read it as a separate reference shown as selected.
You can change the data source, but each result is shown against the selected reference and study population. Datasets are not mixed or combined.
That source is based on birth-weight statistics by gestational age. The page marks it separately when an EFW input is compared with a birth-weight reference.
Before 22 weeks, the calculator uses WHO fetal biometry references for measurements such as head circumference or abdominal circumference.
No. The calculator is designed so pregnancy week, estimated fetal weight, sex selection, and result values are not stored as server-side records.
Ask your clinician to interpret the value together with the full ultrasound report, exam history, and local clinical guidance.
Each source is based on a different study and population, so the calculator displays the selected reference as-is and does not mix or combine datasets.
The World Health Organization fetal growth charts were published in 2017 in PLOS Medicine.
The charts were produced by an international research team working with the World Health Organization. The published article lists Torvid Kiserud, Gilda Piaggio, Guillermo Carroli, Mariana Widmer, José Carvalho, Lisa Neerup Jensen, Daniel Giordano, José Guilherme Cecatti, Hany Abdel Aleem, Sameera A. Talegawkar, and additional collaborators.
The work was funded by the UNDP/UNFPA/UNICEF/WHO/World Bank Special Programme of Research, Development and Research Training in Human Reproduction, Department of Reproductive Health and Research, World Health Organization.
Source: https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1002220
This source is credible because it was published in a peer-reviewed medical journal, was produced with World Health Organization involvement, and used a prospective multinational study design. The publication describes the study population, pregnancy risk criteria, gestational-age confirmation method, ultrasound schedule, and statistical approach.
The study was designed to create fetal growth references from low-risk singleton pregnancies rather than from a mixed clinical population with unknown risk factors.
The study followed low-risk singleton pregnancies from 10 countries:
Participants were women of high or middle socioeconomic status without known environmental constraints on fetal growth. Gestational age was checked using crown-rump length measured at 8 to 13 weeks. The final study population included 1,387 participants.
This source is based on ultrasound estimated fetal weight and fetal biometric measurements, not direct fetal weighing. Estimated fetal weight is calculated before birth from ultrasound measurements, so values can vary with measurement quality, fetal position, equipment, and the formula used.
This was a multinational prospective longitudinal ultrasound study. Participants had scheduled assessments during pregnancy, including repeated ultrasound examinations. The researchers collected common fetal biometric measurements and used them to produce fetal growth charts, including estimated fetal weight.
Estimated fetal weight is not directly weighed before birth. It is calculated from ultrasound measurements, commonly including head, abdomen, and femur measurements. The WHO paper reports percentile charts for estimated fetal weight and several ultrasound biometric measurements.
The WHO chart shows how an estimated fetal weight compares with values from a multinational low-risk singleton pregnancy reference group.
For example, a 50th percentile value means that the estimate is near the middle of the reference distribution for that gestational age. A lower or higher percentile means the estimate is lower or higher relative to this reference group, not automatically abnormal.
Use the WHO chart as a broad international comparison point. It can be especially helpful when no high-quality local reference is available.
The chart should be interpreted as a reference position, not a clinical conclusion. A percentile result needs context: gestational dating accuracy, ultrasound measurement quality, interval growth, maternal and fetal history, and the clinician's assessment all matter.
This source should not be used by itself to diagnose fetal growth restriction, macrosomia, placental insufficiency, or pregnancy risk. It provides a reference comparison only. Clinical interpretation requires medical history, ultrasound quality, gestational dating, growth trend, and clinician assessment.
The WHO fetal growth chart is a strong international reference built from a prospective, multinational, low-risk pregnancy cohort. Its main value is broad comparability. Its main limitation is that an international average reference may not fit every local population or every individual pregnancy.
The INTERGROWTH-21st Hadlock estimated fetal weight standard was published in 2020 in Ultrasound in Obstetrics & Gynecology. The broader INTERGROWTH-21st project was conducted between 2009 and 2014.
The 2020 Hadlock estimated fetal weight update was authored by J. Stirnemann, L. J. Salomon, and A. T. Papageorghiou. It belongs to the INTERGROWTH-21st family of standards and tools.
Source: https://intergrowth21.com/tools-resources/fetal-growth
This source is credible because it belongs to the INTERGROWTH-21st family of standards, which was built through a coordinated international research program with defined study sites, protocols, and quality-control procedures. The 2020 estimated fetal weight update was published in a peer-reviewed ultrasound journal and clearly states the formula used for the updated charts.
Its main credibility strength is methodological consistency: the reference is tied to a known international project and uses a specified Hadlock three-parameter estimated fetal weight method.
The broader INTERGROWTH-21st project was a multi-centre, multi-ethnic, population-based project conducted in eight urban areas:
The project focused on growth, health, nutrition, and neurodevelopment from early pregnancy through early childhood. The fetal growth standards were built from carefully selected populations intended to support international prescriptive standards.
This source is based on ultrasound estimated fetal weight, not direct fetal weighing. The 2020 charts use the Hadlock estimated fetal weight formula based on abdominal circumference, head circumference, and femur length.
Because estimated fetal weight is formula-based, the percentile result depends on both the ultrasound measurements and the selected formula.
The 2020 estimated fetal weight charts updated the earlier EFW approach to use the Hadlock formula with three ultrasound parameters:
The INTERGROWTH-21st resource page states that the 2020 updated charts are the recommended INTERGROWTH-21st charts for estimated fetal weight.
This standard compares an estimated fetal weight with an international INTERGROWTH-21st reference framework using the Hadlock three-parameter EFW formula.
The result is a percentile or z-score position within that reference. It describes relative size compared with the selected standard. It does not directly measure health, placental function, or future outcome.
Use this source as an international standard-based comparison. It is especially useful when a consistent global framework is desired.
Different standards may produce different percentile positions because they are built from different populations, formulas, gestational-age handling, and statistical approaches. A difference between INTERGROWTH-21st and another source should be treated as a reason to understand the source context, not as proof that one result is clinically wrong.
This source should not be used by itself to diagnose fetal growth restriction, macrosomia, placental insufficiency, or pregnancy risk. It should also not be mixed or combined with other reference charts. It provides a standard-based comparison, and clinical interpretation requires gestational dating, ultrasound quality, growth trend, and medical context.
The INTERGROWTH-21st Hadlock EFW standard is a respected international comparison source. Its strength is a consistent multi-country framework and updated Hadlock-based EFW method. Its limitation is that a global standard may not capture every local population pattern or individual clinical situation.
The Japanese ultrasound fetal biometry reference was published in 2025 in Scientific Reports.
The study was authored by Sumito Nagasaki, Keisuke Ishii, Yoshitaka Murakami, Anna Tsutsui, Nobuhiro Hidaka, Hironori Takahashi, Kiyotake Ichizuka, Kei Miyakoshi, Kiyonori Miura, Susumu Miyashita, Yoshimasa Kamei, Masahiko Nakata, and the Study Group on New Reference Values for Fetal Biometry in Japan.
Source: https://www.nature.com/articles/s41598-025-14508-9
This source is credible because it was published in a peer-reviewed scientific journal, used a prospective research protocol, and was designed specifically to reassess fetal biometry reference values in Japan. The study describes the population, ultrasound measurements, estimated fetal weight formulas, and statistical method used to build gestational-age-specific values.
Its credibility is strongest for Japanese fetal biometry patterns because the study was designed around a Japan-specific population and measurement context.
The study included singleton pregnancies receiving prenatal checkups at obstetric facilities across Japan. It was designed as a cross-sectional prospective study using a research-specific protocol to improve ultrasound data quality.
The authors state that the work was motivated by changes in Japanese birthweight trends, advances in ultrasound technology, and the need to reassess older Japanese fetal biometry charts.
This source is based on ultrasound fetal biometric measurements and estimated fetal weight, not direct fetal weighing. Estimated fetal weight was calculated using both the Shinozuka formula and the Hadlock-3 formula.
Because different formulas can produce different estimated fetal weights, the formula context is part of how the percentile should be interpreted.
During routine prenatal care, the study recorded ultrasound measurements including:
Estimated fetal weight was calculated using both the Shinozuka formula, commonly used in Japan, and the Hadlock-3 formula, widely used internationally. The authors then developed gestational-age-specific reference values using best-fitted fractional polynomial regression.
This source describes fetal ultrasound biometric measurements and estimated fetal weight patterns in a Japanese population.
The study found that fetal biometry values in the Japanese population were generally smaller than international standards and also smaller than values reported from other Asian references. This supports the idea that population-specific references can matter when assessing fetal size.
Use this source as a Japan-specific ultrasound reference. A percentile based on this source means the measurement is being compared with the Japanese study population at a similar gestational age.
It should not be interpreted as a general "Asian" reference. The authors specifically describe the Japanese population and compare it with international and other Asian studies.
This source should not be used by itself to diagnose fetal growth restriction, macrosomia, placental insufficiency, or pregnancy risk. It should also not be generalized to all Asian populations. It provides a Japan-specific reference comparison, and clinical interpretation requires gestational dating, ultrasound quality, growth trend, and medical context.
The Japan 2025 reference is valuable because it is recent, prospective, and population-specific. Its main strength is relevance to Japanese fetal biometry patterns. Its main limitation is that it should not be generalized beyond the population and methods used to build it.
The Korean birth-weight reference was published in 2016 in the Journal of Korean Medical Science.
The study was conducted by Korean researchers using Korean Statistical Information Service birth data. The article lists Jae Kwan Lee, Hyun-Lim Jang, Bo Hye Kang, Kyung-Sook Shim, Yun Sil Chang, Chong-Woo Bae, and So-Hee Chung among the authors.
Source: https://jkms.org/DOIx.php?id=10.3346%2Fjkms.2016.31.6.939
This source is credible because it was published in a peer-reviewed medical journal and used a very large national Korean birth dataset. The study describes its inclusion and exclusion criteria, gestational-age range, sex and plurality handling, and statistical method for addressing known error patterns in administrative data.
Its credibility is strongest as a Korean population birth-weight reference because it is based on more than 1.4 million births after exclusions.
The study used Korean Statistical Information Service data for all newborns from January 2010 through December 2012.
The raw dataset included 1,425,986 newborns. After excluding records with unknown birth weight, unknown gestational age, gestational age below 22 weeks, or gestational age above 42 weeks, the study analyzed 1,422,890 births.
The reference considered:
This source is based on measured birth weight after delivery, not antenatal ultrasound estimated fetal weight. Birth weight is a direct post-delivery measurement, while estimated fetal weight is a prenatal calculation from ultrasound measurements.
This difference is important because a birth-weight percentile and an ultrasound estimated fetal weight percentile are related comparisons, but they are not the same type of measurement.
The study analyzed birth weight by completed gestational week. Gestational age was defined as the interval between the first day of the mother's last menstrual period and the delivery date, expressed in completed weeks. Birth weight was measured to the nearest 10 grams.
The authors identified error patterns in the large national dataset, including a double-humped distribution around 28 to 32 weeks. They used a finite Gaussian mixture model to remove estimated error data before building the percentile distributions.
This source shows Korean newborn birth-weight percentiles by gestational age, sex, and plurality. It is a birth-weight reference, not an antenatal ultrasound estimated fetal weight reference.
This distinction matters. Birth weight is measured after delivery. Estimated fetal weight is calculated before delivery from ultrasound measurements. They are related but not identical.
Use this source as a Korean population birth-weight comparison. It can help show how a weight value compares with Korean newborn birth-weight distributions at the same completed gestational week.
When comparing an ultrasound estimated fetal weight with this source, interpret the result cautiously. The comparison is between a prenatal estimate and a birth-weight distribution, not between two identical measurement types.
This source should not be used by itself to diagnose fetal growth restriction, macrosomia, placental insufficiency, or pregnancy risk. It should not be treated as an ultrasound fetal growth standard because it is based on birth weights after delivery. Clinical interpretation requires pregnancy context, timing of delivery, gestational dating, and clinician assessment.
The Korea JKMS 2016 reference is valuable because it is based on a very large national Korean birth dataset and separates results by gestational age, sex, and plurality. Its main limitation is that it is based on birth weight, so it must be interpreted differently from ultrasound estimated fetal weight references.
The NICHD Fetal Growth Study racial and ethnic fetal growth standards were published in 2015 in the American Journal of Obstetrics and Gynecology.
The study was conducted by investigators associated with the Eunice Kennedy Shriver National Institute of Child Health and Human Development Fetal Growth Studies. The published article lists Germaine M. Buck Louis, Jagteshwar Grewal, Paul S. Albert, Anthony Sciscione, Deborah A. Wing, William A. Grobman, Roger B. Newman, Ronald Wapner, Mary E. D'Alton, Daniel Skupski, Michael P. Nageotte, Angela C. Ranzini, John Owen, Edward K. Chien, Sabrina Craigo, Mary L. Hediger, Sungduk Kim, Cuilin Zhang, and Katherine L. Grantz.
Source: https://doi.org/10.1016/j.ajog.2015.08.032
This source is credible because it was published in a peer-reviewed obstetrics journal and came from the Eunice Kennedy Shriver National Institute of Child Health and Human Development Fetal Growth Studies. It used a prospective multicenter design, low-risk pregnancy screening, repeated ultrasound assessment, and documented statistical modeling.
Its credibility is especially strong for explaining why fetal growth references may differ across defined United States study groups.
The study recruited 2,334 healthy women with low-risk singleton pregnancies from 12 community and perinatal centers in the United States between July 2009 and January 2013.
The cohort included four self-identified groups:
Participants were screened early in pregnancy for health status and low-risk characteristics. The published abstract reports that 1,737 fetuses continued to meet the low-risk standard at birth and were included in the final standards.
This source is based on ultrasound estimated fetal weight and fetal biometric measurements, not direct fetal weighing. Estimated fetal weight is calculated from ultrasound measurements, so values can vary with measurement quality, fetal position, equipment, and formula choice.
Participants were followed prospectively with longitudinal fetal measurements. Women were assigned among four ultrasound schedules, and interviews, anthropometric assessments, and medical record abstraction were performed.
The researchers estimated group-specific fetal growth curves using linear mixed models with cubic splines. They calculated estimated fetal weight and biometric parameter percentiles for each gestational week.
The NICHD standards show how estimated fetal weight differs across the four self-identified United States study groups. The study found statistically significant differences in estimated fetal weight after 20 weeks.
The study group labels describe the source population used to build each chart. They should not be read as a biological rule, an identity judgment, or a clinical instruction.
Use the NICHD source as a United States study-group-specific comparison. It can help explain why a single pooled chart may classify measurements differently across populations.
The percentile result means "relative to this NICHD study group at this gestational age." It does not mean that the selected study group is medically required for a specific user, and it does not diagnose a fetal growth condition.
This source should not be used by itself to diagnose fetal growth restriction, macrosomia, placental insufficiency, or pregnancy risk. It should not be used to assign personal identity or biological meaning to a person. The study-group labels describe how the source population was analyzed, and clinical interpretation requires broader medical context.
The NICHD Fetal Growth Study is valuable because it was prospective, multicenter, and designed to examine fetal growth differences across self-identified United States study groups. Its main limitation is that the group-specific charts require careful wording and should not be treated as automatic personal classification or diagnosis.