# Three fetal growth standards disagree on which fetuses are small

Bottleneck · id `maternal:bottleneck-fetal-growth-standard-choice` · Maternal & Newborn Atlas · release `c7fb95f1d15a7d13` (public)

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Browse, life stage: Pregnancy  
Browse, care area: The baby before birth  

## In plain language

Three major sets of fetal growth charts, one from the United States and two international, give different weights for a typical baby at 39 weeks and so flag different babies as small. There is no agreed single chart, and the effect of the choice on illness and death has not been compared.

## Technical summary

The 2018 expert review (PMID 29275821) compares the NICHD, INTERGROWTH-21st and a WHO study and reports different 50th percentile estimated fetal weights at 39 weeks, and says different percentages of small- and large-for-gestational-age fetuses will be identified. It lists the comparison of misclassification against morbidity and mortality as an important data gap and notes that cut points may need to be tighter (2.5th or 97.5th) or set in local populations. The SMFM definition of growth restriction uses a 10th percentile line set by a chart, so the choice matters for diagnosis.

## Claims, with the population each applies to

## Context: Fetuses of low-risk women in three longitudinal growth cohorts (NICHD, INTERGROWTH-21st, a WHO study), as compared in an expert review

Recipient: Fetal; Population: Fetuses of women with low-risk pregnancies in three recently completed longitudinal cohort studies that developed fetal growth charts, one in the United States and two international. The review compares the aims, sampling frames and analytic approaches.; Care setting: Not stated in the review abstract; Geography: United States (NICHD study) and international (INTERGROWTH-21st and the WHO study); Life stage: Pregnancy; Gestational age: Not reported; Postnatal age: Not reported; Follow-up: Not stated in the parts of the source that were read.

### An expert review compared three recently completed longitudinal cohort studies that built fetal growth charts: the NICHD Fetal Growth Studies in the United States and two international studies (INTERGROWTH-21st and a World Health Organization study). All three included low-risk women, yet the percentiles for fetal measures and estimated fetal weight varied between them. At 39 weeks the 50th percentile estimated fetal weight was 3502 g for white, 3330 g for Hispanic, 3263 g for Asian and 3256 g for Black women in the NICHD study, compared with 3186 g for INTERGROWTH and 3403 g for the WHO study. The review says that applying these standards to a clinical population will identify different percentages of small- and large-for-gestational-age fetuses, and that comparing misclassification of small and large fetuses in relation to illness and death under different criteria is an important data gap.

- Category: Description
- Evidence stage: Evidence synthesis
- Certainty: Certainty not assessed
- Applies to: Recipient: Fetal; Population: Fetuses of women with low-risk pregnancies in three recently completed longitudinal cohort studies that developed fetal growth charts, one in the United States and two international. The review compares the aims, sampling frames and analytic approaches.; Care setting: Not stated in the review abstract; Geography: United States (NICHD study) and international (INTERGROWTH-21st and the WHO study); Life stage: Pregnancy; Gestational age: Not reported; Postnatal age: Not reported; Follow-up: Not stated in the parts of the source that were read.
- Limitations: This is a narrative expert review by authors connected to the NICHD study (PubMed lists NIH intramural support), not a systematic review. The review names its third study the World Health Organization Multicentre Growth Reference Study; the abstract does not say whether that is the same publication as the WHO fetal growth charts paper in this atlas, so the two are not linked here. Only the abstract was read, and the figures are the review's own.
- Last checked: 2026-10-14
- Sources:
  1. Supports: Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study (Publication, edition PubMed record (abstract and bibliographic data) from NCBI E-utilities, retrieved 2026-10-14. The full text and the version of record were not read.) <https://doi.org/10.1016/j.ajog.2017.11.593>
     Locator: Abstract, sentence 1. Retrieved 2026-10-14T18:18:27Z. Source state: Current. Snapshot hash: fd5963be0dc6a68d10e4c9182534ffbe44918aff9de7eb9f4500341a687c9078.
     How it applies: PubMed abstract.
  2. Supports: Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study (Publication, edition PubMed record (abstract and bibliographic data) from NCBI E-utilities, retrieved 2026-10-14. The full text and the version of record were not read.) <https://doi.org/10.1016/j.ajog.2017.11.593>
     Locator: Abstract, sentence 2, fragment 1 of 2. Retrieved 2026-10-14T18:18:27Z. Source state: Current. Snapshot hash: fd5963be0dc6a68d10e4c9182534ffbe44918aff9de7eb9f4500341a687c9078.
     How it applies: PubMed abstract.
  3. Supports: Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study (Publication, edition PubMed record (abstract and bibliographic data) from NCBI E-utilities, retrieved 2026-10-14. The full text and the version of record were not read.) <https://doi.org/10.1016/j.ajog.2017.11.593>
     Locator: Abstract, sentence 2, fragment 2 of 2. Retrieved 2026-10-14T18:18:27Z. Source state: Current. Snapshot hash: fd5963be0dc6a68d10e4c9182534ffbe44918aff9de7eb9f4500341a687c9078.
     How it applies: PubMed abstract.
  4. Supports: Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study (Publication, edition PubMed record (abstract and bibliographic data) from NCBI E-utilities, retrieved 2026-10-14. The full text and the version of record were not read.) <https://doi.org/10.1016/j.ajog.2017.11.593>
     Locator: Abstract, sentence 11. Retrieved 2026-10-14T18:18:27Z. Source state: Current. Snapshot hash: fd5963be0dc6a68d10e4c9182534ffbe44918aff9de7eb9f4500341a687c9078.
     How it applies: PubMed abstract.
  5. Supports: Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study (Publication, edition PubMed record (abstract and bibliographic data) from NCBI E-utilities, retrieved 2026-10-14. The full text and the version of record were not read.) <https://doi.org/10.1016/j.ajog.2017.11.593>
     Locator: Abstract, sentence 12, fragment 1 of 3. Retrieved 2026-10-14T18:18:27Z. Source state: Current. Snapshot hash: fd5963be0dc6a68d10e4c9182534ffbe44918aff9de7eb9f4500341a687c9078.
     How it applies: PubMed abstract.
  6. Supports: Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study (Publication, edition PubMed record (abstract and bibliographic data) from NCBI E-utilities, retrieved 2026-10-14. The full text and the version of record were not read.) <https://doi.org/10.1016/j.ajog.2017.11.593>
     Locator: Abstract, sentence 12, fragment 2 of 3. Retrieved 2026-10-14T18:18:27Z. Source state: Current. Snapshot hash: fd5963be0dc6a68d10e4c9182534ffbe44918aff9de7eb9f4500341a687c9078.
     How it applies: PubMed abstract.
  7. Supports: Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study (Publication, edition PubMed record (abstract and bibliographic data) from NCBI E-utilities, retrieved 2026-10-14. The full text and the version of record were not read.) <https://doi.org/10.1016/j.ajog.2017.11.593>
     Locator: Abstract, sentence 12, fragment 3 of 3. Retrieved 2026-10-14T18:18:27Z. Source state: Current. Snapshot hash: fd5963be0dc6a68d10e4c9182534ffbe44918aff9de7eb9f4500341a687c9078.
     How it applies: PubMed abstract.
  8. Supports: Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study (Publication, edition PubMed record (abstract and bibliographic data) from NCBI E-utilities, retrieved 2026-10-14. The full text and the version of record were not read.) <https://doi.org/10.1016/j.ajog.2017.11.593>
     Locator: Abstract, sentence 13, fragment 1 of 2. Retrieved 2026-10-14T18:18:27Z. Source state: Current. Snapshot hash: fd5963be0dc6a68d10e4c9182534ffbe44918aff9de7eb9f4500341a687c9078.
     How it applies: PubMed abstract.
  9. Supports: Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study (Publication, edition PubMed record (abstract and bibliographic data) from NCBI E-utilities, retrieved 2026-10-14. The full text and the version of record were not read.) <https://doi.org/10.1016/j.ajog.2017.11.593>
     Locator: Abstract, sentence 13, fragment 2 of 2. Retrieved 2026-10-14T18:18:27Z. Source state: Current. Snapshot hash: fd5963be0dc6a68d10e4c9182534ffbe44918aff9de7eb9f4500341a687c9078.
     How it applies: PubMed abstract.
  10. Supports: Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study (Publication, edition PubMed record (abstract and bibliographic data) from NCBI E-utilities, retrieved 2026-10-14. The full text and the version of record were not read.) <https://doi.org/10.1016/j.ajog.2017.11.593>
     Locator: Abstract, sentence 15, fragment 1 of 2. Retrieved 2026-10-14T18:18:27Z. Source state: Current. Snapshot hash: fd5963be0dc6a68d10e4c9182534ffbe44918aff9de7eb9f4500341a687c9078.
     How it applies: PubMed abstract.
  11. Supports: Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study (Publication, edition PubMed record (abstract and bibliographic data) from NCBI E-utilities, retrieved 2026-10-14. The full text and the version of record were not read.) <https://doi.org/10.1016/j.ajog.2017.11.593>
     Locator: Abstract, sentence 15, fragment 2 of 2. Retrieved 2026-10-14T18:18:27Z. Source state: Current. Snapshot hash: fd5963be0dc6a68d10e4c9182534ffbe44918aff9de7eb9f4500341a687c9078.
     How it applies: PubMed abstract.

## Connected pages

- Which fetuses are labelled small: Fetal growth restriction (fetus) (`maternal:fetal-growth-restriction`)
- Filed under this front: Imaging and monitoring (`maternal:front-imaging-and-monitoring`)

## Provenance

Content hash: ce1745f592ff70d072983e31c249b356813483e6c7e576fcde981bc12dd875be
Last substantive edit: 2026-10-14
Evidence last checked: 2026-10-14