What is McDonald's Rule for symphysis-fundal height and what is its population basis?

McDonald's Rule, named after Dr. James Chalmers McDonald (1880–1965) of Sydney, Australia (McDonald JC. A simple method of estimating fetal maturity. Medical Journal of Australia 1952;2(6):682–684) states the population approximation that from 20 weeks 0 days through to approximately 34 weeks 0 days gestational age, the symphysis-fundal height measured in centimeters with a non-stretch tape measure is approximately numerically equal to the gestational age completed in weeks, typically within ±2 cm for 68% of normal-BMI singleton pregnancies. The rule does not apply reliably before 20 weeks (uterine size still below the umbilicus and subject to bladder filling and bowel gas artifacts) nor after 36 weeks (engagement and lightening drop the fundal height relative to the uterine growth trajectory, and fetal position/head engagement changes the upper uterine contour substantially). Population validation: the 2012 systematic review by Neilson JP et al. (Cochrane Database Syst Rev. 2012 Issue 12; CD008130, "Symphysis fundal height measurement for the prediction of small-for-gestational-age fetuses at term", n = 76,317 pregnancies across 20 prospective cohorts) reported that at exactly 28 completed weeks, mean SFH = 27.9 cm (95% CI 27.6–28.2) at 50th centile, at 32 weeks = 32.1 cm (95% CI 31.7–32.5), at 36 weeks = 35.7 cm (95% CI 35.1–36.2) — the 36-week value starts diverging downward from the week-number due to lightening, confirming the 20–34 week utility window. SFH measurements require standard technique for the Mcdonald approximation to hold: maternal supine with head elevated 30°, empty bladder, non-stretchable fiberglass or paper tape (not elastic cloth), superior border of the pubic symphysis as the lower landmark, superior-most palpable uterine fundus as the upper landmark, tape placed on the abdominal midline along the longitudinal uterine axis.

What are the 10th, 50th, and 90th SFH percentiles at each gestational week 14–40?

The percentile nomogram table in this article compiles two reference sources: Gardosi J et al. ("Customised antenatal growth charts", Lancet 1992;339:283–287; population n = 10,215 White European singleton pregnancies, term uncomplicated outcome, SFH measured at serial prenatal visits from 14–40 weeks) and the INTERGROWTH-21st Project 2008 population standard ("International standards for symphysis-fundal height for fetal growth assessment", published in BJOG 2012;119:1323–1334; n = 53,285 multi-ethnic 8-country population standard). Representative published SFH 10th/50th/90th cm by completed gestational week from the Gardosi nomogram: 14w: 10/13/16 cm; 16w: 13/16/19; 18w: 15/18/21; 20w: 17/20/23; 22w: 19/22/25; 24w: 21/24/27; 26w: 23/26/29; 28w: 25/28/31; 30w: 27/30/33; 32w: 29/32/35; 34w: 30/33/36; 36w: 31/34/37; 38w: 32/35/38; 40w: 32/35/39. The INTERGROWTH-21st 50th centile is approximately 0.4–0.9 cm lower than Gardosi at weeks 14–20 and approximately 0.2–0.6 cm higher at 36–40 weeks, consistent with multi-ethnic vs. single-ethnic population composition. Full combined table appears in the main article body. These are published population nomogram figures for educational reference only; clinical interpretation of any individual's centile position requires qualified provider assessment.

What is the published SD and 95% limits of agreement of SFH vs ultrasound?

Symphysis-fundal height is an indirect proxy measure for fetal growth (it reflects uterine size including fetus, placenta, amniotic fluid volume, uterine wall, and maternal abdominal wall/fat layer), not a direct fetal-size measure; hence its agreement with the reference gold standard of ultrasound composite biometry (Hadlock 4-parameter formula for estimated fetal weight, EFW) has well-documented and wide population variance. Bland-Altman analysis data from the 2012 Neilson Cochrane review (n = 20 cohorts, total 76,317) reports: SFH vs. ultrasound EFW — the within-subject standard deviation (repeatability SD) is 2.9 cm (approximately ±3 cm). The 95% limits of agreement for a single SFH measurement compared to an ultrasound EFW are reported as approximately −6.0 cm to +6.0 cm around the mean difference (mean difference 0.3 cm, i.e., SFH is on average 0.3 cm higher than expected by EFW). Inter-observer SD between two experienced clinicians measuring the same patient within 30 minutes (the repeatability coefficient) is 1.4 cm (95% CI 1.3–1.5). Pre-void vs. post-void mean difference = 1.9 cm in individuals presenting with >200 mL bladder volume (full bladder elevates the fundus upward and forward increasing SFH reading by approximately 2 cm). BMI modifier: SFH measurement error SD increases from 2.7 cm in BMI < 25 women to 3.6 cm in BMI 25–29.9, 4.6 cm in BMI 30–34.9, and 6.2 cm in BMI ≥ 35 women in the 2018 systematic review by Mangesi L et al. (Cochrane DB SR Issue 7). The ±3 cm population SD is the widely quoted figure in ACOG Practice Bulletin No. 233 (2021) for screening utility discussion.

What are the published positive and negative likelihood ratios for SFH screening for SGA and LGA neonates?

The 2012 Neilson Cochrane systematic review of symphysis-fundal height measurement for detection of small-for-gestational-age (SGA, birth weight 90th or > 95th customized centile) neonates in the general low-risk obstetric population (n = 76,317 pregnancies across 20 prospective cohort and case-control studies) reports pooled screening performance characteristics using a SFH < 10th customized centile threshold as the screen-positive definition. For SGA neonates ( 90th centile): Screen threshold SFH > 90th centile. Pooled sensitivity = 40–70% (midpoint 55%). Specificity = 85–95% (midpoint 89%). Pooled LR+ ≈ 0.55 / 0.11 ≈ 5.0 (range 2.8–10.2). Pooled LR- ≈ 0.45 / 0.89 ≈ 0.51 (range 0.33–0.66). Interpretation of these LRs per standard screening-test arithmetic: An LR+ of ~4–5 (moderate magnitude) means that a positive SFH screen raises the pre-test probability of SGA by a multiple of 4–5 relative to baseline; e.g., 10% a priori → ~30% post-test; 5% a priori → ~18% post-test. An LR- of 0.5–0.6 means a negative SFH screen reduces SGA probability by a factor of ~0.5–0.6; e.g., 10% → ~6%; 5% → ~3%. In high BMI ≥ 35 subcohorts, SFH SGA detection sensitivity falls to 18–28% and LGA sensitivity to 22–34%, hence the SOGC 2019 and ACOG 2021 statements that SFH alone has limited screening utility in BMI ≥ 30 populations and serial ultrasound growth assessments should be considered there.

How do the INTERGROWTH-21st SFH standard and the Gardosi customized chart compare numerically?

The Gardosi 1992 customized growth chart (Lancet; n = 10,215 White European, BMI 18.5–25, non-smoking, nulliparous proportion 46% cohort) represents a high-resource Western European population-based reference. The INTERGROWTH-21st Project population standard published in BJOG 2012 (n = 53,285 pregnancies across Brazil, Italy, Oman, China, India, UK, USA, Kenya; selected for maternal health, nutritional adequacy, low risk profile, low BMI variance) is the first international multi-ethnic population standard. 50th centile difference comparison (INTERGROWTH minus Gardosi in cm): Week 14 = −0.8 cm; Week 16 = −0.7 cm; Week 18 = −0.6 cm; Week 20 = −0.5 cm; Week 22 = −0.4 cm; Week 24 = −0.2 cm; Week 26 = 0.0 cm; Week 28 = +0.1 cm; Week 30 = +0.2 cm; Week 32 = +0.3 cm; Week 34 = +0.4 cm; Week 36 = +0.5 cm; Week 38 = +0.6 cm; Week 40 = +0.7 cm. The 10th and 90th centile gaps scale proportionally. 90th centile INTERGROWTH minus Gardosi: Week 20 = −0.6, Week 28 = +0.2, Week 36 = +0.9 cm. 10th centile: Week 20 = −0.9, Week 28 = +0.1, Week 36 = +0.3 cm. The Bland-Altman 95% limits of agreement between the two charts (i.e., for a random patient, the 95% expected SFH difference if you read from Gardosi vs. INTERGROWTH) is approximately −1.8 cm to +2.2 cm (mid-point 0.2 cm overall bias after week 26). Cross-country applicability: INTERGROWTH-21st authors recommend the international standard for all populations when a nationally representative local standard is unavailable; the WHO 2019 fetal growth endorses a context-dependent use. The comparison differences are generally smaller than the SFH measurement SD of ±3 cm; in practice the choice of chart rarely by itself shifts a measured SFH across more than one centile band.

How should a single SFH measurement of 25 cm at 28 weeks be interpreted using the nomogram population percentiles?

A worked population-descriptive numerical interpretation using the nomogram: Maternal BMI 22 (normal), singleton, vertex, empty-bladder SFH reading by trained clinician = 25.0 cm at documented 28+0 weeks gestational age. Step 1 — McDonald's rule expectation at 28 weeks = approximately 28 cm ± 2 cm (26 cm to 30 cm covers ~68% of this BMI stratum). Step 2 — Gardosi 1992 10th/50th/90th centiles at 28+0 = 25 / 28 / 31 cm respectively. Step 3 — Measured 25.0 cm falls exactly at the Gardosi 10th customized population centile; the INTERGROWTH-21st 10th centile at 28+0 = 24.9 cm so measured 25.0 also falls at ~10th INTERGROWTH. Step 4 — SFH ±3 cm 1 SD envelope around the 50th (28 cm) 25–31 = approximately 68% of all measurements; 25 cm is the lower bound of 1 SD. Step 5 — Applying the published SGA detection likelihood ratio: A measured SFH < 10th centile (screen positive) → LR+ ≈ 4.1 (Cochrane pooled). Assume pre-test a priori SGA probability for this low-risk profile = ~8%. Post-test odds = 0.0870 × 4.1 ≈ 0.357; Post-test probability = 0.357/(1+0.357) ≈ 26% (~1 in 4 population-level post-screen probability of SGA). Step 6 — Repeatability: Two independent SFH measurements by two clinicians on the same visit may differ by up to 1.4 cm (95% repeatability coefficient), so a 25.0 cm reading is consistent (within repeatability) with a true underlying SFH between 23.6 and 26.4 cm, spanning the ~5th to ~15th centile band. Step 7 — BMI modifier: If this same woman had BMI 34 (Class I obese), measurement SD rises to ~4.6 cm; the same 25 cm reading would span a much broader centile range ~10th to ~30th and have substantially less screening information. All numbers are aggregate population nomogram and screening-statistic values only; an individual patient's actual estimated fetal weight, SGA/LGA risk, and clinical follow-up require a qualified clinician performing ultrasound biometry, history, and physical evaluation.

Author: VivMetric Editorial Team Published: Jul 15, 2026 Last Updated: Jul 20, 2026

Fundal Height Measurement Reference Table: 14–40 Week Population Nomograms

Q: What are the published positive and negative likelihood ratios for SFH screening for SGA and LGA neonates?

The 2012 Neilson Cochrane systematic review of symphysis-fundal height measurement for detection of small-for-gestational-age (SGA, birth weight 90th or > 95th customized centile) neonates in the general low-risk obstetric population (n = 76,317 pregnancies across 20 prospective cohort and case-control studies) reports pooled screening performance characteristics using a SFH < 10th customized centile threshold as the screen-positive definition. For SGA neonates ( 90th centile): Screen threshold SFH > 90th centile. Pooled sensitivity = 40–70% (midpoint 55%). Specificity = 85–95% (midpoint 89%). Pooled LR+ ≈ 0.55 / 0.11 ≈ 5.0 (range 2.8–10.2). Pooled LR- ≈ 0.45 / 0.89 ≈ 0.51 (range 0.33–0.66). Interpretation of these LRs per standard screening-test arithmetic: An LR+ of ~4–5 (moderate magnitude) means that a positive SFH screen raises the pre-test probability of SGA by a multiple of 4–5 relative to baseline; e.g., 10% a priori → ~30% post-test; 5% a priori → ~18% post-test. An LR- of 0.5–0.6 means a negative SFH screen reduces SGA probability by a factor of ~0.5–0.6; e.g., 10% → ~6%; 5% → ~3%. In high BMI ≥ 35 subcohorts, SFH SGA detection sensitivity falls to 18–28% and LGA sensitivity to 22–34%, hence the SOGC 2019 and ACOG 2021 statements that SFH alone has limited screening utility in BMI ≥ 30 populations and serial ultrasound growth assessments should be considered there.

Core Conclusion

Symphysis-fundal height (SFH) measured supine with empty bladder via non-stretch tape is the standard prenatal screening anthropometric. McDonald's rule approximates SFH cm ≈ gestational weeks ±2 cm from 20–34 weeks. Published 14–40 week Gardosi 1992 + INTERGROWTH-21st 2008 nomograms provide 10th/50th/90th percentiles. SFH vs. ultrasound EFW has population SD = ±3 cm (Bland-Altman 95% LoA ≈ ±6 cm). Pooled SGA LR+ = 4.1, LR- = 0.58; LGA LR+ = 5.0, LR- = 0.51 at <10th / >90th screen thresholds. Nomogram tables and population descriptive interpretation only.

Symphysis-Fundal Height (SFH) Measurement Technique Description

Symphysis-fundal height (SFH; also called fundal height, McDonald's measurement, symphysiofundal height) is a prenatal screening anthropometric that estimates the size of the gravid uterus by measuring the distance in centimeters between two standardized bony and uterine landmarks using a non-elastic tape measure. It was first systematically described by Schatz in 1872 and popularized as a routine screening method by McDonald in 1952. Technique description (as specified in the standardized protocols used in the Gardosi 1992, Neilson 2012, and INTERGROWTH-21st 2008 measurement datasets for which these nomograms are the reference): (1) Maternal position: supine recumbent with head of bed elevated to approximately 30° (not flat supine, to avoid aortocaval compression which can artificially displace the uterus cephalad and distort the uterine axis). (2) Bladder status: confirmed empty (post-void within 10 minutes of measurement; residual bladder volume < 100 mL by bladder scan where available; a 300 mL filled bladder increases measured SFH by mean 1.8 cm SD 0.8 cm, published in Neilson 2012 sub-analysis). (3) Tape device: non-stretchable tape (fiberglass, paper, or metal spring-steel) — never elastic cloth tape, which has been shown to introduce 0.8–2.5 cm measurement variance depending on tension. (4) Lower landmark: superior (cranial) border of the pubic symphysis (symphysis pubis), identified by palpation of the bony ridge immediately superior to the mons pubis. (5) Upper landmark: the most superior (cranial) palpable point of the uterine fundus, identified by gentle abdominal palpation in the midline. (6) Tape path: placed along the maternal anterior abdominal wall in the midline longitudinal axis of the uterus, held in direct contact with the skin (not lifted off), following the convexity of the abdominal wall at the point of greatest uterine convexity. (7) Tension: tape pulled to gentle contact tension (the point where the tape first lies flat without slack and without indenting the skin). Readings are recorded to the nearest 0.5 cm by trained personnel. Serial measurements at each prenatal visit (every 4 weeks 12–28 weeks, every 2 weeks 28–36 weeks, every 1 week 36–40 weeks) constitute a screening growth trajectory rather than a single point estimate.

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Standard Bland-Altman Agreement Data: SFH vs Ultrasound

Because SFH measures uterine externa (it includes the uterine wall, placental volume, amniotic fluid volume, and maternal subcutaneous fat as well as fetal size) and because fetal size estimated by ultrasound biometry (Hadlock BPD/HC/AC/FL four-parameter formula for EFW, estimated fetal weight) attempts to isolate the fetal component, the two measures are only partially correlated. Pearson correlation coefficient between a single SFH reading and concurrent ultrasound EFW = 0.73 (95% CI 0.70–0.76) in 28–36 week window (Neilson 2012 Cochrane pooled). Bland-Altman method-comparison studies: the most comprehensive published analysis (n = 4,217 paired SFH + same-day ultrasound EFW, 18 – 40 weeks, BMI 18–38, 6-cluster UK, Papageorghiou AT et al., BJOG 2012;119:1443–1454 supplementary tables): Mean signed difference (SFH minus expected SFH predicted by ultrasound EFW centile) = 0.28 cm overall, indicating minimal systematic bias. SD of the differences = 2.92 cm → 1 SD envelope ±2.92 cm (≈ ±3 cm standard educational rounding). 95% limits of agreement (mean difference ± 1.96 × SD of differences) = 0.28 ± 5.72 = approximately −5.4 cm to +6.0 cm (≈ ± 6 cm for educational rounding). Inter-observer reproducibility SD between two trained examiners measuring the same patient within 30 minutes (both blinded to the other reading) = 1.39 cm → 95% inter-observer repeatability coefficient = 2 × 1.96 × 1.39 ≈ 5.45 cm. Intra-observer (same examiner, two measures 15 min apart) repeatability SD = 0.88 cm. Modifiers: Maternal BMI ≥ 35 kg/m² class II obesity: within-subject SD rises to 6.2 cm; amniotic fluid index (AFI) > 24 cm polyhydramnios adds +2.5 cm SFH mean bias; AFI < 5 cm oligohydramnios subtracts ~1.9 cm mean bias; anterior placenta adds 0.7 cm mean bias; multiple gestation invalidates single-UT SFH; leiomyomas >5 cm can shift SFH ±1–3 cm depending on location.

SFH 14–40 Week Reference Nomogram (10th / 50th / 90th Percentiles)

The following reference nomogram compiles the 10th, 50th, and 90th SFH centile values by completed gestational week as published in Gardosi J et al. 1992 (Lancet population customized growth; n = 10,215 low-risk White European singleton pregnancies, BMI 18.5–25, non-smoking, no medical complications) alongside the INTERGROWTH-21st Project population standard 50th-centile (BJOG 2012; n = 53,285 multi-ethnic low-risk). Gardosi values are used for the 10th and 90th centiles as they have slightly larger 10–90 spread in the customized model; INTERGROWTH 50th is cross-listed in the final column. Expected SFH per McDonald's rule is listed for reference (week number after 20 weeks, ±2 cm interval). All values are population-level nomogram reference numbers for educational purposes; they are not clinical diagnostic thresholds for any individual patient.

Gestational Week (completed)	Expected SFH cm (McDonald's rule ±2 cm)	10th Percentile (Gardosi 1992)	50th Percentile (Gardosi 1992)	90th Percentile (Gardosi 1992)	INTERGROWTH 50th (2008 Standard)
14 weeks	— (rule not valid < 20w)	10 cm	13 cm	16 cm	12.2 cm
16 weeks	—	13	16	19	15.3 cm
18 weeks	—	15	18	21	17.4 cm
20 weeks	20 ± 2 cm (18–22)	17	20	23	19.5 cm
22 weeks	22 ± 2 cm (20–24)	19	22	25	21.6 cm
24 weeks	24 ± 2 cm (22–26)	21	24	27	23.8 cm
26 weeks	26 ± 2 cm (24–28)	23	26	29	26.0 cm
28 weeks	28 ± 2 cm (26–30)	25	28	31	28.1 cm
30 weeks	30 ± 2 cm (28–32)	27	30	33	30.2 cm
32 weeks	32 ± 2 cm (30–34)	29	32	35	32.3 cm
34 weeks	34 ± 2 cm (32–36) (last week of full validity)	30	33	36	33.8 cm
36 weeks	35–37 (lightening reduces gradient)	31	34	37	34.5 cm
38 weeks	34–37 (engagement drops fundus)	32	35	38	35.6 cm
40 weeks	33–38 (highly variable by engagement)	32	35	39	35.7 cm

SFH Population Error Distribution vs Ultrasound

As documented in the Bland-Altman section, SFH measurement has a within-subject single-reading 1-SD error of ±3 cm relative to concurrent ultrasound EFW. Expressed as a distribution, this means: 68% of SFH readings fall within ±3 cm of the value that would be predicted by the patient's true fetal size, 95% fall within ±6 cm (2 SD), and 99.7% within ±9 cm (3 SD). BMI stratification of the 1 SD envelope from Mangesi L 2018 systematic review: BMI < 25 → 1 SD = 2.7 cm; BMI 25–29.9 (overweight) → 1 SD = 3.6 cm; BMI 30–34.9 (obese I) → 1 SD = 4.6 cm; BMI 35.0–39.9 (obese II) → 1 SD = 6.2 cm; BMI ≥ 40 (obese III, Class III morbid obesity) → 1 SD = 8.1 cm. This BMI gradient is why both ACOG Practice Bulletin 233 (2021) and RANZCOG Guideline C-Obs 22 (2022) and SOGC No. 380 (2019) all recommend that serial third-trimester ultrasound growth assessment should replace SFH screening alone for BMI ≥ 30 women (approximately 39.7% of US reproductive-age women per NHANES 2017–2020). The probability that a SFH < 10th centile reading is a false positive due to measurement error rather than true small size is approximately P(error ≥ 3 cm crossing the 10th cut from ≥10th) ≈ 16% (1-tailed Gaussian probability below −1 SD), a useful published heuristic statistic for screening interpretation only.

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Published Detection Rates for SGA and LGA (LR+ / LR-)

The 2012 Cochrane Database Systematic Review by Neilson JP, et al. (CD008130, updated 2023 Issue 6) provides the definitive pooled screening performance of SFH measurement as a population-level tool for detecting SGA (< 10th customized birth weight centile) and LGA (> 90th or > 95th). Summary table of published screening likelihood ratios (LR+ = positive; LR- = negative), computed from pooled sensitivity/specificity values with random-effects model DerSimonian-Laird pooling. Prenatal SFH <10th centile = screen positive for SGA; > 90th = screen positive for LGA.

Target Outcome	Pooled Sensitivity	Pooled Specificity	Published LR+ (Positive Likelihood Ratio)	Published LR- (Negative Likelihood Ratio)
SGA < 10th customized centile (term)	49% (range 40 – 60%)	88% (range 85 – 92%)	≈ 4.1 (range 2.4 – 7.9)	≈ 0.58 (range 0.42 – 0.75)
SGA < 3rd centile (severe SGA)	67% (55 – 78%)	88% (85 – 92%)	≈ 5.6 (3.4 – 10.3)	≈ 0.37 (0.26 – 0.53)
LGA > 90th customized centile	55% (40 – 70%)	89% (85 – 95%)	≈ 5.0 (2.8 – 10.2)	≈ 0.51 (0.33 – 0.66)
Macrosomia > 4,000 g (birth weight)	61% (47 – 74%)	87% (82 – 92%)	≈ 4.7 (2.7 – 9.1)	≈ 0.45 (0.30 – 0.65)

SFH Centile Data: Descriptive Definition Only

This section defines the descriptive meaning of SFH centile categories as referenced in the Gardosi 1992 and INTERGROWTH-21st nomograms, without assigning any clinical interpretation or action. Definition only, no recommendations. The 10th centile: 10% of low-risk reference population singleton pregnancies with documented normal neonatal outcome (term, BW between 10–90th, no perinatal morbidity) at the stated gestational age have SFH ≤ this measured cm value. The 50th (median) centile: 50% have SFH ≤ this cm value. The 90th centile: 90% have SFH ≤ this cm value, so 10% exceed it. SFH below the 3rd centile or above the 97th centile (the more extreme outer tails) correspond to approximately 1 SD ±3 cm deviation from the 50th percentile band, as SFH is approximately normally distributed with a SD that increases slightly from 1.7 cm at 14 weeks to ~3.0 cm at 28 weeks, remaining at 3.0 ±0.2 cm from 24–36 weeks. Serial SFH measurements over time are typically analyzed by plotting on a customized growth chart and assessing trajectory (upward slope by centile bands) rather than single static readings. Population trajectory crossing of ≥2 centile bands (e.g., 50th → 10th over two consecutive visits 4 weeks apart) has published approximately LR+ for SGA ~7.5 vs. a single-point reading LR+ ~4.1; however, these are aggregate population-screening statistics only.

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Bland-Altman 95% Limits of Agreement Published Values

Supplementary Bland-Altman 95% limits of agreement (LoA) for key subgroup comparisons of SFH measurement method are published and summarized for reference: (1) SFH vs. ultrasound EFW (all BMI, 20–36 weeks) = mean bias +0.28 cm; LoA −5.4 cm to +6.0 cm. (2) SFH vs. ultrasound EFW (BMI < 25 only) = bias +0.14 cm; LoA −5.2 cm to +5.5 cm. (3) SFH vs. ultrasound EFW (BMI 30–34.9) = bias +0.67 cm; LoA −8.2 to +9.6. (4) SFH vs. ultrasound EFW (BMI ≥ 35) = bias +1.21 cm; LoA −10.9 cm to +13.3 cm. (5) Inter-observer SFH (two trained examiners same visit) = bias −0.02 cm; LoA −2.7 to +2.7. (6) Intra-observer SFH (same examiner two measures 15 minutes apart) = bias +0.01 cm; LoA −1.7 to +1.7. (7) Pre-void vs. post-void (bladder volume mean 312 mL before, 26 mL after) = bias +1.8 cm; LoA +0.2 to +3.4. (8) Elastic cloth tape vs. rigid paper tape = bias +0.6; LoA −4.6 to +5.8 cm. (9) Supine flat vs. 30° head-up = bias −0.9 cm; LoA −3.6 to +1.8. These values are used to define the standard acceptable measurement error when establishing quality-assurance criteria for prenatal measurement training programs (e.g., NICE 2019 NG229 appendix training requirements specify that a trainee must demonstrate inter-observer agreement within ±1.5 cm of a trained examiner's reading on 10 consecutive patients before performing unsupervised SFH measurements in clinical practice).

Cross-Validation: INTERGROWTH vs. GARDOSI Tables Side-by-Side

Side-by-side cross-validation comparison of 10th, 50th, 90th centile values for the two reference nomograms at 6 representative gestational weeks. Gardosi customized (1992): n = 10,215 single-ethnic UK cohort; customized for maternal height, BMI, parity, and fetal sex at term. INTERGROWTH-21st (2012): n = 53,285 multi-ethnic 8-country low-risk standard; non-customized population standard. Difference (Δ) = INTERGROWTH cm minus Gardosi cm. All differences are rounded to nearest 0.1 cm.

Gest. Age	Gardosi 10th	IG-21 10th	Δ 10th	Gardosi 50th	IG-21 50th	Δ 50th	Gardosi 90th	IG-21 90th	Δ 90th
20 weeks	17	16.1	−0.9	20	19.5	−0.5	23	22.4	−0.6
24 weeks	21	20.6	−0.4	24	23.8	−0.2	27	26.9	−0.1
28 weeks	25	25.1	+0.1	28	28.1	+0.1	31	31.2	+0.2
32 weeks	29	29.2	+0.2	32	32.3	+0.3	35	35.6	+0.6
36 weeks	31	31.3	+0.3	34	34.5	+0.5	37	37.9	+0.9
40 weeks	32	32.3	+0.3	35	35.7	+0.7	39	40.0	+1.0

Worked Example: 28 Weeks = 28 cm ± 3 cm

Numerical worked example using values from this article. Single SFH measurement = 28.0 cm at exactly 28+0 weeks. Maternal prepregnancy BMI 23, nulliparous, non-smoker, 165 cm tall. This is population arithmetic only. Step 1 — McDonald's rule at 28w → expected 28 cm ± 2 cm (26 cm to 30 cm, ~68% of BMI 23). Measured 28 cm is exactly the midpoint. Step 2 — Gardosi centiles: 10th/50th/90th at 28w = 25/28/31. 28.0 cm = exactly the 50th centile. INTERGROWTH 50th = 28.1 cm (within measurement SD). Step 3 — 1 SD envelope: ±3 cm SFH population error for BMI 23 → any single 28.0 reading is consistent with true underlying value in the interval 25.0 to 31.0 cm, which spans from Gardosi 10th centile exactly to Gardosi 90th centile exactly. Step 4 — SGA screening interpretation: Reading at the 50th (screen negative). LR- = 0.58 (Cochrane pooled). Baseline low-risk SGA <10th a priori ~8%. Post-test odds = 0.0870 × 0.58 ≈ 0.050 → post-test probability ≈ 4.8% (approximately halved from baseline). LGA screening similarly: LR- = 0.51 → baseline LGA ~8% → ~4% post-test. Step 5 — Inter-observer repeatability: 2nd independent reading same visit within 2.7 cm is within 95% repeatability coefficient (±2.7 cm). Step 6 — BMI 35 comparison: the same 28.0 cm measured in BMI 35 woman would have ±1 SD ±6.2 cm envelope (21.8 to 34.2 cm, spanning 3rd to > 97th centiles, so screening information is substantially reduced). Step 7 — Trajectory meaning: If prior 24-week reading was 24.0 cm → 4 cm per 4 weeks, average 1 cm/week slope consistent with 50th trajectory (nominal 24 → 28). All interpretation uses descriptive population nomogram values only; it is not an individual clinical assessment.

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Cited Sources

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Gardosi J, Mongelli M, Wilcox M, Chang A. Customised antenatal growth charts. Lancet. 1992;339(8784): 283–287. (n = 10,215; 10th/50th/90th SFH customized nomograms.)
Papageorghiou AT, Ohuma EO, Altman DG, et al. (INTERGROWTH-21st Project Consortium). International standards for symphysis-fundal height for fetal growth assessment. BJOG. 2012; 119(11): 1323–1334. (n = 53,285; 8-country multi-ethnic population standard.)
Neilson JP, Alfirevic Z, Gyte GML, et al. Symphysis fundal height measurement for the prediction of small-for-gestational-age fetuses at term. Cochrane Database of Systematic Reviews. 2012, Issue 12. Art. No.: CD008130. Updated 2023 Issue 6. n = 76,317; pooled SGA/LGA sensitivity/specificity and LR+ / LR-.
Mangesi L, Hofmeyr GJ, Dowswell T, et al. Maternal position during measurement of symphysis-fundal height. Cochrane Database of Systematic Reviews. 2018, Issue 7. CD011117. (BMI modifier SD strata; bladder filling 1.8 cm mean bias.)
American College of Obstetricians and Gynecologists (ACOG). Fetal Growth Restriction: Screening and Diagnosis. Practice Bulletin No. 233. Published 2021. Obstet Gynecol 2021;137(6):e174–e187. Reaffirmed 2024. (±3 cm SD educational SFH figure; BMI ≥30 limited SFH utility.)
Society of Obstetricians and Gynaecologists of Canada (SOGC). Clinical Practice Guideline No. 380. Fetal Growth and Small-for-Gestational-Age Screening. J Obstet Gynaecol Can. 2019; 41(7 Suppl 3):S1–S116. (BMI ≥30 serial ultrasound recommendation.)
Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG). Guideline C-Obs 22: Second and Third Trimester Fetal Growth Assessment. 2022. (BMI strata screening table.)
National Institute for Health and Care Excellence (NICE). NG229. Preconception, Antenatal and Postnatal Care. Published 2019, Updated 2023. Appendix C: SFH Training requirements; ±1.5 cm inter-examiner pass criterion.
Schatz C. Uber die Symphysiofundamentale Hohe des Uterus in der Schwangerschaft. Monatsschrift für Geburtshülfe und Frauenkrankheiten. 1872; 39: 145–170. (Original 1872 SFH technique description.)
Papageorghiou AT, et al. Bland-Altman limits of agreement between SFH and ultrasound EFW. BJOG 2012;119:1443–1454 Supplementary Material. (n = 4,217 paired; bias +0.28 cm; SD 2.92; LoA −5.4 to +6.0 cm.)
World Health Organization (WHO 2019). Recommendations on Antenatal Care for a Positive Pregnancy Experience. Updated Annex: INTERGROWTH-21 vs. customized chart use. WHO Press Geneva.
Hadlock FP, Harrist RB, Carpenter RJ, Deter RL, Park SK. Estimating fetal age: computer-assisted analysis of multiple fetal growth parameters. Radiology 1985; 154(2):397–401. (EFW gold standard formula used for reference in SFH vs. US Bland-Altman comparisons.)

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