Forward Weight Prediction among Small for Gestational Age, Average for Gestational Age, and Large for Gestational Age Neonates

Abstract

Objective

This study was aimed to evaluate the accuracy of the gestation-adjusted projection (GAP) forward projection model among neonates classified as small (SGA), appropriate (AGA), or large for gestational age (LGA), and to assess the impact of elevated maternal body mass index (BMI) on prediction accuracy. The GAP model uses percentile-based extrapolation to predict birth weight from remote ultrasounds, maintaining fetal weight percentile from scan to delivery, unlike traditional methods relying on static weight estimates near delivery.

Study Design

We conducted a retrospective review (2016–2023) of singleton, liveborn, nonanomalous pregnancies delivered after 28 weeks. Exclusions included multiples, major anomalies, stillbirth, and missing third-trimester growth ultrasounds or mid-gestational anatomical surveys. Among 1,559 records reviewed, 554 (35.5%) met inclusion criteria, with exclusions primarily due to missing third-trimester growth ultrasounds and mid-gestational anatomical surveys. This represents approximately 5.6% of total deliveries during the study period, reflecting our specific inclusion requirement for third-trimester growth assessments beyond routine prenatal care. GAP prediction accuracy was defined as birth weight prediction within 10% of actual, consistent with prior literature. Percent error and absolute percent error were also evaluated.

Results

Median absolute percent error for the cohort was 8.56% (interquartile range: 3.9, 15.2). Accuracy within 10% of actual birth weight was achieved in 51.4% of normal weight, 64.1% of overweight, and 58.0% of obese patients (p = 0.031). SGA infants were more often underestimated (median error: −15.79%) than AGA (−5.05%) or LGA (1.18%) infants (p < 0.001). Accuracy within 10% was achieved in 64.8% of AGA, 29.9% of SGA, and 66.9% of LGA infants (p < 0.001).

Conclusion

The GAP model demonstrates better accuracy in pregnancies with elevated maternal BMI and similar accuracy for LGA and AGA infants. Findings support its potential value in high-risk groups, such as those with obesity or suspected LGA.

Key Points

• GAP model shows 8.6% median error in weight estimate.

• SGA often underestimated; LGA more accurate.

• GAP performs well in overweight and obese patients.

Keywords

fetal weight estimation - gestation-adjusted projection method - maternal obesity - ultrasound biometry - pregnancy outcomes - obstetric ultrasonography

Publication History

Received: 28 June 2025

Accepted: 24 August 2025

Accepted Manuscript online:
25 August 2025

Article published online:
05 September 2025

• References

• 1 Hadlock FP, Harrist RB, Martinez-Poyer J. In utero analysis of fetal growth: a sonographic weight standard. Radiology 1991; 181 (01) 129-133
• 2 Tas EE, Kir EA, Yilmaz G, Yavuz AF. Accuracy of sonographic fetal weight estimation in full-term singleton pregnant women. Pak J Med Sci 2019; 35 (01) 34-38
• 3 Williams RL, Creasy RK, Cunningham GC, Hawes WE, Norris FD, Tashiro M. Fetal growth and perinatal viability in California. Obstet Gynecol 1982; 59 (05) 624-632
• 4 Spinnato JA, Allen RD, Mendenhall HW. Birth weight prediction from remote ultrasound examination. Obstet Gynecol 1988; 71 (6 Pt 1): 893-898
• 5 Hendler I, Blackwell SC, Bujold E. et al. The impact of maternal obesity on midtrimester sonographic visualization of fetal cardiac and craniospinal structures. Int J Obes Relat Metab Disord 2004; 28 (12) 1607-1611
• 6 Thornburg LL, Barnes C, Glantz JC, Pressman EK. Sonographic birth-weight prediction in obese patients using the gestation-adjusted prediction method. Ultrasound Obstet Gynecol 2008; 32 (01) 66-70
• 7 Deter RL, Rossavik IK, Carpenter RJ. Development of individual growth standards for estimated fetal weight: II. Weight prediction during the third trimester and at birth. J Clin Ultrasound 1989; 17 (02) 83-88
• 8 Mongelli M, Gardosi J. Gestation-adjusted projection of estimated fetal weight. Acta Obstet Gynecol Scand 1996; 75 (01) 28-31
• 9 Pressman EK, Bienstock JL, Blakemore KJ, Martin SA, Callan NA. Prediction of birth weight by ultrasound in the third trimester. Obstet Gynecol 2000; 95 (04) 502-506
• 10 Bradley R, Sullivan C, Perry R, DiSilvestro A. Estimating Fetal Weight with Third Trimester Ultrasonography: How Do We Measure Up? [Oral Presentation]. Carilion Clinic Resident Research Day; 2021
• 11 Brenner WE, Edelman DA, Hendricks CH. A standard of fetal growth for the United States of America. Am J Obstet Gynecol 1976; 126 (05) 555-564
• 12 Hoopmann M, Kagan KO, Sauter A, Abele H, Wagner P. Comparison of errors of 35 weight estimation formulae in a standard collective. Geburtshilfe Frauenheilkd 2016; 76 (11) 1172-1179
• 13 Aye AA, Agida TE, Babalola AA, Isah AY, Adewole ND. Accuracy of ultrasound estimation of fetal weight at term: a comparison of Shepard and Hadlock methods. Ann Afr Med 2022; 21 (01) 49-53
• 14 Chauhan SP, Magann EF. Screening for fetal growth restriction. Clin Obstet Gynecol 2006; 49 (02) 284-294
• 15 Shittu AS, Kuti O, Orji EO. et al. Clinical versus sonographic estimation of foetal weight in southwest Nigeria. J Health Popul Nutr 2007; 25 (01) 14-23
• 16 Virginia Department of Health. Division of Policy and Evaluation, Behavioral Risk Factor Surveillance Survey 2012–2013: Weighted counts and weighted percents are weighted to population characteristics. Virginia Department of Health website; . Accessed December 15, 2024 at: https://www.vdh.virginia.gov/content/uploads/sites/68/2016/12/2012-2013PHYSHEALTH_Districts.pdf
• 17 Johnson JW, Longmate JA, Frentzen B. Excessive maternal weight and pregnancy outcome. Am J Obstet Gynecol 1992; 167 (02) 353-370 , discussion 370–372
• 18 Frentzen BH, Dimperio DL, Cruz AC. Maternal weight gain: effect on infant birth weight among overweight and average-weight low-income women. Am J Obstet Gynecol 1988; 159 (05) 1114-1117
• 19 Hong YH, Lee JE. Large for gestational age and obesity-related comorbidities. J Obes Metab Syndr 2021; 30 (02) 124-131