Term Pregnancy Evaluation of Fetal Weight: The Essential Role of Obstetric Ultrasound

Obstetric ultrasound at term pregnancy, defined as the period between 37 and 42 weeks of gestation, plays a crucial role in assessing fetal well-being and guiding clinical decisions. As pregnancy reaches its final stage, an ultrasound provides real-time visualization of fetal activity and the intrauterine environment. These assessments contribute significantly to the prediction and management of potential perinatal complications [1, 2, 3].

The primary objectives of performing an ultrasound at term include the assessment of amniotic fluid volume, where conditions like oligohydramnios or polyhydramnios may indicate underlying pathologies or complications requiring intervention [4]. Placental assessment is crucial for determining its location, maturation status, and potential abnormalities such as placental insufficiency [1]. Furthermore, fetal positioning and presentation, including breech or transverse lie, can influence delivery planning and the need for external cephalic version or cesarean delivery [5]. Another key component of the term ultrasound is umbilical artery Doppler flow assessment, which evaluates the flow velocity waveforms in the fetal umbilical artery. Increased resistance in the umbilical artery Doppler flow is associated with higher risks of perinatal mortality [6]. The examination should also include the evaluation of fetal growth and estimated fetal weight (EFW), identifying small for gestational age (SGA) or macrosomic fetuses, which are associated with various obstetric risks [7]. To date, no international guidelines recommend the routine use of ultrasound at term for assessing fetal weight, for the accuracy of EFW is compromised by large intra and interobserver variability. Errors in the range of 10%–15% are common, and tend to be even greater in fetuses of greatest clinical concern, such as those who are small or large for gestational age. These limitations help explain why routine term ultrasound for fetal weight estimation is not currently recommended. Nevertheless, accumulating evidence suggests that fetal weight estimation in the late third trimester may be valuable for identifying and stratifying obstetric risks for labor and delivery [8].

Data obtained from term ultrasounds have a significant impact on clinical decision-making, particularly in the context of labor induction in cases of suspected growth restriction or oligohydramnios [9]. The mode of delivery planning is influenced by findings such as macrosomia or malpresentation [10], and enhanced monitoring is recommended when abnormalities are detected, prompting closer surveillance and possibly earlier intervention [11].

In conclusion, obstetric ultrasound at term represents a cornerstone in the assessment of fetal weight, offering real-time insights that guide obstetric management and decision-making, making it an invaluable tool for optimizing perinatal outcomes. Integrating this practice into routine term assessment not only enhances fetal monitoring and labor management, but also supports evidence-based clinical decisions aimed at reducing perinatal risks.

References

[1] Salomon LJ, Alfirevic Z, Da Silva Costa F, Deter RL, Figueras F, Ghi T, et al. ISUOG Practice Guidelines: ultrasound assessment of fetal biometry and growth. Ultrasound in Obstetrics & Gynecology: the Official Journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2019; 53: 715–723. https://doi.org/10.1002/uog.20272.

[2] Granese R, Gulino FA, Incognito GG, Cianci S, Martinelli C, Ercoli A. Ultrasonographic Prenatal Diagnosis: Unveiling the Path to Improved Antenatal Care. Journal of Clinical Medicine. 2023; 12: 4450. https://doi.org/10.3390/jcm12134450.

[3] American College of Obstetricians and Gynecologists. ACOG Practice Bulletin No. 204: fetal growth restriction. Obstetrics and Gynecology. 2019; 133: e97–e109. https://doi.org/10.1097/AOG.0000000000003070.

[4] Magann EF, Chauhan SP, Doherty DA, Magann MI, Morrison JC. The evidence for abandoning the amniotic fluid index in favor of the single deepest pocket. American Journal of Perinatology. 2007; 24: 549–555. https://doi.org/10.1055/s-2007-986689.

[5] Hofmeyr GJ, Kulier R, West HM. External cephalic version for breech presentation at term. The Cochrane Database of Systematic Reviews. 2015; 2015: CD000083. https://doi.org/10.1002/14651858.CD000083.pub3.

[6] Karsdorp VH, van Vugt JM, van Geijn HP, Kostense PJ, Arduini D, Montenegro N, et al. Clinical significance of absent or reversed end diastolic velocity waveforms in umbilical artery. Lancet (London, England). 1994; 344: 1664–1668. https://doi.org/10.1016/s0140-6736(94)90457-x.

[7] Hadlock FP, Deter RL, Harrist RB, Park SK. Estimating fetal age: computer-assisted analysis of multiple fetal growth parameters. Radiology. 1984; 152: 497–501. https://doi.org/10.1148/radiology.152.2.6739822.

[8] Vayssiere C. Prospective individual participant data meta-analysis of pessary trials for preterm birth prevention (PROMPT) in twins. In 2024 SMFM Global Congress. Rome, Italy. Wiley. 2024. https://doi.org/10.1002/pmf2.12045.

[9] Boers KE, Vijgen SMC, Bijlenga D, van der Post JAM, Bekedam DJ, Kwee A, et al. Induction versus expectant monitoring for intrauterine growth restriction at term: randomised equivalence trial (DIGITAT). BMJ (Clinical Research Ed.). 2010; 341: c7087. https://doi.org/10.1136/bmj.c7087.

[10] Chauhan SP, Grobman WA, Gherman RA, Chauhan VB, Chang G, Magann EF, et al. Suspicion and treatment of the macrosomic fetus: a review. American Journal of Obstetrics and Gynecology. 2005; 193: 332–346. https://doi.org/10.1016/j.ajog.2004.12.020.

[11] Caradeux J, Martinez-Portilla RJ, Peguero A, Sotiriadis A, Figueras F. Diagnostic performance of third-trimester ultrasound for the prediction of late-onset fetal growth restriction: a systematic review and meta-analysis. American Journal of Obstetrics and Gynecology. 2019; 220: 449–459.e19. https://doi.org/10.1016/j.ajog.2018.09.043.