How should a borderline uterine size be evaluated and managed in pregnant and non‑pregnant patients?

Evaluation and Management of Borderline Uterine Size

When uterine size is borderline or discrepant with expected gestational age, immediate ultrasound evaluation with fetal biometry and umbilical artery Doppler is indicated to rule out fetal growth restriction or macrosomia.

In Pregnant Patients

Initial Assessment Triggers

Ultrasound evaluation should be performed immediately when any of the following criteria are met:

• Fundal height >3 cm less than gestational age in weeks (McDonald's rule) 1, 2, 3
• Fundal height <10th percentile on customized growth charts 1, 2, 3
• Slow or static growth with <5 mm change in fundal height over 14 days 1, 3

Comprehensive Ultrasound Protocol

When borderline uterine size is identified, the ultrasound evaluation must include:

• Estimated fetal weight (EFW) and abdominal circumference (AC) to assess for macrosomia (>90th percentile) or growth restriction (<10th percentile) 3
• Umbilical artery Doppler to evaluate placental function and guide surveillance frequency 3
• Amniotic fluid volume assessment with normal maximum vertical pocket ≥2 cm 3
• Detailed anatomical examination if early growth restriction (<32 weeks) is suspected, as up to 20% may have fetal anomalies or chromosomal abnormalities 3

Surveillance Based on Findings

If macrosomia is suspected (EFW >90th percentile) with normal Doppler:

• Serial ultrasounds every 2 weeks to evaluate growth 3

If growth restriction is detected (EFW <10th percentile) with normal Doppler:

• Serial ultrasounds every 2 weeks 3
• Weekly umbilical artery Doppler 3

If abnormal Doppler is detected:

• Weekly Doppler surveillance 3
• Consider delivery at 37 weeks 3

Important Clinical Caveats

Fundal height measurements are unreliable and should be replaced with ultrasound in:

• Women with obesity 1, 2
• Women with fibroid uterus 1, 2
• Women with abdominal distention or increased body mass index 1

The sensitivity of fundal height drops significantly in obese patients, and clinicians should proceed directly to ultrasound in these cases rather than relying on clinical examination. 2

Special Pregnancy Considerations

• In gestational diabetes or history of macrosomia, serial ultrasounds should be performed to evaluate growth and detect potential complications 3
• Genetic testing, including chromosomal microarray analysis, should be offered in cases of unexplained growth restriction 3

In Non-Pregnant Patients

Normal Reference Values

Uterine volume varies significantly by age and parity:

• Nulliparous women: Mean dimensions 72.8 mm × 42.8 mm × 32.4 mm 4
• Multiparous women: Mean dimensions 90.8 mm × 51.7 mm × 43.0 mm 4
• Overall reproductive age: Mean dimensions 86.6 mm × 49.6 mm × 40.6 mm 4
• Normal volume range: 15-56 cm³ in women with normal uterus 5

Age-Related Changes

Uterine size increases across childhood, with faster increase during adolescence reflecting puberty, followed by slow progressive rise during adult life, with approximately 84% of variation in uterine volume up to age 40 due to age alone. 6

• Mean uterine length increases to 72 mm at age 40 years 7
• Mean length decreases to 42 mm at age 80 years 7
• Gravidity is associated with greater uterine length, width, and anteroposterior diameter 7

Clinical Significance

Ultrasonographic measurement of uterine size is valuable for predicting pathologies associated with abnormal uterine size, particularly in young and elderly women with menorrhagia. 5

• Uterine size is significantly associated with parity and age, but not with body mass index 4
• Assessment is helpful in disorders of sex development, precocious or delayed puberty, infertility, and menstrual disorders 6

When to Investigate Further

Borderline measurements in non-pregnant patients warrant investigation when:

• Measurements fall outside expected ranges for age and parity 6, 4, 7
• Clinical symptoms (menorrhagia, pelvic pain) accompany borderline findings 5
• Serial measurements show unexpected changes 7