RCOG World Congress 2023

Objective

To determine accuracy of scan in predicting fetal birthweight after 37week gestation (GA) in women with BMI less than 35.

Design

A retrospective audit of women BMI<35, delivering within 2 weeks of growth scan after 37 weeks in singleton pregnancies in a single institution.

Methodology

•Women delivered > 37wks

•25 months’ time period.

•Growth scan within 2wks of delivery

•Exclusion: Delivery < 37weeks GA, multiple pregnancy, and maternal BMI>35

•Analysis of Maternal characteristics, Estimated fetal weight (EFW) on scan and birth weight (Bwt), interval between scan & delivery and operators.

•Percentage (%) difference in weight calculated as {(Bwt- EFW)/EFW} x100.

•Primary outcome: How many of our scans fell withing +/-10% and +/-15% of the Bwt within 2 weeks and 1 week of delivery

•Secondary outcomes include % Wt difference related to interval between scan & delivery, maternal BMI and the sonographer

Results

•451 out of 115 women fulfilled inclusion criteria

•Mean Maternal BMI: 25.1

•Range GA at delivery: 37-42wk

•Median Interval between scan & delivery: Day 8

•Mean weight error: 460.5 g. SD 236.9.

•213 women delivered within one week

•No major difference detected between scan interval, % weight difference, maternal BMI and the different sonographers

Conclusion

•Scans done >37wks can accurately predict upto 91% +/-15% of Bwt in women BMI <35

•This study adds to literature on reliability of obstetrics scans >37weeks GA; giving clinicians confidence when counselling women and making clinical decisions.

•Limitations include restriction of maternal BMI and the use of crude and percentage weight difference instead of centiles.

•We propose to look at the EFW centile & compare them with Bwt centiles, clinical decisions made on the extreme centiles and scan accuracy in women of different BMIs to widen our applicability.

RCOG World Congress 2023

Is scan accurate in estimating birth weight after 37 weeks?

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