CRL of 45 mm on 2024-06-01
- Input
- Exame: 1º/06/2024 · CCN: 45 mm
- Expected output
- IG: 11 semanas e 1 dia · DPP estimada: 19/12/2024
The EDD comes from adding (40 − 11.169) × 7 ≈ 202 rounded days to the exam date.
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when to correct due date by ultrasound LMP difference
When the exam date is entered, this calculator adds the gestational age it estimated from biometry to 40 weeks and returns a second estimated due date, calculated as the exam date plus (40 minus the estimated GA) times 7 days, rounded. This page explains that calculation and the criteria that guide when it should replace the LMP-based EDD.
The EDD comes from adding (40 − 11.169) × 7 ≈ 202 rounded days to the exam date.
A 5-day difference falls below the 7-day threshold cited for the 1st trimester, so the original EDD does not change.
10 days exceeds the 7-day threshold cited for the 1st trimester, which commonly justifies correcting by biometry.
CRL (Crown-Rump Length) in the 1st trimester (weeks 6–14) is the most precise parameter, with a margin of error of only ± 3–5 days. After week 14, composite biometry (BPD + HC + AC + FL) tends to be more accurate than any single measurement. Precision decreases progressively throughout gestation.
Because at that stage normal biological variation between fetuses is large enough that biometry alone cannot reliably distinguish a small baby from a wrong EDD. Prenatal care commonly keeps the EDD established in the 1st trimester, precisely because of that growing uncertainty.
No. It only computes the GA and the estimated EDD from the entered measurement and displays the number, it does not automatically compare that to a prior EDD or apply any discordance threshold. The decision to correct belongs to whoever interprets both results.
Yes. The calculator uses the composite gestational age (the weighted average of all entered measurements) to compute the EDD, so adding a second measurement can shift the result relative to what a single measurement alone would indicate, in the direction of whatever discordance exists between them.
Medical disclaimer: this calculation is educational and does not replace physician evaluation. Biometric measurements have inherent margin of error and must always be interpreted in clinical context.
Select the biometric measurement type from your ultrasound report, enter the value in millimeters, and optionally enter the exam date to get the estimated EDD.
Values entered remain only in your browser. We do not store or transmit this data.