CLINICAL TOOL
Pregnancy Dating & EDD Calculator
Calculate Estimated Date of Delivery (EDD) using Last Menstrual Period (LMP), Crown-Rump Length (CRL), or IVF transfer dates. Compliant with ACOG and ISUOG guidelines.
Clinical Purpose
To accurately establish the gestational age (GA) and Estimated Date of Delivery (EDD), which is foundational for timing obstetric interventions, interpreting screening tests, and assessing fetal growth.
Inputs
- Last Menstrual Period (LMP) Date
- Ultrasound Date and Crown-Rump Length (CRL) or Head Circumference (HC)
- IVF Embryo Transfer Date and Embryo Age (e.g., Day 3 or Day 5)
Formula & Guideline Source
ACOG Committee Opinion No. 700 (Methods for Estimating the Due Date), ISUOG Practice Guidelines (Ultrasound from 11 to 13+6 weeks).
Limitations
Ultrasound dating is most accurate in the first trimester (CRL up to 84mm). Beyond 14 weeks, dating is based on head circumference (HC) or biparietal diameter (BPD), which have wider error margins (±7-10 days).
FAQ
When should ultrasound dating replace LMP dating?
According to ACOG guidelines, if the ultrasound EDD differs from the LMP EDD by more than 5 days before 9 0/7 weeks of gestation, or more than 7 days between 9 0/7 and 13 6/7 weeks, the ultrasound EDD should be used.
How is IVF dating calculated?
For IVF pregnancies, the EDD is calculated by adding 266 days (38 weeks) to the date of oocyte retrieval. If the embryo transfer date is used, the embryo age in days (e.g., 3 or 5) is subtracted from the transfer date to determine the equivalent oocyte retrieval date.
References
- American College of Obstetricians and Gynecologists (ACOG). Committee Opinion No. 700: Methods for Estimating the Due Date. Obstet Gynecol. 2017.
- Salomon LJ, et al. ISUOG Practice Guidelines: ultrasound assessment of fetal biometry and growth. Ultrasound Obstet Gynecol. 2019.