What will be the gestational age on a given date after a blastocyst embryo transfer?

Gestational Age Calculation After Blastocyst Transfer

For a day 5 blastocyst transfer, add 19 days to your transfer date to establish the gestational age starting point, then count forward to your target date to determine the exact gestational age in weeks and days. 1

Calculation Method

The standard approach for assisted reproductive technology (ART) pregnancies uses the embryo transfer date plus a fixed number of days based on embryo developmental stage, not the last menstrual period. 1

Step-by-Step Algorithm

• Identify your blastocyst transfer date and determine whether it was a day 5 or day 6 transfer 1
• Add 19 days to the transfer date if you had a day 5 blastocyst transfer to establish your "gestational age zero point" 1
• Add 20 days to the transfer date if you had a day 6 blastocyst transfer instead 1
• Count forward from this adjusted date to your target date of interest 1
• Express the result as weeks plus days (e.g., 12 weeks 3 days) rather than rounded weeks for maximum clinical accuracy 1

Why This Method Is Superior

In vitro fertilization provides the most accurate gestational age assignment available, superior to both last menstrual period dating and ultrasound dating. 2

• The embryo transfer date is precisely known, eliminating recall bias inherent in last menstrual period dating 2
• Early ultrasound (performed before 24 weeks) only estimates gestational age within 5 to 14 days 2
• Do not adjust the calculated gestational age based on subsequent ultrasound measurements, as the transfer date provides superior accuracy 1

Clinical Applications

Use this precise dating for all prenatal care decisions, including timing of screening tests and anatomic surveys. 1

• Schedule aneuploidy screening based on the calculated gestational age from transfer date 1
• Time anatomic surveys according to this dating method 1
• Document both the transfer date and calculated gestational age in the medical record for clarity throughout prenatal care 1

Important Distinctions

This 19-day calculation applies specifically to day 5 blastocyst transfers; different embryo stages require different calculations. 1

• For day 2 cleavage-stage embryo transfers: add 16-17 days 1
• For day 3 cleavage-stage embryo transfers: add 17-18 days 1
• For day 6 blastocyst transfers: add 20 days 1