How is gestational age calculated after IVF?

Gestational age is counted as if it started 14 days before egg retrieval. On transfer day you are therefore 14 days plus the embryo's age: 2w 5d for a day-5 blastocyst, 2w 3d for a day-3 embryo and 2w 6d for a day-6 blastocyst.

Why am I already two weeks pregnant on transfer day?

Standard pregnancy dating counts from the first day of the last period, roughly two weeks before conception. IVF keeps the same convention so that gestational age, scan schedules and growth charts all line up with naturally conceived pregnancies.

How many weeks am I at my first scan?

The first IVF ultrasound is typically at about 6 to 7 weeks of gestation, which is roughly 3 weeks after a day-5 transfer.

Does a frozen transfer change gestational age?

No. Dating uses the embryo's age at the moment of transfer, not when it was created or frozen. A thawed day-5 blastocyst is dated exactly like a fresh day-5 transfer.

Should I use days past transfer or gestational weeks?

Both are useful. Days past transfer (DP5DT) is what clinics use in the first two weeks; gestational weeks become the standard once the pregnancy is confirmed and antenatal care begins.

What if a scan gives a different gestational age?

Most clinics keep the IVF-based dating because the transfer date is a known fact, while a scan measurement carries a margin of error. If a scan differs substantially, your clinic may re-date the pregnancy.

IVF Gestational Age Calculator

Turn your embryo transfer date into exact gestational weeks and days — on today's date or any date you choose.

Embryo transfer date

Date to check

Embryo age at transfer

Gestational age

2w 5d

0 days past a day-5 transfer (0DP5DT). Estimated due date: Wednesday, April 28, 2027.

This is an estimate for information only — only about 1 in 20 babies arrive on their due date. Always confirm dates with your midwife or doctor.

Your schedule

Milestone	Gestational age	Date
First beta hCG (typical)	4w 1d	Aug 20, 2026
First ultrasound (typical)	5w 5d	Aug 31, 2026
End of first trimester	13w 6d	Oct 27, 2026
Anatomy scan window opens	18w 0d	Nov 25, 2026
Third trimester starts	28w 0d	Feb 3, 2027
Full term	37w 0d	Apr 7, 2027
Estimated due date	40w 0d	Apr 28, 2027

Days past transfer to gestational age

Days past transfer	Day-3 embryo	Day-5 embryo	Day-6 embryo
0	2w 3d	2w 5d	2w 6d
3	2w 6d	3w 1d	3w 2d
5	3w 1d	3w 3d	3w 4d
7	3w 3d	3w 5d	3w 6d
9	3w 5d	4w 0d	4w 1d
12	4w 1d	4w 3d	4w 4d
14	4w 3d	4w 5d	4w 6d
17	4w 6d	5w 1d	5w 2d
21	5w 3d	5w 5d	5w 6d
28	6w 3d	6w 5d	6w 6d
35	7w 3d	7w 5d	7w 6d

Why IVF dating starts before the transfer

Every pregnancy, however it began, is dated from a notional last menstrual period two weeks before conception. IVF keeps that convention so that scan schedules, screening windows and growth charts all read the same as for a natural pregnancy. Practically, the rule is: gestational age on transfer day equals 14 days plus the embryo's age.

Converting between the two systems

To go from days past transfer to gestational days, add 14 plus the embryo age. To go the other way, subtract. So 9DP5DT is 14 + 5 + 9 = 28 gestational days, which is exactly 4 weeks — the point at which a period would have been missed in a natural cycle.

Comparing with a scan

If your scan gives a different age, the ultrasound due date calculator shows what date that measurement implies, and the how many weeks pregnant am I calculator works from whichever due date you settle on.

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