First trimester
1 weeks pregnant
Week 1 is a technicality. Pregnancy is dated from the first day of your last menstrual period, which means this week you are menstruating and not pregnant at all. The convention exists because the date of your last period is something you are likely to know, while the date of conception usually is not.
Size of
not yet conceived
Length
—
Weight
— g
Your baby at 1 weeks
There is no embryo this week. What is happening is preparation: the lining of the uterus sheds and then begins rebuilding, and a cohort of follicles in the ovaries starts maturing. One of those follicles will usually go on to release the egg that is fertilised.
If you find the counting strange, you are in good company. It means that by the time a pregnancy test turns positive, you are typically already counted as four weeks pregnant despite conception having happened around two weeks earlier.
How you may be feeling
This week feels like an ordinary period, because it is one. Cramping, fatigue, and the usual pattern of bleeding are what you would expect.
If you are actively trying to conceive, this is the week to note the start date accurately. Every dating calculation downstream — due date, gestational age, when tests are offered — is anchored to the first day of this period, and getting it right by a day or two makes everything afterwards more accurate.
Common symptoms around week 1
- Menstrual bleeding and cramping, as usual for you
- Fatigue, which is common during a period
- Mood changes tied to the hormonal shift at the start of a cycle
Appointments and tests around now
If you are planning a pregnancy, this is a sensible point to start a folic acid supplement if you have not already. Guidance generally suggests starting before conception, because neural tube development happens very early, often before a pregnancy is known.
What is normal, and what varies
Cycle length varies a great deal between people and between cycles. A cycle that is not 28 days is not a problem; it simply shifts when ovulation is likely, which is why our calculators ask for your actual cycle length rather than assuming.
Worth doing this week
Write down the date
The first day of this period is the anchor for every date that follows. Put it somewhere you will still have it in three months.
Start folic acid now rather than later
The neural tube forms very early, often before a pregnancy is detected, which is why guidance recommends starting before conception rather than after a positive test.
Note your cycle length
If you know your average cycle, dating is more accurate. If your cycles are irregular, a dating scan will matter more than any calculation.
Looking ahead
Next week your body prepares to ovulate, which is when conception actually becomes possible.
Nearby weeks
Not sure which week you are in? The week tracker works it out from the first day of your last period, and the due date calculator gives you an estimated due date.