1 Week Pregnant
You’re 1 week pregnant — in the first trimester, and 39 weeks to go until your due date. It's very early — here's exactly what's happening.
★ Week 1 is your last period — conception is still ~2 weeks away.
How big is your baby at 1 week?
There’s no measurable baby yet at week 1. Pregnancy is counted from the first day of your last period, so the earliest weeks happen before conception even takes place.
Sizes are averages from standard fetal-growth references. Every baby grows at its own pace — your provider tracks yours at scans.
Baby development at week 1
You're not actually pregnant yet. Pregnancy is dated from the first day of your last menstrual period (LMP), so week 1 is your period. Doctors use this convention because most people know when their last period started but not the exact moment of conception. Your body is shedding the previous cycle's lining and beginning to prepare an egg for release in about two weeks.
Your body at 1 week
Common symptoms many people notice around week 1 include:
- A normal period (this is day 1 of your cycle)
- Typical menstrual cramps
- The usual start-of-cycle mood and energy
Symptoms vary enormously from person to person and pregnancy to pregnancy. Not having a symptom on this list is just as normal as having it.
Tips for week 1
- If you're trying to conceive, start a prenatal vitamin with folic acid now
- Cut back on alcohol and smoking ahead of conception
- Note the first day of this period — it's what your due date is calculated from
What trimester is 1 week?
Week 1 falls in the first trimester. As a quick map: the first trimester runs weeks 1–13, the second covers weeks 14–27, and the third is week 28 through birth (a due date is set at 40 weeks). Want your own dates? Our Pregnancy Due Date Calculator shows your due date and exactly how far along you are today.
The first trimester (weeks 1–13) is when the baby's major organs and body systems form, and when pregnancy symptoms like nausea and fatigue are usually strongest. It's also when most prenatal care begins — the dating scan, early bloodwork, and (if you choose) genetic screening all happen in this window.
Frequently asked questions
- How many months is 1 week pregnant?
- 1 week pregnant is about 1 month. Pregnancy months don't divide evenly into 4-week blocks, so week-to-month conversions are approximate — most providers track pregnancy by week, not month.
- Is there a baby yet at 1 week?
- Not in the way you'd picture. Pregnancy is dated from your last period, so weeks 1–2 happen before conception and week 3 is when fertilisation occurs. There's no measurable baby to picture yet — but the foundations are being laid.
- What trimester is 1 week?
- Week 1 is in the first trimester. The first trimester is weeks 1–13, the second is weeks 14–27, and the third is weeks 28 to birth (around week 40).