1 week pregnant

1 week pregnant is in the first month of pregnancy. You are in week 1 of 40, in the first trimester. Here is what is happening with your baby and your body this week.

Your baby at 1 week

Pregnancy is counted from the first day of your last period, so in week 1 there is no baby yet. Your body is preparing an egg for release.

There is no embryo yet in week 1. Doctors date pregnancy from the first day of your last period because that date is easy to know, while the exact day of conception usually is not. That is why a full-term pregnancy is described as about 40 weeks, even though the baby develops for roughly 38 weeks after conception.

Behind the scenes, a new cycle is starting. Your brain releases follicle-stimulating hormone (FSH), which prompts a group of fluid-filled sacs in your ovaries, called follicles, to begin growing. Each follicle holds an immature egg. Over the coming days, usually just one of them will pull ahead and become the dominant follicle that releases an egg.

As your period ends, rising estrogen from these growing follicles signals the lining of your uterus to start thickening again, preparing a nourishing place where a fertilized egg could later implant.

Your body at 1 week

You are having your period. Your uterus is shedding its lining and getting ready to build a new one.

This week is simply your period. Bleeding usually lasts a few days, and you may have cramps, lower back ache, bloating, or feel more tired than usual. Hormone levels are at their lowest point of the cycle right now, which is why some people feel low on energy. Writing down the date your period started is useful: your doctor or midwife will use it to estimate your due date if you become pregnant this cycle. Gentle exercise, warmth on your lower belly, and rest can ease period discomfort.

Your belly at week 1

In month 1 (weeks 1–4) there is no visible change to your belly, and your uterus has barely changed size.

Belly size and shape vary a lot depending on your build, whether this is your first pregnancy, your baby's position and the amount of amniotic fluid. At checkups your doctor or midwife may measure your fundal height to track your baby's growth, and may arrange an ultrasound if the measurement is quite different from what they expect.

Symptoms at 1 week pregnant

• Menstrual bleeding
• Cramping in the lower belly
• Lower back ache
• Bloating
• Tiredness or low energy

Checkups around week 1

No pregnancy appointments yet. If you are planning to conceive, a preconception visit with your doctor or midwife is a good idea. They can review your medicines, check your vaccinations (such as rubella and chickenpox immunity), and discuss any long-term health conditions. What is offered varies by country.

Common symptoms in the first trimester

The first trimester runs from week 1 to week 13. It is when your baby's major organs, spine and heart form, and when many people feel the most tired and nauseous. Not everyone has every symptom, and it is normal for symptoms to come and go. Common ones include:

• Nausea and vomiting (morning sickness), which can happen at any time of day
• Tiredness and needing more sleep
• Tender, swollen breasts
• Needing to urinate more often
• Food aversions or cravings and a metallic taste
• Mood swings
• Light spotting around implantation

Read the full first trimester guide.

When to call your doctor or midwife

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Frequently asked questions

How big is my baby at 1 week pregnant?

Pregnancy is counted from the first day of your last period, so in week 1 there is no baby yet. Your body is preparing an egg for release.

How big is my belly at week 1 of pregnancy?

In month 1 (weeks 1–4) there is no visible change to your belly, and your uterus has barely changed size. Bump size, shape and when you start to show vary a lot from person to person.

Am I pregnant in week 1 of pregnancy?

No. Week 1 is the week of your period, before ovulation and conception have happened. Pregnancy is counted from the first day of your last period as a standard way to date it, so the first two weeks of the 40-week count take place before you are actually pregnant.

Why is pregnancy counted from my last period?

Most people know when their last period started, but very few know exactly when they ovulated or conceived. Using the first day of the last period gives doctors and midwives a consistent starting point. Your due date may be adjusted later if an early ultrasound shows the baby is measuring differently.

Should I start taking folic acid before I am pregnant?

Yes. Health authorities recommend taking at least 400 mcg of folic acid daily, ideally starting before conception. The neural tube, which becomes the brain and spinal cord, forms very early, often before you know you are pregnant. Some people need a higher dose, so talk to your doctor or midwife about what is right for you.

What trimester is 1 week pregnant?

Week 1 is in the first trimester, which covers weeks 1 to 13.

How many months is 1 week pregnant?

1 week pregnant is in the first month of pregnancy. The first month covers weeks 1 to 4. Pregnancy is about 40 weeks, or roughly 9 months, counted from the first day of your last period.

This page is general educational information and is not a substitute for advice from your doctor or midwife. Every pregnancy is different, and baby sizes are approximate averages. Last updated 2026-11-07. See our medical disclaimer.