Pregnancy week by week — your first-trimester guide
This pregnancy week by week guide starts at week 4 — around a missed period — and walks through week 12, the close of the first trimester. Each page covers baby size, how your body may feel, a short checklist, and when it is worth talking to your midwife or doctor. Daily tips live in the BabyPath app; this site is for reading, sharing, and your account.
How pregnancy weeks are counted
Pregnancy is usually dated from the first day of your last menstrual period, not from the day you conceived. That can feel confusing. If you have a fairly regular cycle, conception often happens about two weeks after that first day. So at “4 weeks pregnant,” the embryo has often been growing for about two weeks.
Your due date is an estimate. Many people get a clearer date at a first ultrasound — often called a dating scan — sometime between about 8 and 14 weeks. The scan measures the baby from the top of the head to the bottom of the rump (crown–rump length). If your cycles are irregular, you conceived with fertility treatment, or you are not sure of your dates, your clinician will help you place the week.
Weeks are grouped into trimesters. The first trimester is commonly weeks 1–12. The second trimester often starts at week 13. Different clinics draw that line in slightly different places. What matters more than the label is that early pregnancy is a time of fast development — and a time when rest, food, and prenatal care do a lot of quiet work.
What you will find on each week page
Every week page follows the same shape: baby development with length in mm or cm, how you may feel, a 3–5 item checklist, when to talk to a clinician, a short BabyPath note, and a small FAQ. Fruit comparisons appear only when official sources agree.
Weeks 4 to 12 at a glance
- 4 weeks pregnant — about 2 mm. Implantation, a possible home test, and the first quiet body shifts.
- 5 weeks pregnant — still tiny (about 2 mm). The neural tube and early heart are forming. Many people take a test this week.
- 6 weeks pregnant — about 6 mm, often compared to a pea. Limb buds appear. Nausea may start in earnest.
- 7 weeks pregnant — about 10 mm, often compared to a grape. Extra blood volume, thirst, and a womb that may feel like a lemon.
- 8 weeks pregnant — about 1.1–1.6 cm. A good week to book prenatal care if you have not already. Dating scans are often offered from around now.
- 9 weeks pregnant — about 1.6–2.2 cm. Hormones may feel loud. The face is becoming easier to recognise on a scan.
- 10 weeks pregnant — about 3 cm. Booking appointments are common. Bloating and heartburn may join the list.
- 11 weeks pregnant — about 4.1–5 cm. The placenta is taking over more of the work. Scan prep belongs on your list.
- 12 weeks pregnant — about 5.4–6.1 cm, often compared to a plum. The first trimester is winding down. Many people choose this week to tell work or a wider circle.
Weeks 13–40 will follow after this batch is approved.
What the first trimester often feels like
The Office on Women’s Health notes that hormones in the first trimester can affect almost every system in your body. You might notice a missed period, sore breasts, nausea (at any time of day), food aversions, mood changes, constipation, peeing more often, headaches, or heartburn. You might also feel fine. Both can be normal.
Tiredness is very common. So is feeling more emotional than you expected. If this is your first pregnancy, you may not look pregnant until around week 12. If you have given birth before, you may show sooner.
A few habits are worth starting as soon as you know:
- Folic acid. Health services such as the NHS advise 400 micrograms of folic acid each day until at least week 12, and many prenatal vitamins continue after that. Ask your clinician what is right for you.
- You do not need to eat for two. A balanced pattern with fruit, vegetables, and regular fluids is the usual advice. There are some foods to limit or avoid in pregnancy — your midwife or doctor can walk through the list for your country.
- Alcohol, smoking, and extra caffeine. Most clinicians will ask you to stop alcohol and smoking and to go easy on caffeine. Ask for help if that is hard.
This guide will not replace prenatal care.
How BabyPath fits next to this guide
BabyPath is a pregnancy and early-parenthood companion. The full guided experience is in the app. The website is for reading, sharing links, your registry, weekly digest pages (if you have Plus), and account access.
On the free plan you get 2 daily tips, a 3-item daily checklist, Ask AI in the app (3 questions a day), Letter to Baby for the current week, a registry of up to 10 items, and coparent access so a partner can share the same list and tips. BabyPath Plus is EUR 3.99 a month or EUR 29.99 a year and adds 5 tips a day, 20 Ask AI questions a day, the letter archive, weekly digests, and an unlimited registry.
These week pages are not the same as the short weekly digest cards already on /en/digest/.... Digests are a Plus recap. These articles are the public week-by-week reference.
Frequently asked questions
When does the first trimester end?
Many guides, including this one, treat weeks 1–12 as the first trimester and week 13 as the start of the second. Some clinicians talk about the first trimester lasting through week 13. The shift is gradual. Energy and nausea often ease over several weeks, not on a single date.
Why do baby sizes differ from site to site?
Length is usually crown–rump length, and sources measure at the start of a week, the end of a week, or as an average. Fruit pictures are informal. We give a range when official sources disagree and we skip a fruit if they do not agree.
Is this medical advice?
No. BabyPath is not a medical device. These pages are general information. Always talk with a midwife, GP, or obstetric clinician about your own pregnancy.
Browse the weeks
Week 4 · Week 5 · Week 6 · Week 7 · Week 8 · Week 9 · Week 10 · Week 11 · Week 12
Disclaimer
BabyPath is not a medical device. This guide is general information, not personal medical advice, diagnosis, or treatment. Development timing and symptoms vary. Talk with a qualified clinician or midwife about your care.