Your First Trimester, Week by Week

The short answer: The first trimester runs from week 1 to week 13, counted from the first day of your last period. In these weeks your baby grows from a ball of cells into a fully formed tiny body with a beating heart, arms and legs. Most of what you feel, the sickness, the deep tiredness, the sore breasts, comes from hormones and is normal. Feeling sick usually peaks between 8 and 12 weeks and settles by 16 to 20 weeks. This guide walks you through what is happening inside, week by week, and what is normal at each stage.

This post is about what is happening in your body. For the practical side, which appointment to book, which tests happen when, and what is safe to eat and do, read my companion guide on your first trimester care plan and checklist.

How are the weeks counted?

This confuses almost everyone, so let me clear it up first. Pregnancy is counted from the first day of your last period, not from the day you conceived. That means in weeks 1 and 2 you are not actually pregnant yet. Ovulation happens around week 2, and conception around week 3.

So when a scan says you are 8 weeks pregnant, your baby has been growing for about 6 weeks. Nothing is wrong; that is just how doctors count everywhere in the world. If you are not sure of your dates, my free due date calculator will work it out from your last period.

What is happening week by week?

Here is what your baby is building, month by month, through the first trimester.

Two things are worth pausing on. First, by six to seven weeks the heart is already beating in a regular rhythm, which is often what you see on that first scan. Second, and this is the important one: almost all of your baby's main body parts are being built in these first three months. The brain and spinal cord, the heart, the limbs, the eyes and ears are all being formed in these weeks, before the fetal stage begins at the end of week 10.

That is exactly why I ask you to check with me before taking any medicine in early pregnancy, even a tablet you have taken safely for years. It is not me being over-cautious. It is that this is the building phase.

When will I feel each symptom?

Symptoms arrive on their own schedule and vary hugely between women. Some women feel almost nothing in the first trimester, and that is normal too; it does not mean anything is wrong.

What you notice	When it usually starts	What it feels like
Missed period	Around week 4	The earliest and most reliable sign
Feeling sick	Around 4 to 6 weeks	Any time of day or night, not only morning
Tiredness	Early, especially the first 12 weeks	A heavy, unusual exhaustion from hormone changes
Breast changes	Early weeks	Larger, tender, tingling; veins show, nipples darken
Passing urine often	Early weeks	Including waking at night
Taste and food changes	Early weeks	A metallic taste; cravings, or going off foods you loved
Constipation	Early weeks	Common and uncomfortable, not dangerous
More discharge	Early weeks	Normal if there is no itching, soreness or burning

I have deliberately not put percentages next to most of these. Good sources list them as common without counting them, and I would rather tell you honestly that we do not have a reliable number than invent one.

How long does the sickness last?

Feeling sick affects somewhere between half and eight in ten pregnancies, and about half of women actually vomit. It usually starts soon after the missed period, peaks between 8 and 12 weeks, and improves as you move into the second trimester. For most women it has cleared by 16 to 20 weeks.

The reassurance I most want you to hear: feeling sick does not harm your baby. Many women in my clinic worry that if they cannot eat properly, the baby is starving. In these early weeks the baby is still extremely small, and it takes what it needs. Eat what stays down and do not add guilt on top of nausea.

There is a more severe form, called hyperemesis gravidarum, which affects roughly three in a thousand to three in a hundred pregnancies. It causes dehydration and weight loss, and it sometimes needs treatment in hospital. This is not something to simply endure quietly. If nothing is staying down, tell me.

Is spotting in early pregnancy normal?

Some early bleeding is common and often turns out to be nothing. Around the time the pregnancy settles into the womb lining, some women have what is called implantation bleeding, which is like a very light period. In fact a period that is much lighter than usual can itself be an early sign of pregnancy.

But here is my rule, and I want it to be clear: bleeding in pregnancy is never something to sit at home and wonder about. Most of the time I will check and reassure you. Tell me the same day. And go straight to hospital, not tomorrow, if the bleeding is heavy, meaning you soak through a pad soon after putting it on, or if it comes with strong pain, pain at the tip of your shoulder, or feeling faint.

Should I be worried about miscarriage?

I would rather answer this honestly than leave you searching at 2am.

Miscarriage is more common than most families admit to each other. In one large study of over 400,000 pregnancies, about one in eight recognised pregnancies ended in miscarriage. Risk is lowest for women in their late twenties and rises after 35. Those numbers come from a European study, so treat them as the general picture rather than an exact figure for India.

The part I most want you to hear: it is almost never caused by anything the mother did. Not lifting something, not eating the wrong food, not a stressful day at work, not something a relative told you was your fault. One important exception: a significant fall or a blow to your tummy is not the same as ordinary daily activity. If that happens, get checked the same day, and go to hospital straight away if you have pain, bleeding, or feel faint. Most early miscarriages happen because the pregnancy was not developing correctly from the start, and nothing you did or avoided would have changed it.

The main sign is vaginal bleeding before 24 weeks, often with cramping pain low in your tummy. If that happens, it does not automatically mean you are losing the pregnancy. It means you need to be seen.

Your questions, answered

I do not feel pregnant at all. Is something wrong?

Almost certainly not. Symptoms vary enormously, and some women sail through the first trimester feeling completely normal. Strong symptoms are not a sign of a healthier pregnancy, and mild ones are not a warning. Your scan and your check-ups tell us how things are going, not how rough you feel.

My sickness stopped suddenly at 10 weeks. Should I panic?

No. Sickness commonly eases as you approach the second trimester, and it can settle over a few days rather than gradually. If it disappears along with bleeding or pain, get checked. On its own, it is usually just the hormone pattern shifting.

Can I keep doing my housework and going to work?

Yes. Normal daily activity, cooking, cleaning, walking and going to work are all fine in an uncomplicated pregnancy, and staying active is good for you. Rest when you are tired, and do not lift anything that genuinely strains you. If your work involves heavy physical strain, chemicals, or long night shifts, talk to me about your particular situation.

Everyone is telling me to eat for two. Should I?

No. In the first trimester you need almost no extra calories, and the advice to eat double is one of the most common ways women gain more weight than is helpful. What matters far more in these weeks is the quality of what you eat and your folic acid. My pregnancy diet guide sets out what actually changes.

Is the baby's heartbeat supposed to be visible at 6 weeks?

Cardiac activity can usually be detected around six weeks, and a regular rhythm is described by six to seven weeks. But dating is often out by several days, especially if your cycles are irregular. Not seeing it at a very early scan frequently just means it is early, and a repeat scan a week or two later is the usual next step.

What happens after 13 weeks?

You move into the second trimester, which most women find much easier. Sickness settles, energy returns, and the detailed anomaly scan follows, at around 18 to 22 weeks in Indian practice. My month-by-month pregnancy guide continues the story from here.

Sources for this article (8)

1. MedlinePlus, US National Library of Medicine: Fetal development (accessed July 2026)
2. NHS: Signs and symptoms of pregnancy (accessed July 2026)
3. NHS: Vomiting and morning sickness in pregnancy (accessed July 2026)
4. Hyperemesis Gravidarum, StatPearls, NCBI Bookshelf, National Institutes of Health (accessed July 2026)
5. Magnus et al., Role of maternal age and pregnancy history in risk of miscarriage, BMJ, 2019 (accessed July 2026)
6. NHS: Miscarriage (accessed July 2026)
7. NHS: Ectopic pregnancy (accessed July 2026)
8. NHS: Ultrasound scans in pregnancy (accessed July 2026)

This article is for your information and learning. It is not a substitute for a consultation. For advice about your own health, talk to me or your own doctor.