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Trimester 1 · Week 1 of 40

Week 1 of pregnancy: The Beginning

There is no embryo yet: week 1 is your period. Why pregnancy is dated from it, when to start folic acid, and what to review before you try.

Last updated 28 September 2026

What's happening this week?

Week 1 is the week of your period. You are not pregnant yet and there is no embryo. The week is counted because doctors date every pregnancy from the first day of the last period, which is easier to pin down than the day of conception. If you are trying for a baby, this is a good moment to start a daily folic acid tablet, stop alcohol and tobacco, and check any regular medicines with your doctor. If you are only reading ahead, small steps taken now still help later.

Baby's development

There is no baby or embryo developing in week 1. Pregnancy weeks are counted from the first day of your last menstrual period, so the first two weeks of a standard 40-week pregnancy happen before conception. Your due date is set 280 days, or 40 weeks, after that first day of bleeding.

What is happening is the start of a new menstrual cycle. The womb lining that built up last month is shed as your period. At the same time, follicle-stimulating hormone (FSH) prompts several small fluid-filled follicles in the ovaries to begin growing. Each one holds an immature egg. Over the coming days one of them usually takes the lead.

This counting method explains why an app may say you are 4 weeks pregnant only about two weeks after conception. It is a convention, not a sign that anything was missed. If your cycles are long or irregular, ovulation may come later than mid-cycle, so your dates can shift once you have a scan. Measuring the embryo on a first-trimester scan is the most accurate way to confirm dates, up to about 13 weeks and 6 days.

Your baby's size

About the size of no embryo yet - your cycle is starting

0 mm

< 0.1 in · Length

Weight

Week 1

Gestational age

The size reads 0 mm because there is nothing to measure. Any fruit or seed you see attached to week 1 elsewhere is not accurate: the egg that may be released later this cycle is still inside a follicle in your ovary, far too small to see without a microscope.

Your body this week

Your period is the most obvious change. The lining of the womb is shed, and cramps, backache, tiredness and low mood can come with it, as they may in any cycle. Tracking how long your periods and cycles usually last is useful now, because that pattern is what your doctor will use to judge whether your dates are likely to be accurate.

Behind the scenes, your ovaries are already preparing the next possible ovulation as the follicles grow, and next week the womb lining will begin to thicken again.

Emotionally, the start of a cycle can bring mixed feelings, especially if you have been trying for a while. That is common. If your periods are very painful, very heavy or have become irregular, or if you have a long-term condition such as diabetes, thyroid disease, epilepsy or high blood pressure, a check with your doctor before trying can help you begin a pregnancy as well prepared as possible.

Symptoms you may notice

Every pregnancy is different - you may have some, all or none of these.

Period bleeding: This is last cycle's womb lining being shed. Use whatever pads or cups you normally use. Bleeding much heavier or longer than your usual pattern is worth mentioning to a doctor.
Cramps and backache: Common during a period. A hot water bottle and rest help many people. Pain severe enough to stop you doing normal things should be checked.
Tiredness: Blood loss and disturbed sleep can leave you drained. Regular meals that include dals, green leafy vegetables and, if you eat them, eggs or meat can help you keep your energy up.
Mood changes: Irritability or low mood around a period is common. If low mood lasts most days for two weeks or more, talk to a doctor.
No pregnancy symptoms: Nausea, sore breasts and a missed period cannot happen yet, because you are not pregnant. Anything you notice this week belongs to your normal cycle.

Medical care and tests

Folic acid tablet
Routine
Ideally 2–3 months before conception, until 12 weeks
Folic acid lowers the chance of neural tube defects, which affect the developing brain and spine and arise in the first weeks after conception, often before a period is missed. Standard advice in India, the UK and the US is 400 micrograms a day. Your doctor may prescribe a higher dose if you are at higher risk.
Pre-pregnancy review of health and medicines
Only if needed
Before you start trying
If you take regular medicines, including herbal, Ayurvedic or homeopathic products, or have a long-term condition, a doctor can review what suits pregnancy. Do not stop a prescribed medicine suddenly on your own; some conditions need steady control from the very start of pregnancy.
Thalassaemia carrier testing
Varies by provider
Before pregnancy, or at the first visit
Thalassaemia is an inherited blood disorder. An Indian expert guideline suggests testing early, with your partner tested at the same time, so you both know whether there is a chance of it affecting a baby. Availability varies, so ask your doctor whether it is offered.

Nothing in week 1 needs a hospital visit. If you are planning a pregnancy, a single pre-conception check with your doctor or at a health centre is a good time to ask about folic acid, medicines and tests.

Nutrition this week

Folate is the natural form of the B vitamin that folic acid tablets provide. Good Indian sources are palak, methi, sarson and other green leafy vegetables, plus dals, chana, rajma and nuts.
Build greens into everyday cooking: a palak dal, methi thepla or a simple saag a few times a week adds up.
Food alone is not a substitute for the tablet. Public-health advice is to take folic acid daily from before conception, because the neural tube forms very early.
Use iodised salt for everyday cooking, as Indian guidelines advise before and during pregnancy.
Alcohol has no known safe amount in pregnancy, so if you are trying, many people find it simplest to stop now rather than guess when conception happens.

Movement and exercise

If you are already active, keep going. Pregnancy guidelines recommend about 150 minutes a week of moderate activity, and building the habit before conception makes it easier to continue.
On heavy or crampy days, gentle stretching, a slow walk or restorative yoga may feel better than a hard workout.
If you might conceive soon, it is sensible to avoid saunas, hot tubs and hot yoga, because a high body temperature in early pregnancy has been linked to neural tube defects.

Things to keep in mind

Write down the first day of this period and your usual cycle length. Your doctor will ask for both.
Stop smoking and all tobacco, including gutka, khaini and paan with tobacco, and ask family members not to smoke around you. Stopping at any point helps.
Health bodies agree there is no known safe amount, time or type of alcohol during pregnancy.
If you and your partner are planning together, talk about testing for thalassaemia or other conditions that run in your families.
US guidance advises folic acid for anyone who could become pregnant, not only people actively planning.

When to contact your doctor

Call your doctor or midwife the same day if you have

Your period is much heavier or longer than usual, or you are passing large clots.
You have a fever with pelvic pain or an unusual, smelly discharge.
You have burning or stinging when passing urine.
You had a positive pregnancy test recently and now have bleeding.

Get emergency care now if you have

Bleeding that soaks a pad in an hour or less, with dizziness or fainting.
Severe tummy pain that stops you doing normal things.
One-sided lower tummy pain with shoulder-tip pain or fainting, if there is any chance you are already pregnant.
Fainting, collapse or a fit.

In India, call 108 for an ambulance, 102 for free transport for pregnant women in many states, or 112 for any emergency - or go straight to your nearest hospital with a maternity unit.

If something feels wrong, trust that feeling and call - you never need to wait for your next appointment.

Questions to ask your doctor

Is the standard folic acid dose right for me, or do I need a higher one?
Are my regular medicines suitable if I conceive?
Should my partner and I have carrier testing for thalassaemia?
Are my cycles regular enough to date a pregnancy from my last period?

Week 1 checklist

Note the first day of this period
Buy folic acid tablets and take one daily
List every medicine and supplement you use
Cut out alcohol and tobacco
Check that your salt is iodised

Frequently asked questions

Am I pregnant in week 1?

No. Week 1 is the week of your period, before ovulation and conception. It is counted because doctors date pregnancy from the first day of your last period. If conception happens this cycle, it usually takes place around the end of week 2, and a home test will not give a reliable result until about the day your next period is due.

How is a due date worked out from the last period?

The usual method adds 280 days, or 40 weeks, to the first day of your last period. This assumes ovulation happened around the middle of a regular cycle. If your cycles are longer, shorter or irregular, a first-trimester scan measuring the embryo gives a more accurate date, and your doctor may adjust your due date from it.

When should I start taking folic acid?

Ideally two to three months before you try to conceive, and at the latest as soon as you start trying. The standard dose is 400 micrograms a day, continued until the end of week 12. The neural tube closes within a few weeks of conception, often before a period is missed, which is why starting early matters. Your doctor may advise a higher dose in some situations.

This page is general information, not a diagnosis or a substitute for care from your own doctor or midwife. Pregnancies differ, and timings here are typical ranges rather than deadlines. Read our medical disclaimer and editorial policy.