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Week 3 of pregnancy: Fertilisation

Fertilisation may happen this week. Why a test is still too early, which painkillers to choose while trying, and how to get through the two-week wait.

Last updated 28 September 2026

What's happening this week?

If you conceive this cycle, it happens around now. An egg released at the end of week 2 may be fertilised in the fallopian tube, and the new cell starts dividing as it moves towards the womb. You will not feel this, and no home or blood test can detect it yet. For now, keep taking folic acid, choose paracetamol over ibuprofen-type painkillers if you need one, and try to plan the next ten days or so so that waiting does not take over.

Baby's development

Fertilisation usually takes place in the fallopian tube, within about a day of the egg being released. When a single sperm enters the egg, genetic material from both parents combines in one cell, called a zygote. This is the true start of the pregnancy, even though the calendar says week 3. The new cell already carries the full set of genetic instructions for development.

Over the next few days the zygote divides repeatedly as it is carried along the tube. It becomes a solid cluster of cells called a morula, and then a blastocyst: a tiny hollow ball with an inner group of cells, which will form the embryo, and an outer layer called the trophoblast, which will help form the placenta. The trip to the womb takes about three to five days.

Implantation into the womb lining begins about six to ten days after fertilisation, so mostly during week 4. Until then, hCG, the hormone pregnancy tests look for, is not present in measurable amounts. That is why a test taken now is negative even when conception has happened. Once implantation is under way, hCG begins to rise quickly, and a urine test becomes reliable from around the day your period is due.

Your baby's size

About the size of a microscopic ball of cells

0.1-0.2 mm

< 0.1 in · Length

Weight

Week 3

Gestational age

At roughly 0.1 to 0.2 mm across, the blastocyst can only be seen under a microscope. The figure comes from embryology textbooks, not from any measurement in your own pregnancy, and nothing will show on a scan for a couple of weeks yet.

Your body this week

After ovulation, the empty follicle in the ovary becomes the corpus luteum, which makes progesterone. Progesterone keeps the womb lining thick and ready. It rises in every cycle, pregnant or not, which is why the days after ovulation can bring bloating, tender breasts or tiredness that feel much like the run-up to a period.

Because the same hormone is behind both, there is no reliable way to tell in week 3 whether you have conceived. Light spotting can happen for several reasons and is not proof either way. Taking your temperature, examining discharge or reading symptom lists will not settle the question before a test can.

The two-week wait between ovulation and a possible test is often the hardest part of trying. Some people want to know everything; others prefer not to think about it. Both are fine. Keeping up normal plans, work and exercise can make the days pass more easily.

Symptoms you may notice

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

No symptoms: Most people feel nothing at all in week 3. Fertilisation and early cell division do not cause physical sensations, so an absence of signs means nothing either way. Carry on with your usual routine.
Bloating or tender breasts: Progesterone after ovulation can cause these in any cycle. Loose clothing and regular meals help. On their own they are not a sign of pregnancy.
Light spotting: A small amount can happen for different reasons around this point in the cycle and does not prove pregnancy. Heavy bleeding, or bleeding with severe pain, needs checking.
Anxiety while waiting: Checking for symptoms many times a day is common and tiring. Setting a test date and keeping busy until then helps many people, and a partner or friend can share the wait.

Medical care and tests

Choosing painkillers while trying
Only if needed
Whenever needed, from now on
Paracetamol is usually the first choice if you might be pregnant, at the lowest dose that works for the shortest time. Ibuprofen, diclofenac, naproxen and pain-relief doses of aspirin are best avoided unless a doctor advises them. Many cold and pain combination products sold in India contain these, so check the label or ask the pharmacist.
Checking medicines and supplements
Only if needed
At every prescription or purchase
Whenever you are prescribed or buy a medicine, supplement or herbal product, mention that you are trying to conceive. Natural or Ayurvedic does not automatically mean safe: some products sold online have been found to contain lead, mercury or arsenic. Do not stop a regular prescribed medicine without advice.
Blood hCG test
Only if needed
Only if your doctor requests it
Very sensitive laboratory tests can pick up hCG in blood about 7 to 8 days after ovulation, and most standard blood tests about 10 to 11 days after. For most people a home urine test from the day the period is due is enough.

There is no routine test or appointment in week 3. The medicines advice above applies from now until you know whether you are pregnant, and throughout pregnancy if you are.

Nutrition this week

Iodine needs rise in pregnancy. India's health ministry advises regular use of iodised salt as a preventive measure, so make sure the salt you cook with every day says iodised on the pack.
More salt does not mean more benefit. Use iodised salt for normal cooking and keep an eye on very salty snacks, pickles and papads.
Keep eating green leafy vegetables and pulses for folate alongside your folic acid tablet; a dal and a green sabzi each day is a simple pattern.
ICMR-NIN advises taking tea and coffee between meals rather than with them, because they reduce how much iron you absorb from food.

Movement and exercise

Keep up the activity you are used to. Walking, swimming and gentle yoga are all reasonable choices.
Avoid saunas, steam rooms, hot tubs and hot yoga until you know whether you are pregnant, as overheating in early pregnancy is best avoided.
If you play contact sports or do activities with a high risk of falls, think about which ones you would stop if you turn out to be pregnant, and what you might do instead.

Things to keep in mind

Plan when you will test. Testing on or after the day your period is due gives the most reliable answer and avoids confusing early negatives.
Tell your pharmacist or doctor that you may be pregnant whenever you are given a medicine.
Stay away from alcohol and tobacco while you wait.
Line up something to look forward to in the next ten days, such as a meal out or time with friends, so the waiting does not fill every day.
If you have had a pregnancy loss before, the wait can feel especially hard. Your doctor can talk about support in a new pregnancy.

When to contact your doctor

Call your doctor or midwife the same day if you have

You need something for pain or fever and are unsure what is safe to take.
You have a fever of 38°C or more.
Passing urine stings or burns, or you need to go urgently.
You have bleeding that is unusual for this point in your cycle.

Get emergency care now if you have

Severe tummy pain, or one-sided pain with shoulder-tip pain or fainting.
Heavy bleeding with dizziness.
Fainting or collapse.

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

Which painkillers and cold remedies are safe while we are trying?
Is my regular medicine safe if I become pregnant?
When is the best day for me to take a pregnancy test?
Do I need a blood test for pregnancy, or is a home test enough?

Week 3 checklist

Mark the day your period is due
Check medicine labels for ibuprofen, diclofenac or naproxen
Keep paracetamol as your default painkiller
Take folic acid daily
Cook with iodised salt

Frequently asked questions

Can a pregnancy test be positive in week 3?

Almost never. The blastocyst has not yet implanted, and hCG, the hormone tests detect, is only made in measurable amounts after implantation begins. Even very sensitive blood tests pick it up only about 7 to 8 days after ovulation. A home urine test is most reliable from the day your period is due, and testing earlier can give a negative result even if you have conceived.

Is it safe to take painkillers while trying to conceive?

Paracetamol is generally the preferred painkiller if you might be pregnant, used at the lowest dose that works for the shortest time. Anti-inflammatory painkillers such as ibuprofen, diclofenac and naproxen are best avoided unless your doctor advises them. Many combination cold and pain remedies contain these, so read the label or ask a pharmacist before buying.

Is spotting this week implantation bleeding?

It might be, but spotting is not a reliable sign of pregnancy. Implantation mostly happens in week 4, and light bleeding can have other causes, including your normal cycle. The only way to know is a pregnancy test from the day your period is due. Heavy bleeding or bleeding with severe pain should always be checked.

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.