Week 3 of 40
What's happening with the baby
Week 3 is usually when conception happens, around two weeks after the start of your last period. Remember that weeks 1 and 2 were counted from your last period, before you were pregnant, so "3 weeks pregnant" means roughly one week since fertilisation.
Fertilisation, when an egg and a sperm join into a single cell, takes place in a fallopian tube. Over the next few days that cell divides into a small cluster of cells as it moves down the tube towards the uterus, where it will implant. ACOG's overview and Mayo Clinic's first trimester guide walk through these first steps.
At fertilisation the single cell usually has 46 chromosomes, 23 from each biological parent. If more than one egg is released and fertilised, or a fertilised egg splits, twins can result, as Mayo Clinic explains.
What you might notice
Most people notice nothing in week 3. Your period isn't due yet, so it's too early for most pregnancy tests. The NHS pregnancy test guide says most tests are most reliable from the first day of a missed period. If you don't know when your period is due, test at least 21 days after you last had unprotected sex.
A negative result this early doesn't rule out pregnancy. If your period still doesn't come, the NHS suggests waiting a few days and testing again, and speaking to a GP if a second test is negative but your period hasn't arrived.
Things worth doing
- Keep taking folic acid. 400 mcg a day is the usual advice for the first 12 weeks, unless your doctor has suggested a higher dose. See the NHS vitamins page.
- Act as if you might be pregnant. If you could have conceived, the NHS advice is not to drink alcohol, and it's worth checking any new medicine with a pharmacist or doctor. See the NHS medicines page.
- Pick a test date. Waiting until your period is due gives a more reliable result, and saves the worry of an early negative.
For partners this week
- The wait before a test can be long. Ask how they'd like to handle it, and whether they want company when they test.
- Keep supporting the small things, like not drinking together and keeping smoke away.
When to get help
If you might be pregnant, contact a GP or urgent care service if you have a combination of:
- tummy pain low down on one side
- vaginal bleeding or a brown, watery discharge
- pain in the tip of your shoulder
- discomfort when peeing or pooing
These can be signs of an ectopic pregnancy, where a fertilised egg implants outside the uterus, usually in a fallopian tube. Symptoms usually appear between weeks 4 and 12, and you should seek advice even before a positive test. Call emergency services if you have sudden, intense tummy pain with dizziness or fainting. See the NHS ectopic pregnancy page. If you're unsure about anything, check with your doctor or midwife.