Week 1 of 40

First trimester

What's happening with the baby

In week 1 there is no baby yet, and you aren't pregnant. Pregnancy is counted from the first day of your last period, not from the day you conceive. Conception usually happens around two weeks later, so weeks 1 and 2 are counted as part of the 40 weeks even though they come before conception. ACOG's guide to fetal growth and Mayo Clinic's first trimester guide both explain the count this way.

This is why your due date is worked out from the first day of your last period. If that date is uncertain, an early ultrasound may be used to estimate it instead, as ACOG describes.

What you might notice

Week 1 is your period. Your body is shedding the lining of the uterus from the last cycle and getting ready to release an egg later in this cycle. There are no pregnancy symptoms at this stage, because there is no pregnancy yet.

It's worth noting the date your period starts. It's the date a doctor or midwife will usually ask for, and the one our calculators use.

Things worth doing

Folic acid. If you're trying to get pregnant, the usual advice is 400 micrograms (400 mcg) of folic acid a day, ideally starting about 3 months (12 weeks) before you start trying and continuing through the first 12 weeks of pregnancy. Some people need a higher dose, so check with your doctor or midwife if you're unsure. See the NHS vitamins page and healthdirect's pregnancy planning guide.
A check-up before trying. A pre-pregnancy check-up looks at your health, medicines, past pregnancies and vaccinations. ACOG's pre-pregnancy care FAQ explains what's covered, and healthdirect suggests seeing your doctor a few months before you start trying.
Medicine check. If you take regular medicine, talk to your doctor before trying, and don't stop anything on your own. The NHS medicines-in-pregnancy page is a good place to start.
Alcohol and smoking. There is no known safe amount of alcohol in pregnancy, and the NHS suggests not drinking if you're trying to get pregnant. If you smoke, the NHS stop smoking in pregnancy page explains the risks and where to get support to quit.

For partners this week

Talk together about timing, money, work and support, if you haven't already.
If you smoke or drink heavily, this is a good time to cut down or stop too. It makes it easier for both of you.
Offer to come along to a pre-pregnancy check-up, if that's wanted.

When to get help

See a doctor before trying to get pregnant if you:

have a long-term health condition, such as diabetes or epilepsy, or take regular medicine
have had problems in a past pregnancy
aren't sure whether you need a higher dose of folic acid (the NHS lists diabetes and some epilepsy medicines among the reasons)