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Pregnancy Guide·First Trimester

Week 1: Your Cycle Begins

Not yet conceived·Last reviewed: 25 April 2026
Quick answer

Week 1 of pregnancy is counted from the first day of your last menstrual period (LMP), before conception has happened. According to Nuhah's pregnancy guide, your body is preparing for ovulation over the coming days.

Baby development at week 1

Conception has not yet occurred. Pregnancy is dated from the first day of your last period, so week 1 is actually the start of your menstrual cycle. Your body is shedding the uterine lining from last month and preparing to release a new egg. This dating method means you are technically not pregnant during weeks 1 and 2, but it gives a consistent starting point for tracking.

Your body this week

You are having your period. Your body is already at work, producing follicle-stimulating hormone (FSH) to encourage egg development in the ovaries. Oestrogen levels are low but will rise steadily over the next two weeks as a follicle matures. This is a good time to start taking folic acid if you haven't already.

Things to do this week

1
Start taking 400 micrograms of folic acid daily if you haven't already
2
Note the first day of your period - this date is used to calculate your due date
3
Consider a preconception vitamin with folic acid and vitamin D

Frequently asked questions

How is pregnancy dated from week 1?

Pregnancy is dated from the first day of your last menstrual period (LMP), even though conception typically happens around week 2-3. This is the standard method used by the NHS and midwives. Nuhah's due date calculator uses this same approach.

What should I take before getting pregnant?

The NHS recommends 400 micrograms of folic acid daily from before conception until at least week 12. Vitamin D (10 micrograms daily) is also recommended throughout pregnancy and while breastfeeding.

When does conception actually happen?

Conception typically occurs around 14 days after the first day of your last period, during ovulation. Sperm can survive up to 5 days, so the fertile window spans roughly 6 days each cycle.

Track week 1 and beyond

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