How pregnant am I?

How do I work out how many weeks pregnant I am?

To calculate how many weeks you are, take the date of the first day of your last period (medical staff might refer to this as the day of your LMP – last menstrual period) and count forward from there. Pregnancy usually lasts from 37 weeks to 42 weeks, so if you count 40 weeks from your LMP, that's your estimated due date (unless you're told otherwise).

The easiest way to work this out is to use a pregnancy due date calculator, which does the counting for you.

How pregnant am I in months?

The 40 weeks of pregnancy obviously translate into 10 “cycles” or lunar months, rather than nine. It's only in terms of calendar months that there are nine months in pregnancy. So you need to work it out that way. If the first day of your last period was 20 March, you're three months on 20 June, six months on 20 September, and so on.

Why does my pregnancy test say I'm two weeks more pregnant than I am?

You would not be the first woman to be very confused when taking a pregnancy test two weeks after ovulation and finding the digital display reads “3-4 weeks pregnant”. It's hard to know exactly when the egg was fertilised as it can happen more or less immediately – or take a few days. And most women don't know exactly when they ovulated either. For that reason, your pregnancy is considered to have begun at the start of your last menstrual cycle. Yes, that's about two weeks before sperm met egg. Mad, but a simple way to work it out.

If you've been tracking ovulation using basal body temperature or other methods, and are sure you know when that happened, you can always count forward 40 weeks from there and add two weeks on the end, for a slightly more accurate result.

If my periods aren't regular is my due date right?

The calculators and “calendar” methods of working out your due date are based on your menstrual cycle being a regular 28 days, so if you have a much longer cycle, it could be a bit out. Don't worry too much though because at your dating scan when you're around 12 weeks the sonographer will be able to give you a much more accurate indication in weeks of how far along you are.

I'm in my fifth week of pregnancy – am I four weeks pregnant or five weeks?

Four. The weeks in pregnancy work the same way as birthdays. So when you reach the end of your fifth year, you turn five years old. All the way through that fifth year up to your birthday, you're four.

Once you know which week you are in, use our pregnancy calendar to find out what you can expect from your baby and body each week till your due date, as well as when you'll have antenatal appointments and other things to think about in each stage of pregnancy.

Will midwives go with my dates or my scan dates?

The scan date will be used to determine your due date because it does usually give a very accurate picture. The scan is done between 10 weeks and 13 weeks plus six days of pregnancy and the way the baby has developed at this stage gives a lot of information about how far along you are.

If you're absolutely convinced that date is wrong, ask for this to be recorded in your pregnancy notes. It might just give you a bargaining chip towards the end of pregnancy if you're being guided towards an induction because the hospital thinks you're 41 weeks but you think you’re only 39+4, for example.

“If you ovulate late and have a long cycle, your baby might not measure properly for the dates of your last period. I track my cycles fairly closely and had to go for quite a few early scans because of bleeding, and each time when we went into the scan room I would say to them, 'I know my last period was on X date, but I didn't ovulate until CD 21 so I'll be measuring smaller than expected'. That would usually be met with a slightly amused expression and a 'let's just see what the scan says, shall we?' And each time baby would measure perfectly for my dates.”

Which trimester am I in?

Pregnancy is split into three “terms”. The first trimester lasts from week one up to the end of week 13; the second trimester from week 14 up to the end of week 27 and the last trimester from week 28 until birth.

How accurate is my due date?

Your due date is really only an estimate – so don’t book any taxis to the birthing centre or pack your hospital bag according to your EDD.

Only around 5% of babies arrive on their due date but almost all arrive within a week either side of it. The only way to tell if your baby’s arrival is imminent is to look out for the signs of labour.