Trimester by trimester: what's actually happening

Pregnancy is counted from the first day of your last period, which means you are considered about two weeks pregnant at conception and around four weeks when a test turns positive. That accounting confuses almost everybody at first.

First trimester — weeks 1 to 13

Almost everything structural happens here, which is why it is the stretch where the exhaustion and sickness are worst and the least is visible.

Nausea typically arrives around week five or six, peaks near nine, and eases somewhere between twelve and eighteen. Tiredness is profound and not proportional to anything you did.

Care in this stretch is a booking appointment, bloods, and usually a dating scan. There is more about this trimester specifically in its own article.

Second trimester — weeks 14 to 27

The one people mean when they talk about the good bit. Sickness usually settles, energy returns somewhat, and the pregnancy becomes visible.

First movements arrive somewhere around 18 to 22 weeks in a first pregnancy, often earlier in later ones. The anatomy scan happens around 18 to 22 weeks, and glucose screening usually falls at the end of this stretch.

New aches begin as things stretch and shift — round ligament pain, back pain, congestion, heartburn. All ordinary, all worth mentioning if severe.

The second trimester is when most women feel human again. Use it for the things that will be hard later, including the difficult conversations.

Third trimester — weeks 28 to birth

Everything gets physically harder. Sleep becomes difficult at the exact point people start telling you to get plenty of it, which is one of the crueller jokes of the whole business.

Appointments become more frequent — usually fortnightly, then weekly. Braxton Hicks tightenings are common and are not labour unless they become regular, closer together and stronger.

This is the stretch to learn your movement pattern, because a change in it is the thing you most need to be able to notice.

Call today, at any stage

• Bleeding, or fluid leaking
• A headache that won't shift, changes in vision, or sudden swelling of face and hands
• Severe belly pain that doesn't go away
• Trouble breathing, chest pain, or a fast-beating heart
• Fever of 100.4°F or higher
• Reduced or changed fetal movement after 28 weeks — call the same day, every time, however often
• Regular tightenings before 37 weeks
• Any thought of harming yourself

Nobody minds you calling. Reduced movement in particular is something to ring about immediately rather than wait on, and it does not matter if you rang last week.

What the appointments are for

Blood pressure and urine at every visit are screening for preeclampsia, which is the reason those two unglamorous checks never stop.

Bloods early on check for anaemia, immunity and blood type. The anatomy scan checks development. Glucose screening looks for gestational diabetes. None of it is routine box-ticking — each is looking for something specific and treatable.

The part that isn't in the book

You can want this enormously and still find it long, uncomfortable and occasionally frightening. Both are allowed at once.

And you are permitted to ask questions until you understand the answer. It is your body and your baby, and an appointment is not a test you can fail.