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Pregnancy

Pregnancy week by week

37 weeksUpdated

You are pregnant, or you think you might be, or you have known for months and are counting the days now. Whichever week this is for you, a lot is changing, for your baby and for you, and much of it happens quietly, out of sight.

Pregnancy is counted in weeks from the first day of your last period, so by the time a test turns positive you are already at week 4. It is a quirk of the calendar, and since it is the count your provider uses, it is the one used here.

Forty weeks is a long time, and it does not feel even. The first ones are quiet on the outside and busy on the inside. The middle is when it starts to feel real, with a bump and the first kicks. The last ones are slow and heavy and full of waiting, and then, one day, it is over.

Each week has its own page here: how your baby is growing, what your body is doing, what is expected, and what is worth asking about at your next visit. Start at the week you are in, or from the beginning, and come back as the weeks go by.

First trimesterWeeks 4 to 13

A positive home pregnancy test on a folded linen cloth, beside a glass of water and a sprig of dried lavender

The weeks of finding out. A line on a test, a date circled, a secret that is yours for a while. Your baby goes from a cluster of cells to a fully formed, inch-long person with a beating heart, and none of it shows: from the outside you look exactly as you did, which can make the whole thing feel strangely private.

Inside, your body is working harder than it ever has. More blood, new hormones, and for many people a tiredness like no other and a queasiness that comes and goes on its own schedule. This is also when you meet your provider for the first time, see your baby on a screen, and make the first choices about screening. By week 13 the fog usually begins to lift, and the second trimester earns its reputation.

Second trimesterWeeks 14 to 27

A pair of knitted baby socks on an open notebook with a pencil, beside a cut mango on a plate

The middle stretch, and for many people the comfortable one. Energy comes back, food tastes like food again, and the bump stops being a suspicion and becomes a fact. Somewhere between weeks 16 and 22 you feel the first movement, a flutter you are not sure of, and a few weeks later a kick that a hand on your belly can catch from the outside.

Your baby learns to hear, to taste, to open their eyes, and grows from a few inches to a length that changes how you sit and sleep. The long ultrasound around week 20 is the unhurried look at every part of them; the glucose screening comes toward the end. By week 27 they could, in principle, survive outside you, and the weeks have started to feel real in a way they did not before.

Third trimesterWeeks 28 to 40

A packed hospital bag with a folded muslin blanket on top, a small pumpkin and reading glasses on a book

The weeks of growing and getting ready. Your baby mostly gains weight now, turns head down, and settles lower into your pelvis; you get heavier, sleep worse, and find that the stairs and the bathroom are both suddenly further away. The kicks have weight behind them, and the practice contractions begin, tightening and letting go with no pattern at all.

You see your provider more often, every two weeks and then every week, and the practical things gather in these weeks: the Tdap shot, the group B strep test, the bag by the door, the car seat in the car. Week 37 is early term, week 39 is full term, and week 40 is the due date that about one baby in twenty keeps. The rest arrive on their own schedule, which is the last thing pregnancy teaches.