Pregnancy Week by Week for Dads Without the Fruit Sizes

Nine months, right? Close. Doctors count pregnancy in weeks, 40 of them, and they start counting before your baby even exists. Welcome to the first of many things that make perfect sense to everyone except you.

Most week-by-week guides tell you the baby is the size of a lime. Useful if you’re a fruit stand. This is pregnancy week by week for dads: what’s happening and what to actually do about it, one trimester at a time.

How are pregnancy weeks counted?

Pregnancy is counted from the first day of her last period, not from conception. So by the time you see a positive test, she’s usually already four or five weeks pregnant.

The 40 weeks split into three trimesters:

Trimester	Weeks	In one line
First	1 to 13	Hardest for her, invisible to everyone else
Second	14 to 27	The good stretch: energy back, bump showing
Third	28 to 40	Big belly, little sleep, bag by the door

Or, shorter. Trimester 1: tired. Trimester 2: better. Trimester 3: everything is a negotiation.

Pregnancy week by week for dads: weeks 1 to 13

The baby: the brain, spine and heart start forming in the first eight weeks. By week 12, the kidneys are already making urine and fingernails are forming, according to ACOG. All of that in something about the size of a golf ball.

Her: this is often the roughest stretch. Nausea, exhaustion and mood swings hit hard, and since she isn’t showing yet, nobody gives her a seat on the train. She’s growing a placenta from scratch. Tired is an understatement.

Your job:

• Pick up the slack at home: groceries, cooking, cleaning, a bit more than usual. This is the stretch you’ll be remembered for.
• Go to the first prenatal visit and the first ultrasound.
• Keep snacks within reach. Plain crackers have saved more mornings than you’d think.
• Agree on who to tell, and when. Many couples wait until around week 12.

Just found out? Start with your first month as a dad-to-be. And our first trimester guide goes deeper on how to support her.

Second trimester for dads: weeks 14 to 27

The baby: bones harden, hearing starts to develop, and by week 20 the ears, nose and lips show up on an ultrasound. Between weeks 21 and 24 the kicks get stronger. Around week 26, the eyelids can open and close.

Her: for most women, this is the best part. Energy comes back, nausea usually fades and the bump appears. She’ll start feeling movement somewhere around weeks 18 to 22. You’ll usually feel a kick from the outside a few weeks later, often around week 24. It may stop the second your hand lands. Babies have timing.

Your job:

• Be there for the anatomy scan around week 20. More on that below.
• Talk to the bump. Your lower voice carries well, and by the third trimester the baby can hear you. It feels ridiculous. Do it anyway.
• Start on the big stuff: gear you actually need, a birth class and the paternity leave conversation with your boss. Our guide on how to ask for paternity leave has a script.
• Plan a babymoon. It might be your last trip without a tiny, loud travel companion. Make it count.

What’s happening at 20 weeks pregnant?

Week 20 is the halfway point, and the week of the anatomy scan. It’s a detailed ultrasound, usually between weeks 18 and 22, that checks the baby’s organs, growth and position, plus the placenta. It’s also when many couples find out the sex, if they want to know.

By now, the part of the baby’s brain that controls movement is fully formed and the digestive system is working. The baby is doing far more acrobatics than she can feel.

Your job at 20 weeks: clear your calendar, sit next to her and ask questions. If the sonographer goes quiet for a while, they’re measuring tiny things very carefully. That’s normal.

Third trimester for dads: weeks 28 to 40

The baby: the lungs start making surfactant, the stuff they need to breathe after birth. The baby can startle at loud sounds, sense light and grasp. Somewhere between weeks 33 and 36, most babies turn head-down for the birth. The last weeks are mostly about putting on fat to stay warm on the outside.

Her: big belly, bad sleep, a bladder that has formally resigned. Visits to the doctor now come every two weeks, then weekly from week 36.

Your job:

• Install the car seat and get it checked. Here’s how to install an infant car seat.
• Learn how to tell if she’s in labor and what your role is in the delivery room.
• Pack the hospital bag by week 36 to 38, and keep the car fueled.
• Sort the money: add up what’s coming with our baby cost guide, and know how to add the baby to your health insurance.

How accurate is the due date?

Not very. The due date marks 40 weeks, but only a small share of babies, often quoted as about 4 in 100, arrive on the day itself. A pregnancy counts as full term from 39 weeks to 40 weeks and 6 days, and anything from 37 weeks is early term. First babies often take their time and arrive a little after the due date. Plan for a window, not a date.

Pregnancy week by week chart: printable timeline poster

Our free pregnancy poster puts all 40 weeks on one page, so you can tick them off together and see what’s coming next. Hang it somewhere you’ll both see it. The fridge works. So does the back of the bathroom door, where she’ll be spending a lot of time.

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General information, not medical advice. Every pregnancy is different. Her care provider will tell you what’s normal for her.

Sources: ACOG: How Your Fetus Grows During Pregnancy, March of Dimes: What is full term?.