5 Weeks Pregnant: Baby Size, Symptoms and What to Do

Your baby this week

Still about the size of a sesame seed, your embryo is busy. The brain and spinal cord are forming quickly, and the first features of the face are taking shape. Blood vessels, the umbilical cord and the placenta are developing too.

Around week 5 the neural tube, which becomes the brain and spinal cord, is closing; that's done by about four weeks after conception. That's why folic acid matters so much right now, and why it makes sense to avoid unnecessary medicines, alcohol and smoking. The heart is a simple tube that has started to contract, though an ultrasound rarely shows it yet. Morning sickness often begins now, and despite the name it can strike at any time of day. Small, frequent meals, a few crackers before getting up and sipping fluids through the day can help. If you can't keep any fluids down, you're losing weight or your urine is dark, that may be severe vomiting (hyperemesis gravidarum), which needs treatment. Now is a good time to book your first prenatal appointment.

By the numbers

Week 5 covers days 35 to 41 counted from the first day of your last period, which is 13% of a 40-week pregnancy. About 245 days remain until a 40-week due date. By date of conception, your baby is about 3 weeks old.

Pregnancy is dated from the first day of your last period, so conception happens around week 2. Your due date is 280 days (40 weeks) from that day, and an early ultrasound may adjust it.

Your body

Early signs often show up now: tiredness, tender breasts and needing to pee more often. Nausea can start too, and despite the name morning sickness, it can hit at any time of day.

Tests and to-dos this week

Keep taking your prenatal vitamin while you wait for your first visit. Jot down the first day of your last period and any medications or supplements you take so you can share them with your provider.

No routine test falls in this exact week; your provider schedules your regular checkups.

Coming up: First prenatal visit (from week 6). Full prenatal visit schedule

Tips for the first trimester

• Take 400 micrograms of folic acid a day; your provider may advise a higher dose if neural tube defects run in your family.
• Avoid alcohol, smoking, raw or undercooked meat, fish and eggs, and unpasteurized dairy.
• For nausea, try small, frequent meals and sipping fluids; call your provider if you can't keep anything down.
• Check every medicine and supplement you take with your provider or pharmacist before continuing.

Last week and next week

Last week (4): Your baby is about the size of a poppy seed and has just settled into the lining of your uterus.

Next week (6): Your baby is about the size of a pea.

Frequently asked questions