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

Week 42 is in the third trimester, month 9 of pregnancy. Here's how big your baby is, what's developing, what you may feel and what to do this week.

Week 42 · 3rd trimester · month 9
About the size of a big watermelon

Your baby this week

At 42 weeks a pregnancy is considered post-term. Your care team keeps a close eye on your baby, the placenta and the amount of amniotic fluid.

From 42 weeks 0 days a pregnancy is post-term. The placenta may not support your baby as well now and amniotic fluid can decrease, so your care team monitors you closely and in most cases recommends induction or another way to deliver. This stage is uncommon, because most pregnancies end, or labor is induced, before 42 weeks. Accurate dating matters here: gestational age based on an early ultrasound is more reliable than counting from your last period. Go in right away for any change in your baby's movements, bleeding or leaking fluid.

By the numbers

Week 42 covers days 294 to 300 counted from the first day of your last period, which is 100% of a 40-week pregnancy. By date of conception, your baby is about 40 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

If labor hasn't started, you'll be closely monitored. Report any change in movement, bleeding or leaking fluid right away.

Tests and to-dos this week

Induction is generally recommended by this point. Your provider will walk you through the plan and what to expect.

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

Signs of labor: when to go in

Labor usually starts with contractions that come at regular intervals and get longer, stronger and closer together; they don't ease when you rest or change position. Your water may break with a gush or a slow trickle, and you may notice a bloody show. Agree with your provider on when to call: many practices use the 5-1-1 rule of thumb (contractions about every 5 minutes, lasting about 1 minute, for 1 hour). Go in right away for bleeding, green or brown fluid, a severe headache, constant pain or fewer movements. A contraction timer helps you track the pattern without doing the math.

Contraction timer

Tips for the third trimester

  • From 28 weeks, go to sleep on your side; if you wake on your back, just roll over.
  • Pack your hospital bag and agree with your provider on when to head in.
  • Call right away, even at night, if your baby moves less or differently.
  • Know the signs of labor: regular, strengthening contractions, your water breaking or a bloody show.

Call your provider or labor and delivery right away if you have:

  • your baby is moving less or differently than usual
  • your water breaks, especially if the fluid is green, brown or smells bad
  • bright red bleeding or constant, severe belly pain
  • a severe headache, vision changes, pain under the ribs or sudden swelling
  • intense itching, especially on the palms and soles

In an emergency, call 911.

Last week and next week

Last week (41): The average baby now weighs around 3 to 4 kg (about 6.6 to 8.8 pounds), and the big growth spurts are over.

Frequently asked questions

How big is the baby at 42 weeks?

Most babies weigh around 6.6 to 8.8 pounds (3 to 4 kg) by now. Sizes vary a lot, and growth is checked by your care team.

How many months is 42 weeks pregnant?

42 weeks is in month 9 and the third trimester. You're past your due date. Months are approximate; providers count weeks and days.

What does post-term pregnancy mean?

A pregnancy that reaches 42 weeks 0 days or more. It calls for close monitoring of your baby and the placenta, and usually induction.

Sources

Last reviewed: November 14, 2026 · Kitpebble editorial team

This page is for general information. It isn't medical advice or a diagnosis and doesn't replace your OB-GYN or midwife. Sizes are rounded averages. Our editorial policy

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