OB Wheel

6 weeks pregnant: baby size, symptoms and what to expect

At 6 weeks pregnant you’re in the first trimester, about four weeks after conception. Many people have only just found out. The embryo is tiny but developing fast, and early symptoms such as nausea and tiredness often start around now.

TrimesterFirst
Month of pregnancyMonth 2
Baby is about the size ofa lentil — about 5.0 mm
Weeks to go (to 40)34 weeks

Your baby at 6 weeks

  • The embryo is about 5–6 mm long from crown to rump — roughly the size of a lentil or a pea.
  • Small limb buds are forming that will become arms and legs, with tiny dents where the ears will be.
  • A bump shows where the heart is developing and a bulge where the head will be. The brain, liver and musculoskeletal system are developing.
  • On a vaginal (transvaginal) scan, a heartbeat can sometimes be seen from around now, but most people won’t have a scan this early unless there’s a reason, such as IVF.

See how your baby grows week to week on the baby size by week chart.

Your body at 6 weeks

  • Nausea and vomiting (“morning sickness”) — often worst on waking but possible at any time of day.
  • Tiredness, sore or tender breasts, a metallic taste, and needing to pee more often.
  • A stronger sense of smell, new food likes and dislikes, mood swings, bloating and mild period-like cramps.
  • Light spotting can happen, but any bleeding should be checked by a doctor or midwife.

Appointments and things to do

  • Contact your doctor or midwife to arrange your first (booking) appointment, which usually happens between 8 and 12 weeks.
  • The dating scan is usually offered between 8 and 14 weeks.
  • Keep taking folic acid — 400 micrograms a day until at least 12 weeks.
  • If you take regular medicines for a long-term condition, tell your doctor you’re pregnant, but don’t stop them without advice.
When to get help. Get urgent medical help if you have heavy bleeding, severe pain on one side of your lower tummy, pain in the tip of your shoulder, or feel faint — these can be signs of an ectopic pregnancy. Contact your doctor or midwife if you’re vomiting so much you can’t keep fluids down.

Working out your dates

“6 weeks pregnant” is counted from the first day of your last period, not from conception, which is about two weeks later. If you’re not sure exactly how far along you are, the gestational age calculator gives the exact weeks and days, and the OB wheel shows your due date and every milestone. For which trimester and month you’re in, see the trimester calculator and the weeks to months converter.

Frequently asked questions

How many months is 6 weeks pregnant?

6 weeks pregnant is in month 2 of pregnancy, in the first trimester. Pregnancy months are counted from the first day of your last period.

How big is the baby at 6 weeks?

About 5–6 mm from crown to rump — roughly the size of a lentil or a pea.

Can you see a heartbeat at 6 weeks?

Sometimes. A heartbeat can sometimes be seen on a transvaginal scan around 6 weeks, but timing varies and not seeing one this early isn’t necessarily a problem. Your clinician will advise whether a repeat scan is needed.

Is cramping normal at 6 weeks pregnant?

Mild, period-like cramping is common in early pregnancy. Severe or one-sided pain, especially with bleeding, shoulder-tip pain or dizziness, needs urgent medical attention.

Sources

  1. NHS — Pregnancy week by week
  2. ACOG — Methods for Estimating the Due Date (Committee Opinion 700)
  3. NHS — Your baby’s movements
  4. Robinson HP, Fleming JE. A critical evaluation of sonar “crown-rump length” measurements. 1975
  5. Hadlock FP et al. In utero analysis of fetal growth: a sonographic weight standard. Radiology 1991

Last meaningfully updated: 2026-10-20.