Illustration of a baby at week 18 inside the womb in cross-section, with the placenta and umbilical cord
Womb in cross-section, enlarged to show detail. Not true size.

Second trimester, week 18

18 weeks pregnant: Listening in

Size of a
Bell pepper
Length
14.2 cm crown to rump
Weight
190 g approximate
Heart rate
110–160 bpm typical range
Due date
154 days away 45% of the way
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Checked against the sources listed on this page. Not reviewed by a clinician. Last updated 5 November 2026. How we check.

At 18 weeks pregnant, your baby is about the size of a bell pepper: roughly 14.2 cm from crown to rump, weighing about 190 g. You’re in your second trimester, with about 22 weeks to go until your due date.

Your baby this week

  • The tiny bones of the middle ear and the nerves to the brain are developing. The baby may start to detect sound around now.
  • A protective coating called myelin is beginning to form around the nerves.
  • Sex organs are well developed and can often be seen on ultrasound if the baby’s position allows.

Your body this week

  • The anatomy (anomaly) scan window opens: roughly 18–22 weeks, often 18–20+6 weeks in the UK.
  • Movements are usually first felt between 16 and 24 weeks, often after 20 weeks in a first pregnancy.
  • Feeling dizzy when standing up quickly is common, because blood pressure is naturally lower in mid-pregnancy.
Typical weight gain so far
2.5–4.6 kg
Your uterus
Between pubic bone and belly button

Weight gain range is for a pre-pregnancy BMI of 18.5–24.9 (IOM guideline). Your provider may advise differently.

Scans, tests and checkups

  • This week
    Second-trimester (quad) screening Blood test

    A blood test (AFP, hCG, estriol, inhibin-A) for chromosomal conditions and neural tube defects, if you didn’t have first-trimester screening or NIPT. The NHS offers it at 14–20 weeks.

  • This week
    Amniocentesis Diagnostic

    Diagnostic test on a small sample of amniotic fluid. Offered after a high-chance screening result. The NHS gives the miscarriage risk as about 1 in 200. A 2019 review estimated the added risk at about 0.3%.

    Baby’s sex: Diagnostic, only done for medical reasons

  • This week
    Anatomy scan (anomaly scan) Ultrasound

    A detailed ultrasound of the baby’s brain, heart, spine, face, kidneys, limbs and growth, plus the placenta position and fluid. The NHS usually does it at 18–21 weeks.

    Baby’s sex: Sex usually visible if the baby’s position allows. Ask if your hospital reports it

See the full scan and test timeline

Real size, next to an adult hand

Adult hand 18.5 cmbaby 14.2 cm

Growth curve

01 kg2 kg3 kgwk 10wk 20wk 30wk 40
Typical weight by week: WHO median from week 20, approximate before that. Healthy babies vary widely.

When to call your midwife or doctor at 18 weeks

Call your midwife, doctor or maternity unit straight away, day or night, if you have any of these:

  • Vaginal bleeding, or a gush or steady trickle of fluid.
  • Severe belly pain that doesn’t go away.
  • Regular tightenings, period-like cramps or lower back pressure that keep coming. This could be early labour.
  • Fever of 38 °C (100.4 °F) or higher, or pain or burning when you pee.
  • Pain or swelling in one leg, chest pain, or sudden shortness of breath. These can be signs of a blood clot.
  • Feeling very low, hopeless or anxious most days. If you feel you might harm yourself, get emergency help.

Based on NHS and ACOG guidance. This list isn’t complete. If something feels wrong, call anyway. In an emergency, call your local emergency number.

Tip for this week

Rise slowly from lying or sitting, stay hydrated, and keep a snack with you to prevent dizzy spells.

Common questions at this stage

All common questions

More myths around week 18

Questions people ask about week 18

Can you find out the gender at 18 weeks?

Usually, yes. At the anatomy scan the sex is often clear when the baby’s position allows, and accuracy is very high. Some hospitals don’t report sex, so ask in advance.

Can the baby hear me at 18 weeks?

The ear structures are forming, and some sound detection may begin. Clear responses to sound are usually seen from about 24–25 weeks.

References

  1. NHS Best Start in Life: 18 weeks pregnant
  2. NHS: Your antenatal appointments
  3. Mayo Clinic: Fetal development, the second trimester
  4. NHS: Your baby’s movements
  5. MedlinePlus (US National Library of Medicine): Fetal development

Advice differs between countries, so follow your own care team’s plan. Weights from week 20 are the WHO median, and earlier weights are approximate. How we check this.

All 40 weeks

First trimester Weeks 1–13

From conception to a fully formed, tiny fetus. The most rapid change of the whole pregnancy.

  1. Prenatal development at week 1 Week 1A new cycle begins
  2. Prenatal development at week 2 Week 2Ovulation — and maybe conception
  3. Prenatal development at week 3 Week 3A ball of cells finds its home
  4. Prenatal development at week 4 Week 4Poppy seed
  5. Prenatal development at week 5 Week 5Sesame seed
  6. Prenatal development at week 6 Week 6Lentil
  7. Prenatal development at week 7 Week 7Blueberry
  8. Prenatal development at week 8 Week 8Raspberry
  9. Prenatal development at week 9 Week 9Cherry
  10. Prenatal development at week 10 Week 10Strawberry
  11. Prenatal development at week 11 Week 11Fig
  12. Prenatal development at week 12 Week 12Lime
  13. Prenatal development at week 13 Week 13Lemon

Second trimester Weeks 14–27

Growth, movement and senses. Often the most comfortable stretch for parents.

  1. Prenatal development at week 14 Week 14Peach
  2. Prenatal development at week 15 Week 15Apple
  3. Prenatal development at week 16 Week 16Avocado
  4. Prenatal development at week 17 Week 17Pear
  5. Prenatal development at week 18 Week 18Bell pepper
  6. Prenatal development at week 19 Week 19Mango
  7. Prenatal development at week 20 Week 20Banana
  8. Prenatal development at week 21 Week 21Carrot
  9. Prenatal development at week 22 Week 22Papaya
  10. Prenatal development at week 23 Week 23Grapefruit
  11. Prenatal development at week 24 Week 24Ear of corn
  12. Prenatal development at week 25 Week 25Cauliflower
  13. Prenatal development at week 26 Week 26Zucchini
  14. Prenatal development at week 27 Week 27Head of lettuce

Third trimester Weeks 28–40

Weight gain, brain and lung maturation, and getting into position for birth.

  1. Prenatal development at week 28 Week 28Eggplant
  2. Prenatal development at week 29 Week 29Butternut squash
  3. Prenatal development at week 30 Week 30Cabbage
  4. Prenatal development at week 31 Week 31Coconut
  5. Prenatal development at week 32 Week 32Napa cabbage
  6. Prenatal development at week 33 Week 33Pineapple
  7. Prenatal development at week 34 Week 34Cantaloupe
  8. Prenatal development at week 35 Week 35Honeydew melon
  9. Prenatal development at week 36 Week 36Papaya (large)
  10. Prenatal development at week 37 Week 37Winter melon
  11. Prenatal development at week 38 Week 38Pumpkin (small)
  12. Prenatal development at week 39 Week 39Mini watermelon
  13. Prenatal development at week 40 Week 40Watermelon