Illustration of a baby at week 12 inside the womb in cross-section, with the placenta and umbilical cord — Womb in cross-section, enlarged to show detail. Not true size.

First trimester, week 12

12 weeks pregnant: Reflexes and the 12-week scan

Size of a: Lime
Length: 5.4 cm crown to rump
Weight: 14 g approximate
Heart rate: 140–170 bpm typical range
Due date: 196 days away 30% 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 12 weeks pregnant, your baby is about the size of a lime: roughly 5.4 cm from crown to rump, weighing about 14 g. You’re in your first trimester, with about 28 weeks to go until your due date.

Your baby this week

Reflexes are appearing. The fingers curl, the toes flex, and the mouth makes sucking movements.
The intestines, which have been growing partly inside the umbilical cord, move back into the belly.
The kidneys are producing urine, and the pituitary gland is starting to make hormones.

Your body this week

The top of your uterus has risen above your pubic bone, and a clinician may be able to feel it.
For many, energy starts to return. Sickness usually eases somewhere between 12 and 20 weeks.
Once a healthy heartbeat has been seen at this stage, the chance of miscarriage is much lower than in the early weeks.

Typical weight gain so far: 0.5–1.8 kg
Your uterus: Just above the pubic bone

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

What happens at the 12-week scan

Despite the name, the NHS offers this dating scan at around 10 to 14 weeks. It takes about 20 minutes. You may be asked to have a full bladder for a clearer picture, so check beforehand.

The scan measures how far along you are and sets your estimated due date. It also checks how many babies there are, that the baby is growing in the womb, and how they are developing. It can pick up some health conditions, such as spina bifida, but not all of them. A more detailed look comes at the 20-week scan.

The screening test at 12 weeks: what it means

You may be offered screening for Down’s, Edwards’ and Patau’s syndromes. It is your choice whether to have it. The combined test uses a blood test plus an ultrasound measurement of the fluid at the back of the baby’s neck (nuchal translucency).

The result tells you the chance of a condition. It doesn’t give a definite answer. If the chance is higher, you’ll be offered further options, which may include NIPT or a diagnostic test such as CVS. If your scan happens after 14 weeks, you’d have a different blood test between 14 and 20 weeks, which is not quite as accurate.

Can you tell the gender at 12 weeks?

Not reliably. Some sonographers will guess from the angle of the genital “nub”, but it isn’t diagnostic and many won’t say. See how accurate nub theory really is, or compare every way to find out.

Is it safe to tell people after 12 weeks?

Many people wait until after this scan, partly because most miscarriages happen before about 13 weeks. No week carries a guarantee, and there’s no medical rule about when to share your news. Some people want support around them earlier, and that’s just as reasonable. For work, see when you have to tell your employer.

Scans, tests and checkups

This week

NIPT (cell-free DNA blood test) Blood test
A blood test that screens for Down syndrome (trisomy 21), trisomies 18 and 13, and can report sex chromosomes. It is a screening test. A high-chance result is confirmed with CVS or amniocentesis.

Baby’s sex: Sex from ~10 weeks, typically >98–99% accurate
This week

CVS (chorionic villus sampling) Diagnostic
Diagnostic test on a tiny placenta sample, offered after a high-chance screening result or known family condition. The NHS gives the miscarriage risk as less than 1 in 200 for most pregnancies. The UK usually does it at 11–14 weeks.

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

NT scan / 12-week scan Ultrasound
Measures the fluid at the back of the baby’s neck (nuchal translucency). Combined with blood hormones, it estimates the chance of chromosomal conditions. The window is about 11 weeks to 13 weeks 6 days.
From week 15

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.
From week 15

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

See the full scan and test timeline

Real size, next to an adult hand

Adult hand 18.5 cmbaby 5.4 cm

Growth curve

Typical weight by week: WHO median from week 20, approximate before that. Healthy babies vary widely.

When to call your midwife or doctor at 12 weeks

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

Vaginal bleeding, with or without cramps.
Strong pain low on one side of your belly, pain at the tip of your shoulder, or feeling faint. These can be signs of an ectopic pregnancy, which needs urgent care.
Being sick so often that you can’t keep fluids down for a day.
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

Many people share their news around now, after the 12-week scan. There’s no right time. Share when it feels right for you.

Myth or fact?

Is the nub theory accurate at 12 or 13 weeks?

Partly true

It can be fairly accurate at 12–13 weeks in experienced hands, but it is an educated guess, not a diagnosis.

Read the evidence

Common questions at this stage

All common questions

More myths around week 12

Questions people ask about week 12

Can you see the gender at the 12-week scan?

Sometimes a sonographer can make an educated guess using the angle of the genital “nub”, but it isn’t diagnostic. Many clinics won’t say. NIPT (from 10 weeks) or the anatomy scan (18–22 weeks) are far more reliable.

How big is the baby at 12 weeks?

About 5.4 cm from crown to rump and 14 grams, roughly the size of a lime.

References

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.

Second trimester Weeks 14–27

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

Third trimester Weeks 28–40

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