12 weeks pregnant: baby is the size of a lime

Your baby this week

Every organ system is now in place. The kidneys work, so your baby passes small amounts of urine into the amniotic fluid and swallows some of it again. The intestines, which grew partly outside the belly, have moved inside the abdomen. Tiny fingernails have appeared, and the skeleton is changing from soft tissue into hardening bone.

How it happens. Since week 5, groups of cells have been following a genetic program that turns them into specific organs. By week 12 that first draft is complete. From here, most of the work is growth and refinement rather than building something new.

Movement is well under way. Your baby can open and close its fists, curl its toes and open its mouth. You cannot feel any of this yet because your baby is far too small to press against your abdomen. Most people first feel movement between 16 and 24 weeks.

Your baby's sex organs have formed, but most scans at this stage cannot tell you the sex reliably.

Your body this week

Your uterus is growing out of the pelvis, and some people notice a small firm bump low on the belly. Others see no change until later. Bump size depends on hormones, your pre-pregnancy weight, whether you have been pregnant before and your muscle tone, so comparing yourself to someone else tells you little.

If nausea has been a daily battle, this is often when it begins to ease. Appetite tends to come back, sometimes with a rush. The placenta is taking over the job of feeding your baby from the yolk sac, and hormone levels are settling as it does.

You may have gained little or no weight. For someone starting at a healthy weight, the first trimester usually adds about 0.5 to 1.8 kg (1 to 4 lb), and some people lose a little because of nausea. Both are common.

The 12-week scan: what it checks and what to expect

Many care systems offer a scan around this time. In the UK's NHS pathway, a dating scan is offered between weeks 8 and 14. In Ontario, Canada, enhanced first trimester screening runs from 11 weeks 2 days to 13 weeks 3 days and combines an ultrasound with a blood test.

A sonographer usually checks:

• Dates. They measure your baby from head to bottom and use that to confirm your due date. This is more accurate than counting from your last period if your cycle is irregular.
• The heartbeat. You may see it flicker on the screen.
• How many babies. The scan confirms whether you are expecting one baby or more.
• The back of the neck. This measurement, called nuchal translucency, is part of screening for conditions such as Down syndrome. It is a screening tool, not a diagnosis.

You may be asked to arrive with a full bladder for an abdominal scan, and the scan itself usually takes 20 to 30 minutes. Some clinics offer an internal scan if the baby is hard to see.

Screening tells you about probability, not certainty. A "higher chance" result does not mean your baby has a condition, and a "lower chance" result does not rule one out. If you would rather not screen, you can decline and still have the scan for dating. Ask your provider what is offered where you live, what it costs and how you will receive the results.

Why week 12 feels like a turning point

The chance of miscarriage falls significantly around now, which is why many people wait until this point to share their news. According to Mayo Clinic, about 10% to 20% of known pregnancies end in miscarriage, and most of those happen in the first trimester. Chromosome differences cause about half to two-thirds of first-trimester losses.

Mayo Clinic also says that everyday activities do not cause miscarriage. That includes exercise, sex, arguments and stress, and work without harmful chemical or radiation exposure. If you have had a loss before, week 12 may feel less like a finish line and more like one more step. That is a reasonable response, and it is fine to ask for extra reassurance or an early scan.

Deciding when to share your news

There is no right time. Some people tell close family at 4 weeks, while others wait until after the scan. It helps to decide who you would want to tell if something went wrong, because those are often the people who will support you either way.

If you work, check the rules where you live. Notice periods and protections for antenatal appointments and pregnancy-related health and safety assessments differ by country. Many people time a workplace announcement for after the 12-week scan, but you may need to tell your employer sooner if your job involves physical strain, chemicals or shifts that are hard to manage with nausea.