At 11 weeks pregnant, your baby is about 4.1 cm long, roughly the size of a fig, and the head is around half its length. This is often the week you are offered prenatal screening, and the options can be hard to tell apart.

This guide explains the tests in plain language: what each one can and cannot tell you, when it is done and how to decide whether it is right for you.

Your baby this week

The fetal period begins around now. Your baby is growing quickly, and the head makes up about half of its length. The face is more defined, with a nose, a lower jaw and ears that are moving toward their final position. The eyes are still widely spaced and shut.

Nails are forming on the fingers and toes, and hair follicles are developing. Your baby can open and close its fists, kick, and may hiccup. Bones are hardening, and the tooth buds are growing.

How it happens. The genitals are developing, but the outside appearance is not distinct enough to tell the sex on a scan yet. Most organs are already in place, and the coming weeks are largely about growth and maturing.

Your body this week

Your uterus is now rising out of the pelvis, and you may notice a firmer lower belly. Many people find their nausea begins to fade soon, while others feel it continues. Blood volume is still rising, and you may feel dizzy if you stand quickly or go for a long time without eating.

Emotions can be strong this week. Screening decisions and the wait for results are a big source of worry, and it helps to prepare for them.

Common symptoms at 11 weeks

  • A rounder lower belly. The uterus is expanding, and bloating adds to it.
  • Returning hunger. As nausea eases, many people feel hungry.
  • Dizzy spells. A drop in blood sugar or a quick rise from sitting can cause them.
  • Skin darkening. You may see a darker line or patches on the face, and these usually fade after birth.
  • Constipation and hemorrhoids. Slow digestion and pressure in the pelvis can cause both.
  • Anxious waiting. Many people feel more worried in the days before a scan or result.

Screening versus diagnosis

The first thing to understand is that screening and diagnosis are different.

A screening test estimates the chance that your baby has a condition such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18) or Patau syndrome (trisomy 13). It carries no risk to the pregnancy. The result is a probability: a "higher chance" or "lower chance" result. Neither is a diagnosis.

A diagnostic test looks directly at your baby's chromosomes. It can confirm or rule out a condition, but it involves a needle and carries a small risk of miscarriage. You are usually offered it only if a screening result or a scan suggests a higher chance, or if you have another reason.

The main screening options

What is offered depends on the country, the province or state, and sometimes on your age or health.

Combined first trimester screening. This typically combines a nuchal translucency ultrasound (a measurement of fluid at the back of the baby's neck) with a blood test that measures pregnancy hormones and proteins. In Ontario, Canada, enhanced first trimester screening is available between 11 weeks 2 days and 13 weeks 3 days. In the UK, the combined test is offered between about 11 and 14 weeks.

Non-invasive prenatal testing (NIPT). This blood test analyzes tiny fragments of your baby's DNA that circulate in your blood. It can be done from about 9 to 10 weeks. NIPT is more accurate at picking up common trisomies than older blood tests, and it can also report the sex chromosomes. It is still a screening test, so a positive result needs confirmation with a diagnostic test before any decision is made. In some places it is publicly funded for certain groups, and in others you pay for it.

Second trimester screening. If you miss the first trimester window, a blood test in the second trimester can be offered. It is less accurate than first trimester screening or NIPT.

The detailed anatomy scan. Around 18 to 22 weeks, this ultrasound checks your baby's body structures, including the heart, spine and brain. It looks for physical differences rather than testing chromosomes directly.

The diagnostic options

  • Chorionic villus sampling (CVS). A small sample of placental tissue is taken, usually between about 11 and 14 weeks. It gives an earlier result.
  • Amniocentesis. A sample of amniotic fluid is taken, usually from about 15 weeks.

Both procedures carry a small risk of miscarriage. Ask your provider for the current figure that applies where you live. These tests are optional, and the results are highly reliable.

How to decide what is right for you

There is no right or wrong choice. Some people want as much information as possible, and others prefer not to screen. It can help to think through a few questions before your appointment:

  • What would I do with the result? Would it change how you prepare, where you give birth, or what decisions you make?
  • How would I feel about a higher-chance result? Some people find the waiting and uncertainty hard.
  • Is my goal knowing, or preparing? Both are valid.
  • Who can help me decide? Your provider, a genetic counsellor and a partner can each help.

Ask your provider what is offered, what it costs, when results arrive and who will explain them. You can decline any test, and declining does not affect the rest of your care.

Your week 11 checklist

Call your provider

Call your provider if you have bleeding heavier than spotting, severe pain, a fever, or fluid leaking from the vagina. If you have a diagnostic test, follow your provider's advice about which symptoms need a call afterward. This guide is general information and does not replace medical advice.

Frequently asked questions

What is the difference between NIPT and first trimester screening?

NIPT analyzes fragments of your baby's DNA in a blood sample and is more accurate for the main trisomies. First trimester screening combines an ultrasound measurement with a blood test. Both are screening tests, and neither confirms a diagnosis.

How accurate is NIPT?

It is more accurate than older screening tests, but it is not a diagnosis. A positive result should be confirmed with CVS or amniocentesis before any decisions are made.

Do I have to have prenatal screening?

No. It is your choice. You can accept some tests and decline others, and you will still receive routine pregnancy care.

Sources

Sources: NHS: 11 weeks pregnant; Prenatal Screening Ontario: Enhanced first trimester screening; Mayo Clinic: Fetal development, the first trimester; Cleveland Clinic: Fetal development, week-by-week stages of pregnancy