Second trimester, week 16
16 weeks pregnant: Eyes on the move
- Size of a
- Avocado
- Length
- 11.6 cm crown to rump
- Weight
- 100 g approximate
- Heart rate
- 110–160 bpm typical range
- Due date
- 168 days away 40% of the way
At 16 weeks pregnant, your baby is about the size of an avocado: roughly 11.6 cm from crown to rump, weighing about 100 g. You’re in your second trimester, with about 24 weeks to go until your due date.
Your baby this week
- The eyes make slow side-to-side movements beneath closed eyelids.
- Toenails are starting to grow, and the scalp hair pattern is forming.
- The heart pumps an increasing volume of blood every day through a network of vessels you can see through the thin skin.
Your body this week
- Second-time parents often feel “quickening”, the first flutters of movement, between 16 and 18 weeks.
- Some people start to get backache as the bump grows and posture shifts.
- Skin changes such as darker nipples and a line down the belly (linea nigra) may appear.
- Typical weight gain so far
- 1.7–3.6 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.
Can you feel the baby move at 16 weeks?
You might. The NHS says movements are first felt somewhere between 16 and 24 weeks. In a first pregnancy you may not notice them until after 20 weeks, so feeling nothing at 16 weeks is normal. Early movements are often described as fluttering or bubbles.
If you haven’t felt any movement by 24 weeks, tell your midwife.
Should you use a home heartbeat monitor?
The NHS advises against using a home doppler. It isn’t a reliable check. You might pick up your own pulse and feel reassured when you shouldn’t be, or hear nothing and panic. If you’re worried, call your midwife or maternity unit.
What happens at the 16-week appointment
In the UK, your midwife will go through any earlier screening results, explain your next scan, and check your blood pressure and urine. It’s a good time to raise anything that has been on your mind, including your mood.
Vaccines to think about from 16 weeks
Whooping cough vaccine timing depends on where you live. The NHS says it can be given from 16 weeks and is usually given around 20 weeks, ideally before 32 weeks, though it can still be given later. In the US, it’s usually given between 27 and 36 weeks. A flu vaccine is also recommended during flu season. Ask your own team what applies to you.
Scans, tests and checkups
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This weekSecond-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 weekAmniocentesis 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
-
From week 18Anatomy 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
Real size, next to an adult hand
Growth curve
When to call your midwife or doctor at 16 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
Start sleeping on your side if it’s comfortable, and try a pillow between your knees. It becomes important advice from 28 weeks.
Myth or fact?
Does carrying high mean a girl and carrying low mean a boy?
MythNo. The shape and height of a bump depend on your muscles, body shape, how many pregnancies you’ve had and the baby’s position, not the baby’s sex.
Read the evidenceCommon questions at this stage
Questions people ask about week 16
Can you feel the baby move at 16 weeks?
Some people can, especially if they’ve been pregnant before. It feels like fluttering, bubbles or a light tapping. In a first pregnancy, you may not notice movements until after 20 weeks.
How big is the baby at 16 weeks?
About 11.6 cm from crown to rump and 100 grams, roughly the size of an avocado.
References
- NHS Best Start in Life: 16 weeks pregnant
- NHS: Your baby’s movements
- NHS: Your antenatal appointments
- NHS: Vaccinations in pregnancy
- CDC: Whooping cough vaccine recommendations
- Mayo Clinic: Fetal development, the second trimester
- 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.
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.
