Week 16: Coordinated Movements

Your baby is now the size of an avocado — about 12 cm long and weighing around 100 grams — and moving with increasing coordination! The nervous system is connecting muscles to the brain, and movements are no longer random twitches but more purposeful. Many first-time parents feel their very first fetal movements around this time.

Week 16 also marks an important change in your exercise routine. According to ACOG and the NHS, it is recommended to avoid exercising while lying flat on your back after week 16, because the growing uterus can put pressure on major blood vessels and reduce blood flow to your baby. Switch to side-lying or sitting/standing exercises.

You are now four months into pregnancy, and the bump is clearly visible. The anatomy scan is getting closer, and there is much to look forward to in the coming weeks.

Baby's Development

Coordinated movements: The nervous system is developing rapidly, and your baby can now move arms and legs in a more controlled and purposeful way
Facial muscles at work: Your baby can make distinct facial expressions. While these are reflexes, the facial muscles are being trained
Toenails growing: The tiny toenails have started growing, in addition to the fingernails already in place
Nervous system maturing: The brain and spinal cord are connecting with muscles and sensory organs in an increasingly advanced network
Eyes moving: Even though the eyelids are still closed, the eyes can now move slowly from side to side
Umbilical cord stronger: The umbilical cord is now thicker and more robust, effectively transporting nutrition and oxygen between you and your baby
Skeleton continuing to harden: Calcium is actively being stored in the small bones, and the skeleton is gradually becoming harder
Size: The fetus is about 11–12 cm long (crown to rump) and weighs around 100 grams

Nervous System Development

At week 16, the brain is in a phase of rapid growth. The cerebral cortex is developing its characteristic folds (gyri and sulci). Nerve cells are connecting in an increasingly complex network, and myelination — the process by which nerve cells get an insulating fat layer — is well underway.

This development means your baby's movements are becoming more coordinated and purposeful. Your baby can now grip the umbilical cord, suck its thumb, and make coordinated kicks and turns. The nervous system will continue to develop throughout pregnancy and for several years after birth.

Your Body

First kicks: Some pregnant people can now feel the very first fetal movements. It often feels like bubbling, butterflies, or a light tickling sensation
Nausea is gone: For most people, pregnancy nausea is now a closed chapter. The second trimester is the most comfortable period
Back pain may start: As your bump grows, your centre of gravity shifts, which can cause pain in the lower back
Increased discharge: More vaginal discharge is normal and is caused by increased blood flow to the pelvic area. It should be light and odourless
Bump clearly visible: Most people now have a visible baby bump. What an exciting change!
Nasal congestion continues: Pregnancy rhinitis can last throughout pregnancy. Saline spray is safe to use
Increased blood volume: Your heart is now pumping significantly more blood than normal, and you may feel warm and sweat more easily
Skin changes: Pigmentation changes like linea nigra, darker areola, and melasma may appear or become more pronounced

Sleep Positions in Pregnancy

From weeks 16–20, ACOG and the NHS recommend sleeping on your side, preferably the left side. As the uterus gets heavier, lying on your back can put pressure on the vena cava (the large blood vessel) and reduce blood flow to your baby and the placenta.

Tips for better sleep in a side-lying position:

Place a pillow between your knees to relieve the hips
Place a small pillow under your abdomen for extra support
Use a pregnancy pillow (C-shaped or U-shaped) for full-body support
Do not worry if you wake up on your back — just turn back onto your side
Elevate your upper body slightly with extra pillows if troubled by heartburn

Good to Know

Around weeks 17–19, the anatomy scan is offered — a thorough examination of your baby's heart, brain, kidneys, and other organs. You can also find out the sex if you wish. Talk together about whether you want to know or keep it a surprise. The anatomy scan is a standard part of prenatal care.

Stretch marks may begin to appear now. They are completely common and are caused by the skin stretching rapidly. Keeping the skin well moisturised can help with itching, but a lot depends on genetic factors. Most stretch marks fade considerably from reddish to silvery white after birth.

If you feel movements, that is a great sign! But do not worry if you cannot feel anything yet. Many first-time parents do not feel clear kicks until weeks 18–22. Placental position can also affect how early you feel movements — an anterior placenta (at the front) dampens the sensation.

From week 16, it is important to adapt your exercise routine. According to ACOG, you should avoid exercises while lying on your back, because the growing uterus can press on major blood vessels. Switch to side planks, seated strength exercises, and standing exercises instead.

Exercise After Week 16 — New Guidelines

Week 16 marks a turning point for exercise during pregnancy. According to ACOG, pregnant people should avoid exercising in a supine position (lying on the back) from week 16 onwards.

Why Avoid Lying on Your Back?

When you lie on your back, the heavier uterus can press on the vena cava — the large blood vessel returning blood to the heart. This can:

Reduce blood flow to your baby and the placenta
Cause dizziness, nausea, and discomfort for you
Lead to low blood pressure

Safe Exercise Options

Standing exercises: Squats, lunges, shoulder press
Seated exercises: Bicep curls, shoulder raises, rowing exercises
Side plank: Replaces standard plank
Four-point kneeling: For back and abdominal exercises
Swimming: Excellent — the water supports your weight
Prenatal yoga: Adapted positions for the second trimester
Kegel exercises: Can be done in any position
Adapted strength training: Designed for pregnant people

ACOG still recommends at least 150 minutes of moderate activity per week. Listen to your body and reduce intensity if necessary.

The Anatomy Scan Is Approaching

Between weeks 17 and 19, the anatomy scan is offered. Here is what you should know and prepare:

Preparation

Drink some water beforehand (not too much — a partly full bladder is ideal)
Wear loose-fitting clothes for easy access to your abdomen
Write down questions you want to ask
Bring your partner — it is a special experience to share

What Is Examined

Brain and head: Size, symmetry, and development of brain structures
Heart: The four chambers, valves, and blood flow
Spine: Complete review of the vertebrae
Kidneys and bladder: Function and size
Arms and legs: Bone length, joints, fingers and toes
Placenta: Position and function
Amniotic fluid: Volume is assessed

Sex Reveal

Talk with your partner about whether you want to know the sex. Some choose to keep it a surprise until birth. Others want to know to plan and prepare. There is no right or wrong answer — do what feels right for you.

Pelvic Girdle Pain in Pregnancy

Some pregnant people begin to experience pelvic girdle pain around week 16. This is because the ligaments in the pelvis become softer and more elastic due to the hormone relaxin.

Symptoms

Pain at the front of the pelvis (symphysis pubis) or at the back at the sacroiliac joints
Pain that worsens with walking, climbing stairs, or standing on one leg
Clicking sounds or feeling of instability in the pelvis
Pain when turning in bed

What Can Help

Avoid standing on one leg (sit down to put on trousers or shoes)
Keep your knees together when turning in bed
Use a pelvic support belt
Kegel exercises strengthen the muscles around the pelvis
Swimming provides relief
Ask your midwife for a referral to a physiotherapist

When to Contact Your Midwife

Talk to your midwife if pelvic girdle pain is affecting your daily life, walking, or sleep. There is good treatment available, and early intervention gives the best results.

The Hormone Relaxin and Your Body

At week 16, your body is producing increasingly more of the hormone relaxin. This hormone plays an important role in pregnancy, but can also have some unexpected side effects.

What Does Relaxin Do?

Makes ligaments and connective tissue softer and more elastic
Prepares the pelvis to open during birth
Affects all joints in the body, not just the pelvis

Side Effects of Relaxin

Increased risk of sprains and overloading of joints
Instability and changed balance
Pelvic girdle pain in some pregnant people
Flat feet (the foot arch can drop) — many pregnant people need larger shoes

What You Can Do

Wear shoes with good support and cushioning
Avoid high heels
Be careful with exercise — avoid excessive stretching
Strengthen the muscles around the joints with adapted exercise
Kegel exercises strengthen the pelvic floor muscles

Mental Health and Preparation

Week 16 is a good time to start preparing mentally for parenthood:

Childbirth Preparation Classes

Most classes are held at weeks 28–36, but it is wise to book now as many have waiting lists
The hospital where you plan to give birth often offers classes
Check with your local hospital or community health centre
Online classes are an alternative if they suit you better

Tips for Mental Preparation

Read about birth and the postnatal period to feel more confident
Talk with friends who have children about their experiences
Start thinking about your birth preferences
Consider whether you want a childbirth preparation class together with your partner

For Partners

Place your hand on the bump and be patient. The first kicks you can feel from outside typically come around weeks 22–26. This kind of closeness means a lot
Discuss whether you want to know the sex at the upcoming scan, so you agree when the question comes
Help make the sleep environment comfortable. A pregnancy pillow can make a big difference to sleep quality
Offer massages for the lower back and shoulders — the changed posture causes a lot of tension
Start looking into childbirth preparation classes nearby. Many classes have waiting lists, so it is wise to book early

Tips for Week 16

Sleep on your side: Use a pregnancy pillow or regular pillow between your knees for better comfort. ACOG recommends side-lying from now on
Prepare for the anatomy scan: Talk about the sex question, and note questions for your midwife
Strengthen your back: Simple back exercises and Kegel exercises can prevent pain
Moisturise your skin: Use a good moisturiser or oil on your abdomen daily to keep skin soft
Adapt your exercise: Avoid exercises while lying on your back from now on, and switch to safe alternatives
Document your bump: Take weekly photos
Book a childbirth preparation class: Many classes fill up quickly — check what is available locally

When to Contact Your Doctor

Contact your doctor or midwife if you experience:

Pain only on one side of the abdomen that is persistent
Watery discharge that may indicate amniotic fluid leaking
Fever or chills
Persistent headache with visual disturbances
Vaginal bleeding
Severe dizziness that does not resolve
Sudden swelling in face, hands, or feet

Nutrition and Nutrients at Week 16

According to ACOG and WHO, several nutrients are especially important in the middle of the second trimester:

Iron

Iron needs increase significantly as blood volume rises. Good iron sources are lean red meat, beans, lentils, and fortified cereals. Take iron with vitamin C for better absorption. Avoid taking iron and calcium at the same time — they inhibit each other's absorption.

Calcium

Around 1,000 mg daily (per ACOG). Important for your baby's bone development. Good sources are dairy products, broccoli, kale, and almonds.

Omega-3 (DHA)

Crucial for brain development. ACOG and WHO recommend oily fish 2–3 times per week, or fish oil as a supplement.

Vitamin D

600 IU (15 micrograms) daily as a supplement, recommended by ACOG for all pregnant people. Essential for calcium absorption.

Fibre and Fluids

Constipation is common in pregnancy. Eat fibre-rich foods (whole grain products, vegetables, fruit) and drink at least 1.5–2 litres of fluid daily.

Foods to Avoid

Raw or undercooked meat and fish (risk of toxoplasmosis and listeria)
Soft cheeses and mould-ripened cheeses (risk of listeria)
Unpasteurised dairy products
High-mercury fish (shark, swordfish, king mackerel, tilefish)
Alcohol (no safe amount according to WHO)
More than 200 mg caffeine daily (about 2 cups of coffee)

Gestational Diabetes — What You Should Know

It can be useful to know about gestational diabetes, even though the test is usually done around weeks 24–28:

What Is Gestational Diabetes?

Gestational diabetes is high blood sugar that occurs during pregnancy. It affects about 3–5% of pregnant people and occurs because pregnancy hormones make the body less sensitive to insulin.

Risk Factors

BMI over 25 before pregnancy
Age over 25 years
Previous gestational diabetes
Diabetes in a close family member
Previously large baby (over 4.5 kg)

What You Can Do Now

Eat regularly and spread meals throughout the day
Choose whole grains over white bread and pasta
Be physically active — exercise improves insulin sensitivity
Limit sugary foods and drinks

The test for gestational diabetes (glucose tolerance test) is usually done around weeks 24–28. Talk to your midwife if you have risk factors and may need to be tested earlier.

Did You Know?

Your baby can grip the umbilical cord: The coordinated movements mean your baby can now grip and hold the umbilical cord. This is an important grasp reflex your baby will need after birth to hold on
Eyes are moving behind closed lids: Even though the eyelids are closed, the eyes can move slowly from side to side. The eyes will not open until around week 26, but the optic nerves are already developing
The placenta weighs almost as much as your baby: At week 16, the placenta weighs about 100–120 grams — almost as much as the baby. It grows throughout pregnancy and weighs about 500–600 grams at birth
Your baby has a sleep pattern: The fetus sleeps most of the day — up to 18–20 hours — with active periods in between. These periods can last 5–20 minutes, and it is often during active periods that you will eventually feel kicks
Relaxin makes your joints looser: Your body is producing the hormone relaxin, which makes ligaments softer and more elastic. This prepares the pelvis for birth but also makes you more prone to sprains and instability

Frequently Asked Questions About Week 16

When will I feel the first kicks?

First-time parents typically feel the first movements between weeks 18 and 22, while those who have been pregnant before often feel them earlier — around weeks 15–18. The first movements often feel like bubbling, butterflies, or a light tickling sensation. Placental position can also affect when you feel them — an anterior (front) placenta dampens the sensation and means you feel kicks later.

Should I stop sleeping on my back?

ACOG and the NHS recommend side-lying, preferably left side, from around weeks 16–20. As the uterus gets heavier, lying on your back can put pressure on the vena cava and reduce blood flow to your baby. Do not worry if you wake up on your back — your body usually gives you a signal (discomfort, dizziness) that makes you turn. Just turn back onto your side.

What are stretch marks, and can they be prevented?

Stretch marks (striae gravidarum) are small tears in the deeper layers of skin that occur when skin stretches rapidly. They are pink or purple at first and fade to silvery white after birth. Genetics plays the biggest role — if your mother got stretch marks, there is a higher chance you will too. Good moisturising and gradual weight gain can help a little. They are completely harmless and very common.

Is it normal to have more discharge now?

Yes, increased vaginal discharge is completely normal in pregnancy. It is caused by increased blood flow to the pelvic area and hormonal changes. Discharge should be light or white and odourless. Contact your doctor if it is greenish, yellowish, has an unpleasant smell, or causes itching — it may indicate infection.

What should I think about regarding exercise after week 16?

From week 16, ACOG recommends avoiding exercise while lying flat on your back. The growing uterus can press on the vena cava and reduce blood flow. Switch to standing, seated, or side-lying exercises. Swimming, walking, prenatal yoga, and Kegel exercises are still safe and recommended. Use adapted exercise programmes for pregnant people.

When should I book a childbirth preparation class?

It is wise to book classes now, as many fill up quickly. Most childbirth preparation classes are held at weeks 28–36. Check what is available at the hospital where you plan to give birth, or through local health services or private providers. Many also offer online classes. Start with a plan and keep track of important dates using our due date calculator.

Is it normal to have more vivid dreams during pregnancy?

Yes, many pregnant people experience more intense and vivid dreams, including dreams about their baby, the birth, and parenthood. This is caused by hormonal changes, more frequent night-time wakings (which makes you more likely to remember dreams), and subconscious processing of the major life change ahead. Nightmare-like dreams are also common and do not mean something is wrong. If your dreams are very distressing, talk to your midwife.

Can I continue exercising as before?

You can safely continue most forms of exercise you did before pregnancy, with some adjustments. From week 16, you should avoid exercises while lying on your back (per ACOG). Also avoid contact sports, activities with high fall risk, and scuba diving. Listen to your body, reduce intensity as needed, and make sure you can hold a conversation while exercising. Kegel exercises and adapted strength training are always safe options.

How do I know if my discharge is normal?

Normal vaginal discharge in pregnancy is light or white, odourless, and thin or slightly creamy. The amount increases through pregnancy and is completely normal. Contact your doctor if discharge is greenish, yellowish, has an unpleasant smell, causes itching (may indicate thrush), is very clumpy, or is watery and copious (may indicate amniotic fluid leaking). Watery discharge should always be checked quickly by your midwife or doctor.

Should I take prenatal vitamins?

ACOG recommends that all pregnant people take a vitamin D supplement (600 IU / 15 micrograms daily). Many choose to take a prenatal vitamin supplement containing vitamin D, iron, folic acid, and iodine in one tablet. Talk to your midwife about what is right for you based on your diet and blood test results.

Is it normal to have back pain at week 16?

Yes, back pain is very common from the second trimester. The growing bump changes your centre of gravity, and the hormone relaxin makes joints looser. Tips for relief: good posture, regular exercise, Kegel exercises, swimming, and shoes with good support. Avoid standing for long periods, and talk to your midwife about physiotherapy if pain is affecting daily life. Many areas offer free physiotherapy for pregnant people.

Can constipation affect my baby?

No, constipation is uncomfortable for you but harmless for your baby. It is very common in pregnancy and is caused by the hormone progesterone slowing the bowel, and by any iron supplements you may be taking. Eat fibre-rich food (whole grains, vegetables, fruit, prunes), drink enough water (1.5–2 litres daily), and be physically active. Prunes and prune juice are natural and safe remedies. Talk to your midwife about gentle laxatives if needed.

Follow your whole pregnancy week by week with the pregnancy timeline, and use our due date calculator to keep track of important dates.

Next week: Your baby is growing rapidly, and brown fat is beginning to form to keep your baby warm!