Week 33: The Immune System Gets a Boost

Your baby is getting a real immunity boost! Through the placenta, your body is transferring antibodies (immunoglobulins) that protect baby against diseases in the first months after birth. Meanwhile, your little one is continuing to grow stronger day by day.

With just seven weeks until your due date, it's important to have preparations underway. Your hospital bag should be packed soon, and it's a good idea to familiarize yourself with signs of labor, GBS testing, and what happens in the final weeks of pregnancy. Prenatal appointments are becoming more frequent now, and your midwife is closely monitoring both you and baby.

Baby's Development

Antibodies: Baby is receiving immunoglobulins (IgG) from you through the placenta, providing protection against infections after birth
Amniotic fluid: Baby is now drinking about 500 ml of amniotic fluid daily and urinating it back out — good practice for the kidneys and digestive system
Skull: The skull bones are soft and flexible, with fontanelles (soft spots) that make it easier to pass through the birth canal
Pupils: Baby's eyes respond to light, and pupils can dilate and constrict
Weight and length: Baby weighs around 1.9–2.1 kg and measures about 44 cm
Fat storage: The fat layer under the skin is increasing and gives baby a rounder appearance — important for temperature regulation after birth
Lungs: Surfactant production continues. Lungs are maturing rapidly but still need a few more weeks
Brain development: The brain is growing intensely and forming new neural connections at a rapid pace

The Immune System in Detail

The transfer of antibodies from mother to baby through the placenta is a fascinating process. Your IgG antibodies — which you've built up throughout life through illness and vaccinations — cross the placenta and give baby temporary protection. This passive immunity lasts approximately 3–6 months after birth, and is why newborns have some resistance to many common infections.

This is also why health authorities including the CDC and WHO recommend that pregnant women get flu and whooping cough (pertussis) vaccines. The antibodies you produce are transferred to baby and provide protection in the first months of life, before baby's own vaccination schedule begins.

Your Body

Sleep difficulties: The growing belly makes it hard to find a comfortable sleeping position — try a support pillow between your knees
Braxton Hicks: Practice contractions become more frequent and noticeable, but they are irregular and harmless
Gait change: You may notice you're waddling a little more — that's your pelvis adjusting to the extra weight
Heartburn: The uterus pushes the stomach upward, and many experience more heartburn now. Eat smaller portions and avoid lying down right after meals
Swelling: Feet and ankles may swell more, especially in the afternoon. Elevate your legs when resting
Constipation: Hormones slow bowel function. Eat fiber-rich foods, drink plenty of water, and keep moving
Pelvic pressure: You may feel increasing downward pressure as baby grows

Heartburn and Digestive Issues

Heartburn is one of the most common complaints in the third trimester. It happens because the uterus pushes the stomach upward, while the hormone progesterone relaxes the muscle between the esophagus and stomach.

Tips for heartburn:

Eat several small meals instead of a few large ones
Avoid spicy, fatty, and acidic foods
Don't lie down right after a meal — wait at least 2–3 hours
Slightly elevate the head end of your bed
Drink milk or take an antacid (ask your pharmacist about safe options in pregnancy)
Eating slowly and chewing thoroughly can also help

Good to Know

The immunity baby receives from you now is especially important. These antibodies protect the newborn in the first 3–6 months, before baby's own immune system is strong enough. This is why it's wise to stay healthy and eat a varied diet during this period.

Make sure you're getting enough iron. Baby is building up its own iron stores now, and that can leave you feeling extra tired. Good sources of iron include red meat, beans, lentils, and leafy green vegetables. Combine with vitamin C (citrus, bell pepper) for better absorption, and avoid taking iron at the same time as dairy products or coffee, which inhibit absorption.

Remember to drink enough water — at least 2 liters daily. It helps with constipation and keeps amniotic fluid levels up.

Many people also experience poorer sleep quality now. Sleep on your left side with a pillow between your knees for the best comfort and blood flow to baby.

Many people experience more heartburn and constipation at this stage. Eat several small meals throughout the day instead of three large ones, and choose fiber-rich foods like whole grains, fruit, and vegetables. Keep moving with short walks — it helps with both constipation and back pain.

GBS Testing and Preparations

Group B Streptococcus (GBS)

GBS testing policies vary by country. In some places, all pregnant women are routinely swabbed at around 35–37 weeks; in others, testing is risk-based. Ask your midwife or doctor whether GBS testing is recommended for you.

Risk factors for GBS-related complications include:

Preterm labor (before week 37)
Waters breaking more than 18 hours before delivery
Fever during labor
A previous baby with GBS infection
GBS found in urine earlier in this pregnancy

About 20–30% of women carry GBS without knowing it. The bacteria is harmless to you, but can in rare cases cause infection in newborns. If GBS is confirmed, IV antibiotics are given during labor.

Hospital Bag

Now is a good time to pack your hospital bag. Births can come earlier than planned, and it's reassuring to have everything ready.

Hospital Bag — Packing List

Here are the essentials:

For You

ID and health/insurance documents
Comfortable nightgown or pajamas and a robe
Slippers and socks (floors can be cold)
Nursing bra and nursing pads
Postpartum pads (large, soft)
Toiletries, lip balm, and hair ties
Phone charger
Snacks and drinks
Your birth plan

For Baby

Onesies and sleepsuit in newborn size
Hat and socks
Newborn diapers/nappies
Soft muslin or blanket
Car seat for the ride home (must be in the car)

For Your Partner

Snacks and drinks
Phone charger
Change of clothes
Camera
Something to read or do between contractions

Preparing for the Postnatal Period

With seven weeks left, it's smart to plan for the weeks after birth:

Practical Preparation

Freezer meals: Cook extra portions of your favorite dinners and freeze them. 10–15 portions give a good buffer
Shopping: Keep a list of the most essential items for the first weeks
Baby clothes: Wash and sort clothes in newborn and 0–3 month sizes
Baby's room: Check that everything is in place — cot, changing area, diapers, clothes

Your Support Network

Talk with family and friends about who can help in the first weeks
Find out what postnatal support is available from your local health services
Look into local breastfeeding groups
Read up on breastfeeding in advance so you feel a little more prepared

Exercise in Week 33

Moderate exercise is still recommended, even though your body feels heavier. Regular movement helps with many complaints.

Good Activities Now

Swimming: Takes full weight off your body and relieves back pain. Many pregnant women find it the most comfortable form of exercise at this stage
Short walks: 15–20 minutes daily keeps your body moving and helps with constipation
Prenatal yoga: Breathing exercises and hip-opening postures prepare you for birth
Pelvic floor exercises: Especially important now. Strong pelvic floor muscles help during birth and speed up recovery
Birth ball exercises: Sitting on an exercise ball can relieve pelvic pressure

Nutrition in Week 33

Baby is building up iron stores and continuing to grow rapidly. Good nutrition is especially important now.

Iron — Especially Important

Iron needs increase significantly in the third trimester. Tips for getting enough:

Eat red meat 2–3 times per week
Combine plant-based iron sources (beans, lentils, spinach) with vitamin C for better absorption
Avoid taking iron at the same time as coffee, tea, or dairy products — they inhibit absorption
Your midwife checks iron levels at appointments

Other Important Nutrients

Calcium: For baby's bone development. Dairy products, leafy green vegetables
Omega-3 (DHA): For brain development. Fish 2–3 times per week
Fiber: Against constipation. Whole grains, fruit, vegetables
Water: At least 2 liters daily

Birth Anxiety

It's normal to feel nervous or anxious about birth. Birth anxiety is common and there is help available.

What Can Help?

Talk about your concerns with someone you trust
Antenatal classes provide knowledge and confidence
Write a birth plan with your wishes
Practice breathing techniques and relaxation
Visit your birth center or hospital ward beforehand if possible

Speak with your midwife if anxiety is affecting your daily life. Many hospitals offer appointments for pregnant people with birth anxiety.

For Your Partner

Help create a comfortable sleeping space with extra pillows — sleep deprivation is real now
Offer to massage feet and ankles in the evening — it eases swelling and is good care
Read about signs of labor together so you both know what to look for as it gets closer
Pack your own bag for the hospital — snacks, charger, change of clothes, camera
Check parental leave entitlements and any application deadlines

Tips for Week 33

Hospital bag: If you haven't packed it yet, now is the time — births can come earlier than planned
Fetal movements: Get to know your baby's usual movement pattern — contact your midwife if you notice a clear change
Relaxation: Try a few minutes of deep breathing or meditation before bed for better sleep
Pelvic floor exercises: Continue daily — they prepare your body for birth and help with recovery afterward
Freezer meals: Start cooking extra portions and freezing them for the postnatal period
Birth plan: Finish writing your birth plan with your wishes for labor and birth
Iron-rich food: Focus on foods high in iron — red meat, lentils, beans, and spinach combined with vitamin C

When to Contact a Doctor

Contact your doctor or midwife if you experience:

Regular contractions (more than 4 per hour) that don't ease with rest
Fluid leaking from the vagina (could be amniotic fluid)
Significantly reduced fetal movements
Sudden swelling in the face or hands, combined with headache or visual disturbances
Severe abdominal pain that doesn't ease
Fever above 38°C (100.4°F)
Vaginal bleeding

Always call if you're worried. It's better to ring one extra time than not at all. Your maternity unit always has a midwife available who can guide you.

Did You Know...?

Your baby is now drinking about 500 ml of amniotic fluid daily and urinating it back out. This is important training for the kidneys and digestive system, and also helps regulate the amount of amniotic fluid
Baby's skull is naturally soft and flexible. The skull bones are not fused but overlap during birth to make it easier to pass through the birth canal. This is completely harmless and normalizes after birth
The antibodies baby receives from you now through the placenta provide protection against many of the diseases you've had or been vaccinated against. This "passive immunity" lasts 3–6 months after birth
The fontanelles (soft spots) on baby's head don't close fully until during the first or second year of life. They allow the brain to grow rapidly after birth
Most childhood vaccination programs begin at around 2–3 months of age. Until then, baby depends on the antibodies received from you through the placenta

Common Questions About Week 33

Is it normal to be waddling now?

Yes, completely normal. The hormone relaxin loosens the pelvic joints in preparation for birth, and the extra weight at the front shifts your center of gravity. This naturally makes many pregnant people adjust their gait — it's your body's smart way of maintaining balance.

Should I worry about iron deficiency?

Iron needs increase significantly in the third trimester because baby is building up its own iron stores. Many pregnant people need an iron supplement during this period. Symptoms of iron deficiency can include extra fatigue, dizziness, and paleness. Your midwife checks your iron levels at appointments and can recommend a supplement if needed.

How often should I feel fetal movements?

Baby now has clear sleep and wake cycles, so you'll notice periods of much activity and periods of quiet. The most important thing is that you recognize your baby's usual pattern and respond if it changes noticeably. Contact your midwife if you're unsure.

What is GBS, and will I be tested?

GBS (Group B Streptococcus) is a bacteria that about 20–30% of women carry without symptoms. Testing policies vary by country. The test is a simple swab. If the result is positive, IV antibiotics are given during labor to protect baby.

How do I know if it's real contractions or Braxton Hicks?

Braxton Hicks are irregular, vary in intensity, and go away with rest or position changes. Real contractions come at regular intervals, get stronger, and don't stop no matter what you do. Contact your maternity unit if you're unsure, and use a contraction timer app to track the intervals.

Should I get the flu vaccine during pregnancy?

Yes — the CDC, WHO, and NHS all recommend the flu vaccine for all pregnant women during flu season. The vaccine is safe in pregnancy and provides protection for both you and baby. The antibodies are transferred to baby through the placenta and protect them in the first months of life.

What do I do about constipation?

Constipation is very common in the third trimester and is caused by hormones slowing bowel function. You can help digestion by eating fiber-rich foods (whole grains, fruit, vegetables), drinking at least 2 liters of water daily, and staying active. Prunes can also help. Ask your pharmacist or midwife about gentle laxatives if dietary changes aren't enough.

When should my hospital bag be ready?

Your hospital bag should ideally be packed and ready from around week 35–36, but it's a good idea to start now. Births can come earlier than planned.

How do I manage swollen legs?

Swelling in the legs and feet is common in the third trimester and is caused by increased fluid volume and pressure from the uterus. Elevate your legs when resting, wear compression socks, drink enough water, and avoid standing still for long periods. Sudden severe swelling, especially in the face and hands, should be checked by a doctor as it can indicate preeclampsia.

How do I prepare for breastfeeding?

It helps to read about breastfeeding before birth. According to the WHO and AAP, exclusive breastfeeding is recommended for the first 6 months. Prepare by getting a nursing bra and nursing pads, reading about feeding positions, and asking about breastfeeding classes at your hospital or birth center. In the first days, your breasts produce colostrum (first milk), which is incredibly nutritious and full of antibodies. Full milk production usually comes in 2–4 days after birth.

What is the placenta and what happens to it after birth?

The placenta (afterbirth) is the organ that has supplied baby with oxygen and nutrition throughout pregnancy. It is attached to the uterine wall and connected to baby via the umbilical cord. After birth, the placenta detaches and is delivered in the third stage of labor, usually 15–30 minutes after baby. The midwife examines it to make sure it's complete. The placenta weighs approximately 500–600 grams at term.

Next week: The lungs are maturing and baby is getting a thicker protective layer of vernix.