In pregnancy, multiple parts of your body cooperate to support you and your baby. You feel this most acutely in your third trimester. Baby is bigger than ever, and you’ll soon give birth. If you’re at this stage, you might feel more tired and uncomfortable, but congratulations! You’re nearly there now. Let’s look at what’s happening to your body, what you can manage, and when to call the doctor.

How will my body change in the third trimester?

You’ll feel your most voluptuous in this trimester, as while pregnancy weight gain varies, the bulk of it happens from the mid-second trimester onwards.

You might notice your face, hands, legs, and feet feel more swollen. This isn’t just weight gain; pregnant women produce a lot more of the hormones aldosterone and cortisol, which cause fluid retention. It’s normal for cortisol to quadruple and aldosterone to increase by as much as tenfold. Fluid also accumulates because your growing bump disrupts the blood flow from your legs to your heart. This makes fluid back up in your leg veins and seep out into the surrounding tissues. You can’t always make the swelling go away, but elevating your legs can help, as can reducing your salt intake, walking, and avoiding standing for extended periods. Speak to your doctor about swelling that suddenly increases in any part of the body, especially if it’s swelling in just one leg or calf.

Hormonal increases can cause mood swings, and their impact is physiologically huge. This is because you are making so much more of them. For example, a woman’s oestrogen production, which peaks in the third trimester, is greater in a single pregnancy than over the course of her entire nonpregnant life.

Oestrogen and progesterone are the two main hormones produced by the ovaries and placenta during pregnancy, and they peak in this trimester. It makes your uterus and breasts grow and prepares your breasts for feeding. Stretch marks on your breasts or tummy are common by the third trimester because of this growth, your genes, and increased cortisol, making your skin less elastic. Stretch marks are nothing to worry about, but if they itch, you should moisturise, as frequent scratching can damage your skin.

If you are itching without a rash or mark anywhere on your body, particularly on your hands or feet, let your doctor or midwife know. This is a common symptom of a condition called obstetric cholestasis of pregnancy that can cause serious complications they’ll want to address as soon as possible. We’re not really sure of the cause of cholestasis, but it is something to flag as soon as you notice it. Other less common symptoms include yellowing of your eyes and skin and nausea or loss of appetite.

Pregnancy hormones can also make your ligaments softer and stretchier. This helps your body prepare for labour and can put pressure on your pelvis and lower back weeks before you're there. You can take paracetamol to ease any back pain, unless your GP or midwife advises otherwise.

Progesterone levels also increase in the third trimester. During pregnancy, it relaxes your bowels to help prevent constipation. It also relaxes your blood vessels. The vessels in your nose are very delicate, and nasal bleeding and congestion are very common in your third trimester. This is nothing to worry about unless you experience profuse bleeding. Progesterone helps prepare your body for labour by strengthening your pelvic floor, which you can support with daily exercises.

Relaxin is another reproductive hormone produced by your ovaries and the placenta. It helps prepare the body for labour and delivery by loosening the muscles, ligaments, and joints of the pelvis. During the final days of pregnancy, relaxin helps the cervix soften in anticipation of childbirth. Your uterine cells will also produce prostaglandins for this reason.

Prolactin is a hormone that promotes lactation after birth, though its steady increase during pregnancy may make your nipples leak a vitamin-rich substance called colostrum. This is most common in the final weeks and can happen at odd times, such as when you hear a baby crying. It’s nothing to worry about, and you may like to talk to your healthcare team about expressing and storing it from Week 36, as some mothers, such as those who are planning an induction, find this useful.

Oxytocin production is usually increasing throughout your pregnancy. This “love hormone” stimulates your uterus to have contractions during labour. Some of you may have heard the expression “what gets the baby in gets the baby out,” because it’s also released during orgasm.

How does my womb change during my third trimester?

It gets bigger! Your uterus grows from week six of your pregnancy. This growth will peak early in this third trimester, at about 28 weeks, and from then on, growth slows, but the tissue continues to stretch to accommodate your baby—the uterus is a very muscular organ!

As you approach your delivery date, you may feel your abdomen tighten for about 30 seconds several times a day or see it harden and remain tense for several seconds. This is your uterus having Braxton-Hicks contractions. They can happen at any time during your pregnancy but are most common in the third trimester. We don’t really know why women get Braxton-Hicks contractions, and some women don’t actually feel them, so don’t worry if you haven’t.

Even if you’re taking things slowly, as is recommended, your growing bump pushes up against your lungs as your third trimester begins, and with your extra weight, you may feel more breathless than usual. As your baby settles into the head-down cephalic position and moves lower in your pelvis towards the end of your pregnancy, this breathing problem should ease. Breathlessness can also be a sign of anaemia or something even more serious, so you should certainly mention this symptom to your doctor, especially if you're having significant difficulty breathing at rest and/or if breathlessness is accompanied by a tightening in your chest or upper back.

Your larger uterus also puts pressure on your stomach and intestines, which, combined with your pregnancy progesterone, can cause indigestion and heartburn. Antacids are safe during the third trimester. It’s normal to feel bloated, and your digestive system is generally slower. Drinking lots of water and eating things like dried apricots can help.

As your mum may warn you, the weight and pressure of your uterus decrease blood flow from your lower body and can cause varicose veins. These are far more influenced by genes than the amount of weight you’ve gained, so you can’t really prevent them, but you can keep them from getting worse by taking the same steps as you would to manage fluid retention. They should improve after birth and can be cleared through minor surgery later if they bother you. Varicose veins can also appear on your rectum in the form of haemorrhoids, another delightful third trimester symptom. Over-the-counter creams are safe while pregnant or breastfeeding.

How do my cervix and pelvis change in the third trimester?

As we’ve seen, hormones relax your pelvis. The pelvis is a bony tunnel your baby will go through. The cervix, with a canal inside it, connects the base of your uterus to your vagina. It remains long and closed until late in the third trimester, when your baby turns into a head-down position and starts to drop down into the pelvis. This is called the engagement of the baby’s head. It puts pressure on the cervix, causing it to efface (thin out) and dilate in preparation for labour.

If you're a first-time mum, your baby may start to engage at 36 weeks. If you've given birth before, your baby may not engage until just hours before labour.

A clump of mucus forms in the cervical canal in early pregnancy to protect your uterus and baby from infection. You lose it as your cervix thins, and it leaves your body through the vagina. Some women lose this mucus plug gradually over the late third trimester, others all at once and much closer to labour. It looks like extra discharge and can be clear, yellowish-white, beige, pink, or tinged with red or brown streaks of blood. This can be normal but is a reason to check in with your doctor or midwife, particularly if you are fewer than 37 weeks pregnant.

What are some other signs I should call the doctor about?

The following are red flags that should be reported to a professional as soon as possible:

Headaches, dizziness, or vision problems
Mental health concerns, such as severe anxiety or a desire to self-harm
Severe nausea and/or vomiting
Heavy vaginal bleeding
Thrush
Extreme fatigue
Strong and/or persistent stomach pain
A temperature over 37.5 degrees Celsius (even if you have no other flu or cold symptoms)
You can’t feel your baby moving, or it feels like they’re moving less than usual or very slowly.
Regular contractions every 2-3 minutes, lasting over 40 seconds for up to 2 hours, warrant immediate medical attention.

There’s also no reason not to call if you simply feel something is wrong. You’re never bothering anyone, and your maternal instincts are priceless.