Pregnancy Week 27: Welcome to the Third Trimester

8 min read

Quick answer: Week 27 begins the third trimester. Your baby measures about 36.6cm from crown to heel and weighs around 875 grams, with the brain forming its folds and grooves and hearing well developed. From 28 weeks antenatal appointments become more frequent, and anti-D is offered if you are rhesus negative. If movements reduce or feel different, contact your midwife or maternity unit immediately.

What parents need to know

Congratulations, you've reached the third trimester. Week 27 marks the beginning of the final stretch of pregnancy, and your baby is growing and developing quickly. The third trimester brings new considerations, and your antenatal appointments will become more frequent from here on.

The Crib

Your baby at 27 weeks

The third trimester begins, and antenatal appointments become more frequent from here on

Weight: around 875 grams

Roughly the weight of a head of cauliflower

Trimester: third trimester begins

Appointments (first baby): 28, 31, 34, 36, 38, 40 and 41 weeks

At 28 weeks: anti-D if rhesus negative, plus anaemia blood test

Sources: NHS, Tommy's, NCT. General information, not medical advice.

How big is your baby at 27 weeks?

Your baby now measures approximately 36.6cm from crown to heel and weighs around 875 grams, roughly the weight of a head of cauliflower. They're beginning to look more like a newborn, though they're still slim and will triple in weight before birth.

What's happening with your baby?

Your baby's brain continues to develop at a remarkable rate this week, and the surface of the brain — which was smooth earlier in pregnancy — is now forming its characteristic folds and grooves (gyri and sulci). These folds dramatically increase the surface area of the brain, allowing for the complex neural connections that support thought, memory, movement, and sensation. Your baby's eyelashes are now growing, and they can blink their eyes open and shut. Their hearing is well developed and they can recognise the sound of your voice, your heartbeat, and other familiar sounds from the outside world.

Close-up of a baby's feet cradled in protective adult hands, symbolizing care.

What's happening in your body?

The third trimester brings new challenges as your growing bump puts increasing pressure on your body. Heartburn and indigestion are common as the growing uterus pushes against the stomach. Eating smaller, more frequent meals and avoiding lying down immediately after eating can help. Sleeping may become more difficult, and many women find a pregnancy pillow helpful for supporting the bump and reducing pressure on the hips and back.

Shortness of breath can occur as the uterus rises in the abdomen and puts pressure on the diaphragm. This typically improves somewhat as your baby 'drops' lower into your pelvis in the final weeks. Breathlessness that comes on suddenly, being out of breath when you're lying down, or breathlessness with dizziness needs to be checked straight away: call your midwife or maternity unit, or NHS 111. Call 999 or go to A&E if you have severe difficulty breathing, pain in your chest or upper back, a very fast heartbeat, or you pass out.

Your antenatal care in the third trimester

From week 28, your antenatal appointments will become more frequent. NHS guidelines recommend appointments at 28, 31, 34, 36, 38, 40, and 41 weeks (if you haven't delivered by then) for first-time mothers, and at 28, 34, 36, 38, and 40 weeks for women who have previously given birth. At these appointments, your midwife will check your blood pressure, test your urine, measure your fundal height, check your baby's position and heartbeat, and discuss any concerns.

At 28 weeks, you'll be offered anti-D injections if you are rhesus negative. This is important to protect any future pregnancies. You'll also be offered a blood test to check for anaemia.

Fetal movements in the third trimester

As you enter the third trimester, it's more important than ever to be aware of your baby's movements. By now, you should have a good sense of your baby's usual pattern of activity. According to Tommy's and NHS guidance, there is no specific number of movements you should be feeling each day — what matters is that you are familiar with what is normal for your baby and notice any change. If your baby's movements reduce or feel different, contact your midwife or maternity unit immediately — do not wait until the next day. Never use a home Doppler to check your baby's heartbeat as a substitute for seeking medical advice.

When to get help

Some symptoms in pregnancy can be a sign of something serious and need checking quickly. This is who to contact, and how soon.

Call 999 if:

you're bleeding from your vagina and the bleeding is heavy (soaking a period pad soon after putting it on), or you also have severe pain in your tummy, pain in your shoulder, or feel sick, faint, dizzy or lose consciousness
you think your baby is coming now and you have a strong urge to push (ask for an ambulance)
you have severe difficulty breathing (you're gasping, choking or not able to get words out) or your chest feels tight or heavy
you have pain and swelling in one leg and you also feel short of breath or have chest pain. A blood clot in the leg can travel to your lungs, which can be life-threatening
you have possible signs of sepsis, such as breathing very fast, being confused or having slurred speech, blue, pale or blotchy skin, a rash that does not fade when you press it, or a very high or very low temperature. Being pregnant makes sepsis more likely
you do not feel you can keep yourself safe (a mental health emergency is as serious as a physical one)

Always call 999 if you think it's a life-threatening emergency, no matter what stage of pregnancy you are.

Call your midwife or maternity unit now if:

your baby is moving less than usual, you cannot feel your baby moving anymore, or there is a change to your baby's usual pattern of movements
you have light bleeding or spotting, even if you have no pain or only mild tummy pain
you have stomach pain that is severe or does not go away after you've rested for 30 to 60 minutes, or stomach pain with regular cramping or tightenings, lower back pain, or pain when you pee
you're less than 37 weeks pregnant and you have a gush or trickle of fluid from your vagina (this could be your waters breaking), regular contractions or tightenings, period-type pains, or backache that's not usual for you
you have signs of pre-eclampsia: a severe headache that does not go away with simple painkillers, vision problems (such as blurred vision or seeing flashing lights), pain below the ribs, sudden swelling of the face, hands or feet, feeling very unwell, heartburn that does not go away with heartburn medicines, or being sick (vomiting)
your skin is very itchy (for example, it keeps you awake at night), the palms of your hands or soles of your feet are itchy, or the itching is worse at night. This can be a sign of a liver condition called intrahepatic cholestasis of pregnancy (ICP) that needs urgent treatment
your breathlessness comes on suddenly, you're out of breath when you're lying down, or you're breathless and also have chest pain or feel dizzy
you have pain or swelling in one leg, usually in the calf or thigh. This could be a blood clot (deep vein thrombosis, or DVT), which is more likely when you're pregnant
you have a high temperature (38C or above), or you feel hotter than usual or shivery. A high temperature can be a sign of an infection, so it's important to get it checked

If your baby's movements change, do not wait until the next day: call immediately, even if it's the middle of the night. Do not use a home doppler to check the heartbeat yourself. Even if you hear a heartbeat, this does not mean your baby is well.

If you cannot reach them, or you're not sure what to do, call NHS 111.

Speak to your midwife or GP if:

you have not felt your baby move by 24 weeks. Most people start to feel movements between 16 and 24 weeks. If this is your first baby, you might not feel them until after 20 weeks
you're worried about your mental health, or stress, anxiety or low mood are affecting your day-to-day life. If you need urgent help for your mental health, call 111 and select the mental health option, or ask for an urgent GP appointment

Your week 27 checklist

This week:

Celebrate reaching the third trimester.
Familiarise yourself with your baby's movement pattern.
Ensure you know how to contact your maternity unit if you are concerned about movements.
Make note of your upcoming antenatal appointments.
Start thinking about your hospital bag.

Sources & further reading

General information, not individual medical advice. Speak to your GP, midwife or health visitor about your baby’s needs.