Pregnancy Week 28: Anti-D, Iron Levels, and Your Baby's Sleep Cycles

8 min read

Quick answer: At 28 weeks you'll usually see your midwife for anti-D injections if you're rhesus negative, and a blood test to check for anaemia. Your baby measures around 37.6cm crown to heel and weighs about 1 kilogram, gaining roughly 200g a week. Baby has established sleep cycles with REM sleep, and is laying down fat under the skin.

What parents need to know

Week 28 is an important one for antenatal care. You'll likely have an appointment with your midwife this week, during which you'll receive anti-D injections if you're rhesus negative and be tested for anaemia. Meanwhile, your baby is continuing to develop rapidly in preparation for life outside the womb.

Length	About 37.6cm crown to heel
Weight	Around 1 kilogram
Weekly weight gain	Approximately 200g per week
This week's appointment	28-week midwife appointment
Tests offered	Anti-D if Rh-, plus anaemia blood test

How big is your baby at 28 weeks?

Your baby now measures approximately 37.6cm from crown to heel and weighs around 1 kilogram, a significant milestone. They've now crossed the 1kg mark and will continue gaining approximately 200g per week for the next several weeks.

What's happening with your baby?

One of the most fascinating developments this week is that your baby has established sleep cycles with periods of REM (rapid eye movement) sleep — the same stage of sleep associated with dreaming in adults and children. Whether babies dream in the womb is unknown, but the presence of REM sleep indicates significant neurological development. Your baby is also accumulating fat beneath the skin, giving them a more rounded appearance. Their skin, previously translucent, is becoming less see-through. The bone marrow has taken over from the liver as the primary site of red blood cell production, which is an important step in the baby's developing circulatory system.

Anti-D and rhesus status

At your 28-week appointment, you'll be offered anti-D injections if your blood group is rhesus negative (Rh-). The rhesus factor is a protein on the surface of red blood cells. If you are Rh- and your baby is Rh+, there is a risk that your immune system could produce antibodies against your baby's blood cells, which could affect this pregnancy (if blood mixing occurs) or future pregnancies. Anti-D injections prevent this from happening. You'll also receive anti-D after delivery if your baby is found to be Rh+.

Checking for anaemia

A blood test at 28 weeks checks your haemoglobin levels to screen for anaemia. Anaemia is common in pregnancy because the body needs significantly more iron to support the increased blood volume and the baby's developing red blood cells. Symptoms include fatigue, breathlessness, and looking pale. If your iron levels are low, your midwife will advise on iron supplementation and dietary sources of iron. Foods rich in iron include red meat, pulses (lentils, beans, chickpeas), tofu, dark leafy greens, and fortified cereals. Consuming vitamin C alongside iron-rich foods helps absorption. Do not take cod liver oil or supplements containing vitamin A (sometimes called retinol), and avoid liver and liver products, because too much vitamin A can harm your baby's development. Always check the label.

What's happening in your body?

You may be noticing more discomfort in the pelvic area this week. Pelvic girdle pain (PGP), sometimes called symphysis pubis dysfunction (SPD), is a common condition in pregnancy where the joints of the pelvis become less stable due to the hormone relaxin. It can range from mild discomfort to significant pain. If you're experiencing pelvic pain, speak to your midwife, who can refer you to a physiotherapist. There are also practical strategies that can help, such as keeping your knees together when getting in and out of the car, avoiding asymmetrical postures, and using a pillow between your knees at night.

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
your waters break, even if labour has not started
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'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

Go to sleep on your side. From 28 weeks, the safest position to go to sleep is on your side, either left or right. Research suggests that, after 28 weeks, falling asleep on your back can double the risk of stillbirth. This includes daytime naps. If you wake up on your back, just turn onto your side and go back to sleep.

Your week 28 checklist

This week:

Attend your 28-week midwife appointment.
Receive your anti-D injection if you're Rh-.
Ask about your iron levels and address any anaemia.
Mention any pelvic pain to your midwife.
Continue monitoring your baby's movements.

Frequently asked questions

Why am I offered anti-D at 28 weeks?

Anti-D is offered if your blood group is rhesus negative. If you are Rh- and your baby is Rh+, your immune system could produce antibodies against your baby's blood cells, affecting this or future pregnancies. Anti-D injections prevent this.

What does the 28-week blood test check for?

It checks your haemoglobin levels to screen for anaemia, which is common in pregnancy because your body needs more iron for the increased blood volume and your baby's developing red blood cells.

Which foods help with low iron in pregnancy?

Iron-rich foods include red meat, pulses such as lentils, beans and chickpeas, tofu, dark leafy greens and fortified cereals. Eating vitamin C alongside them helps absorption. Your midwife will advise on supplementation if your levels are low.

What can I do about pelvic pain at 28 weeks?

Speak to your midwife, who can refer you to a physiotherapist. Practical strategies help too: keeping your knees together getting in and out of the car, avoiding asymmetrical postures, and using a pillow between your knees at night.

Sources & further reading

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