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

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.

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.

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.

Your week 28 checklist

This week:

• Attend your 28-week midwife appointment.
• Receive your anti-D injection if you are 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.