You are 30 weeks and 6 days

Once your baby is making red blood cells in earnest, in theory your immune system could begin to harm him.

64 days until your due date

At 30 weeks, your baby's red blood cell production moves from the liver to the bone marrow. These cells are unlikely to be the same blood group as yours, and small numbers often leak across the placenta, where your body sees them as foreign and attacks them.

ABO blood group doesn't matter, because although antibodies to groups A, B, AB, or O attack your baby's cells in your blood, they're too large to cross the placenta. But everyone is also Rhesus positive (85 percent) or negative (15 percent). If you're Rh-negative and your partner Rh-positive, your baby may be Rh-positive. Rh-negative women make antibodies to Rh-positive cells, and these are small enough to cross the placenta, where they can attack the baby's blood cells in large numbers, causing anemia. First pregnancies are rarely affected.

So around now you'll be given an injection of Rh immunoglobulin (RhIg), with another after the birth. It's too large to cross the placenta and mops up any of your baby's blood cells in your circulation, preventing your immune system from attacking your baby.

Focus on

Your health: A good night's sleep

Insomnia is common in pregnancy and can cause tiredness, stress, anxiety, and irritability, whether it's caused by your size, back pain, heartburn, getting up to urinate, or something else. A warm bath or small snack before bed may help, as can relaxation techniques such as deep breathing, or a calming scent on your pillow. Exercise during the day. If you still can't sleep, get up and do something relaxing, such as reading, watching TV, or listening to calm music, until you feel sleepy, and make up for lost sleep with daytime naps.

Good to know

Amniotic fluid

Your baby passes and reabsorbs about 16 fl oz (0.5 liter) of urine a day, and the amniotic fluid peaks at 1.75 pints (1 liter) at 35 weeks. After that it starts to fall and can be as little as 3.5–7 fl oz (100–200 ml) in an overdue pregnancy.

Low fluid (oligohydramnios) can be a sign of a growth-restricted baby or one with kidney problems. Too much fluid (polyhydramnios) may occur with twins or triplets and is also linked to physical abnormalities in the baby or diabetes in the mother. After 40 weeks, fluid levels need checking regularly to make sure they aren't falling too steeply, and if an overdue baby is thought to be at risk, induction will be recommended.

This is general information based on NHS guidance, not medical advice, and every pregnancy is different. Talk to your midwife or GP about anything that worries you. If your baby's movements slow down or change, or you have bleeding, severe pain or leaking fluid, call your maternity unit straight away. In an emergency, call 999.

Your health: A good night's sleep

Amniotic fluid

Appointments and key dates around now