At 30 weeks your baby's red blood cell production switches from the liver to the bone marrow. These red blood cells are unlikely to be of the same blood group as your own. Small numbers of these red blood cells often leak across the placenta; your body recognizes them as foreign and attacks them.
Your blood group is not important because, although antibodies to blood groups A, B, AB, or O attack your baby's cells in your circulation, they are too large to cross the placenta and attack your baby. Therefore differences in ABO blood groups do not matter. However, everyone is also Rhesus positive (85 percent) or negative (15 percent). If you are Rhesus negative (see Blood group) and your partner is Rhesus positive, your baby may also be Rhesus positive.
Rhesus negative women produce antibodies to rhesus positive blood cells; these are smaller than ABO antibodies and can cross the placenta. Once they do, large numbers of antibodies can attack your baby's blood cells, leading to anemia. First pregnancies are rarely affected. In pregnancy you are given an injection of the rhesus antibody "Rh immunoglobulin (RhIg)" around now-with another after the birth. The Rh immunoglobulin (RhIg) is in a form that it is too large to cross the placenta. This mops up any of your baby's blood cells in your circulation, preventing your immune system from attacking your baby.
Your baby excretes and reabsorbs about 16 fl oz (0.5 liter) of urine daily, and the amniotic fluid reaches a peak volume of 1.75 pints (1 liter) at 35 weeks. After this time the volume starts to decline and can be as little as 3.5-7 fl oz (100-200 ml) in an overdue pregnancy (see Overdue Baby).
Low levels of amniotic fluid, known as oligohydramnios , can be a sign of a growth-restricted baby or a baby with kidney problems. Excessive amniotic fluid, known as polyhydramnios , may be seen in twin or triplet pregnancies, and is also associated with physical abnormalities in the baby or diabetes in the mother.
After 40 weeks, the fluid level needs to be checked regularly to ensure that there is not too steep a decline in fluid levels. If the overdue baby is thought to be at risk, an induction will be recommended.
Insomnia is a common problem during pregnancy and can lead to fatigue, feelings of stress and anxiety, and irritability. Whether it's brought on by your increased size, back pain, heartburn, getting up to empty your bladder, or something else, insomnia is not fun. Taking a warm bath or having a small snack before bed may help, as can relaxation techniques, such as deep breathing. A calming scent in a potpourri or fragrance on your pillow may aid relaxation. Make sure to exercise during the day. If you still can't sleep, get up and do something relaxing: read a book, watch TV, or listen to calming music until you feel sleepy. And try to make up for lost sleep with daytime naps.
Excerpted from Pregnancy Day by Day.
Copyright © 2008 Dorling Kindersley Limited.
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