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Week 28 How Big Is Your Baby? Your baby weighs about 2.4 pounds (1100g). Crown-to-rump length is close to 10 inches (25cm). Total length is 15.75 inches (35cm). How Big Are You? Your uterus is now well above your umbilicus. Sometimes this growth seems gradual. At other times, it may seem as though changes happen rapidly, as if overnight. Your uterus is about 3.2 inches (8cm) above your bellybutton. If you measure from the pubic symphysis, it is about 11 inches (28cm) to the top of the uterus. Your weight gain by this time should be between 17 and 24 pounds (7.7 and 10.8kg). How Your Baby Is Growing and Developing Until this time, the surface of the baby's developing brain has appeared smooth. At around 28 weeks of pregnancy, the brain forms characteristic grooves and indentations on the surface. The amount of brain tissue also increases. Your baby's eyebrows and eyelashes may be present. Hair on the baby's head is growing longer. The baby's body is becoming plumper and rounder. It's beginning to fill out a little because of increased fat underneath the skin. Before this time, the baby had a thin appearance. Your baby now weighs about 2.4 pounds (1100g). This is an amazing growth compared to just 11 weeks ago, when it weighed only about 3.5 ounces (100g) at 17 weeks of pregnancy. Your baby has increased its weight more than 10 times in 11 weeks. In the last 4 weeks, from the 24th week of your pregnancy to this week, its weight has doubled. Your baby is growing rapidly! Changes in You The Placenta The placenta plays a critical role in the growth, development and survival of the baby. The illustration on page 233 shows the fetus attached to the umbilical cord, which attaches to the placenta. Two important cell layers, the amnion and the chorion, are involved in the development of the placenta and the amniotic sac. Development and function of the cell layers is complicated, and their description is beyond the scope of this book. However, the amnion is the layer around the amniotic fluid in which the fetus floats. The placenta begins to form with trophoblastic cells. These cells grow through the walls of maternal blood vessels and establish contact with your bloodstream without your blood or fetal blood mixing. (Fetal circulation is separate from your circulation.) These cells grow into the blood vessels without making a vascular connection (or opening) between the blood vessels. But fetal blood flow in the placenta is very close to your blood flow in the placenta.
We have closely followed your baby's weight gain in this book. The placenta is also growing at a rapid rate. At 10 weeks gestation, the placenta weighed about 0.7 ounce (20g). Ten weeks later, at 20 weeks gestation, it weighs almost 6 ounces (170g). In another 10 weeks, the placenta will have increased to 15 ounces (430g). At full term, 40 weeks, it will weigh almost 1.5 pounds (650g)! Connections are made between fetal blood vessels and the developing placenta as early as the 2nd or 3rd week of development. During the 3rd week of gestation, projections (villi) at the base of the placenta become firmly attached to the underlying layer of the uterus. Villi are important during pregnancy. The space around the villi (intervillus space) becomes honeycombed with maternal blood vessels. The villi absorb nutrients and oxygen from the maternal blood; these are transported to the growing baby through the umbilical vein in the umbilical cord. Waste products from the baby are brought through the umbilical arteries to the intervillus space, and are transferred to the maternal bloodstream. In this way, the baby gets rid of waste products. What Does the Placenta Do? The placenta is involved in moving oxygen and carbon dioxide to and from the baby. It is also involved in nutrition and the excretion of waste products from the baby. In addition to these functions, the placenta has a very important hormonal role. It produces human chorionic gonadotropin (HCG) (discussed in Week 5). This hormone is found in your bloodstream in measurable amounts within 10 days after fertilization. Pregnancy tests check HCG levels to determine if a woman is pregnant. The placenta also begins making the hormones estrogen and progesterone by the 7th or 8th week of pregnancy. What Does the Placenta Look Like? At full term, a normal placenta is flat and has a cakelike, round or oval appearance. It is about 6 to 8 inches (15 to 20cm) in diameter and 0.8 to 1.2 inches (2 to 3cm) thick at its thickest part. It weighs between 17.5 and 24 ounces (500 to 650g) on average. Placentas vary widely in size and shape. A placenta that is too large (placentamegaly) can be found when a woman is infected with syphilis or when a baby has erythroblastosis (Rh-sensitization of the baby). Sometimes it occurs without any obvious explanation. A small placenta may be found in normal pregnancies but may also be found with intrauterine-growth retardation. The part of the placenta that attaches to the wall of the uterus has a beefy or spongy appearance. The fetal side of the placenta, the side closest to the baby inside the amniotic sac, is smooth. It is covered with amniotic and chorionic membranes. The placenta is a red or reddish-brown color. Around the time of birth, the placenta may have white patches on it, which are calcium deposits. In multiple pregnancies, there may be more than one placenta. Or there may be one placenta with more than one umbilical cord coming from it. Usually with twins, there are two amniotic sacs, with two umbilical cords running to the fetuses from one placenta. The umbilical cord, which is the attachment from the placenta to the baby, contains two umbilical arteries and one umbilical vein, which carry blood to and from the baby. It is about 22 inches (55cm) long. The cord is usually white and contains large blood vessels. A few women experience problems involving the placenta during pregnancy. These include placental abruption (see Week 33) and placenta previa (see Week 34). After delivery, a retained placenta is sometimes a problem (see Week 38).
How Your Actions Affect Your Baby's Development Dealing with Maternal Asthma Asthma is a respiratory illness characterized by an increased responsiveness or sensitivity to stimulation of the trachea and the bronchi, both important to breathing. Problems with asthma are manifested by difficulty breathing, shortness of breath, coughing and wheezing. (Wheezing is a noise like a whistling or a hissing made as air moves through narrowed airways.) Asthma comes and goes, with acute worsening of symptoms interspersed with symptom-free periods. It affects about 2% of the population in the United States and Canada. It is equally common in other countries. It may occur at any age, but about 50% of all asthma cases occur before age 10. Another 33% of the cases occur by age 40. Pregnancy does not seem to cause any consistent, predictable problem with asthma. Some pregnant women appear to get better during pregnancy, while others remain about the same. A few get worse. Treating Asthma Attacks Most pregnant women with asthma can have a safe pregnancy, labor and delivery. If a woman has severe asthma attacks when she isn't pregnant, she may have severe attacks during pregnancy. In general, the treatment plan used before pregnancy will probably continue to be helpful. This includes medications prescribed for asthma before or during pregnancy. During pregnancy, oxygen consumption increases by about 25%. Your baby needs oxygen to grow and to develop. That's why asthma treatment is so important while you're pregnant. Asthma medication, such as terbutaline, and steroids, such as hydrocortisone or methylprednisolone, can be used during pregnancy. Aminophylline or theophyline may also be used. Leeanne was concerned about her asthma and wanted to know what she could do for it that didn't require medication. I told her that many women have found they can help themselves with their asthma during pregnancy fairly easily. Maintaining good hydration with more-than-adequate fluid intake seems to help many women. You Should also Know Additional Testing Twenty-eight weeks of gestation is a time when many doctors initiate or repeat certain blood tests or procedures. Glucose-tolerance testing may also be done at this time. How Is the Baby Lying? It is common at this point in pregnancy to ask your doctor which way the baby is lying. Is the baby head first? Is it bottom first (breech)? Is the baby lying sideways? It's difficultùusually impossibleùat this point in pregnancy to tell just by feeling your abdomen how the baby is lying and if it is coming bottom first, feet first or head first. The baby changes position during pregnancy and may continue to change its position for another month. It doesn't hurt to try to feel the abdomen to see where the head is and where the abdomen is. In another 3 to 4 weeks, the baby's head will be harder, and it will be easier then for your doctor to determine how the baby is lying (called presentation of the fetus). Previous Week > Contents > Next
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