4 Proceso de Modelado
4.1 Exterior del Hawker Hurricane
4.1.10 Sistema de Escape
Dear Tori,
My doctor’s nurse phoned this week to ask if I knew that my blood type was Rh-negative. I had been told this years ago but had forgotten about it. The nurse said that if my husband is also Rh- negative (we will find out this week), I have nothing to worry about. If he is not, I have to receive a shot at 28 weeks. Can you please explain why this is necessary?
Stephanie, Iowa
Dear Stephanie,
Rh factor, or Rh antigen, is a substance present by hered- ity in the blood of most people. Only 15 percent of us lack Rh factor, or have Rh-negative blood. Years ago, babies often died from what was known as Rh incompatibility, or rhesus disease. Today, we can prevent this from happening.
If both you and your husband have Rh-negative blood, then the baby will also have this blood type, and no treat- ment is needed. If, however, your blood is Rh-negative and your husband’s is Rh-positive, the baby may have Rh-positive blood. In this case, your body could begin producing anti- bodies to your baby’s red blood cells.
If you have never been pregnant before, your baby would be unaffected by these antibodies. They would remain dor- mant and harmless unless you became pregnant again. Then, if your baby were Rh-positive, the antibodies could cross the placenta and attack the baby’s red blood cells. This could cause anemia and mild to severe jaundice in the baby.
To prevent this problem, an Rh-negative mother with an Rh-positive partner receives a shot of Rh immune globulin, or RhoGAM, at 28 weeks of pregnancy and again within 72 hours of giving birth. Rh immune globulin is also given to an Rh-negative woman after a miscarriage, an ectopic preg- nancy, or an induced abortion, and at the time of amniocen- tesis, CVS, or another invasive procedure during preg- nancy. A shot of RhoGAM should be considered, too, if an Rh-negative woman experiences any significant bleeding or blunt trauma, such as from a car accident or fall, while she is pregnant. This kind of injury can also cause Rh sensi- tization.
SLEEPING ON YOUR BACK
Hi, Tori,
I enjoy sleeping on my back, and I have heard that I shouldn’t do this. Can you please tell me why, and at what point in preg- nancy I should stop?
Amy, Maine
Amy,
A major blood vessel known as the inferior vena cava runs up your back from your legs. It is responsible for re- turning blood to your heart. As your uterus and your belly grow, there is increased pressure on this vessel when you are lying flat on your back. You know that you’ve been in this
position too long if you have the sensation that your legs are falling asleep or you just feel uncomfortable. As your preg- nancy progresses, you will probably be more comfortable ly- ing on your side. This position allows maximum blood flow through your body and to your placenta and baby.
We all move around a great deal while we are sleeping. Please don’t worry if you wake up on your back; this is per- fectly normal. Just reposition yourself so that you are com- fortable.
GENETIC COUNSELING
Hi, Tori,
I am 39 years old, and my husband and I are undergoing in- fertility treatment. My doctor has suggested that we see a genetic counselor. Can you tell me a little bit about what genetic coun- selors do?
Sarah, Indiana
Dear Sarah,
A genetic counselor is a specially trained health profes- sional who works with a couple to determine their risk of passing on an inheritable disease to their baby. The coun- selor thoroughly investigates the personal and family health history and ancestry of both mother and father. He or she helps the couple interpret information about a particular disorder, learn about inheritance patterns and the risks that a disease will recur, and review available options.
You might be referred to genetic counseling if any of the following conditions apply:
• You have had an abnormal result on a fetal screening test.
• You are planning an invasive, diagnostic fetal test.
• You or the father has already had a child with a birth
defect or genetic disorder.
• A close family member has an inherited disease.
• You or the father has any family history of mental
retardation, birth defects, or a genetic disease such as muscular dystrophy or cystic fibrosis.
• You and the father are of African, Jewish, Italian, Greek,
or Middle Eastern ancestry.
Particular inherited genetic defects, such as the following conditions or diseases, are more likely to occur among peo- ple of particular ancestry:
Sickle-cell anemia is found among African Americans.
This is a disease in which the body makes abnormally shaped red blood cells.
Tay-Sachs disease occurs in descendants of Central and
Eastern European Jews. This is a fatal disorder in which harmful quantities of a fatty substance called ganglioside GM2 build up in tissues and nerve cells in the fetal brain.
Thalassemia is a blood disorder that occurs in people of
Italian, Greek, Middle Eastern, and Southeast Asian de- scent. People with the disease are unable to make enough hemoglobin and so become severely anemic.
Genetic counseling is unnecessary for most couples, but it can be very helpful if you fall into one or more of these risk categories.
WHEN WILL I START SHOWING?
Tori,
I am currently 131⁄
2weeks pregnant with my first baby. I am so
excited! When can I expect to start showing? My sister is expecting her third baby close to mine, and she is already wearing maternity clothes.
Keisha, Rhode Island
Keisha,
Different women begin to show at different times. When you will start to show depends on your overall body size, your height, your pre-pregnancy weight, and, especially, the length of your midbody. Women with longer midbodies tend to hide their babies longer and look smaller than do other women whose babies are at the same gestational age. Women who have already given birth, as your sister has, tend to show a little earlier in a subsequent pregnancy. How the baby is positioned in the uterus also partly determines how the mother’s body looks.
Most women have at least a little bump by 15 weeks. At first, though, you and your partner may be the only ones to notice your bump. Often, other people don’t recognize that a woman is pregnant until she is about 20 weeks along. Although I am petite, when I was pregnant with Alexander, I did not develop even a bump until 16 weeks. I wore ma- ternity clothes because I was excited, but I really didn’t need them until I was six months along.
Try not to be concerned about comments such as “Oh, you look so small!” (People may be asking your sister, “Wow! Is that just one baby in there?”) No one can tell, just by look- ing at you, what size your baby is.
PREGNANT AND OVERWEIGHT
Tori,
Although I tried to lose weight before conceiving, I started preg- nancy nearly 40 pounds overweight. My doctor has told me that I do not need to gain any weight and that I should just try not to lose any. He has given me suggestions about sensible eating, and I am committed to following them. Besides eating well, I am walking a great deal. I know that much of the weight gained in pregnancy goes to the placenta, baby, extra blood flow, and fluid. How, then, is it possible for overweight women not to gain?
Jamie, California
Dear Jamie,
It is wonderful that you have a sensible approach to weight and nutrition and that you are doing everything pos- sible to keep yourself and your baby healthy.
Obesity in pregnancy is associated with a higher inci- dence of hypertension (high blood pressure), preeclampsia, gestational diabetes, and macrosomic babies (heavier than 91⁄
2pounds). Poor eating habits can cause obese women to
gain even more weight in pregnancy. But overweight women who eat sensibly often discover that they gain very little during pregnancy. With proper diet and exercise, the body redistributes some of the weight. Some of the existing fat stores are used for the baby, the placenta, and breast tis- sue. This can happen without extreme dieting. It’s impor- tant, in fact, not to strictly limit calories during pregnancy and while you are breastfeeding.
If you need help in managing your weight, ask your doc- tor about visiting with a dietitian or nutritionist. He or she can help you develop a healthy approach to eating and nu- tritious meal plans.
DAD’S CORNER
A
t the beginning of the chapter, I mentioned that now, during her third month of pregnancy, the nausea and the extreme fatigue that may have plagued Mom in her first trimester would, hope- fully, be passing. She may be starting to show, too, and you and she may have seen your baby in an ultrasound scan. As things change for your partner, you might notice some changes in yourself. You might be feeling pregnant. Seriously!Breasts 2–3 lbs.
Placenta 1.5 lbs. Blood volume
and body fluids 6 lbs. Uterus 2.5 lbs. Body fat 4–6 lbs. Baby 7–8 lbs. Amniotic fluid 2 lbs. T O TA L W E I G H T G A I N R A N G E 2 5 – 3 5 l b s .
The Couvade
Many partners of pregnant women undergo a se- ries of symptoms and changes that can mimic some of those typical of pregnancy. Most common are mood swings, food cravings, and weight gain. This syndrome, called the couvade, is thought to be ex- perienced by at least 10 percent of partners. It can be a pesky experi- ence, especially for a dad who assumed he was going to observe pregnancy, not share in it.You can take inspiration from cultures that celebrate the couvade all over the world. In southern India, for example, the experience is ritual- ized by dressing the husband in women’s clothes and laying him in a darkened room while his wife is in labor. This practice is believed to protect the laboring mother and her child by distracting evil forces. When the child is born, the father emerges from his “womb” and rejoins his family. In a way, he is born again, as a father instead of a son.
So, if you are one of those partners who wakes bolt upright in bed with leg cramps, it might help to think, as you rub your calves, that there is probably a father-to-be on the other side of the world doing the same thing.