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Twins Calendar: Conception through Week 12

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Babies’ Growth
Once conception has occurred, the ovum grows from about 3/500 of an inch to a third of an inch within the first four weeks. The heart is the first organ to form, and begins to beat by the end of the third week. By the end of the first month, the heads represent about one third of both embryos, due to the rapid growth of the brain and nervous system. By the end of the second month, both babies have grown to about one inch in length, weighing about 0.14th of an ounce (four grams), and have the early beginnings of arms, legs, ears, eyes, kidneys, and gastrointestinal tracts. Their faces are unmistakably human. From the eighth to the twelfth week, the babies’ lengths have quadrupled and both weights increase tenfold, to be about four inches and one and a half ounces (forty grams). Early in the third month, the buds for the primary (or baby) teeth are present and the nail beds are beginning to form. Their fingers and toes, as well as the external genitalia, are becoming distinct. The babies’ eyelids are formed but closed. As early as the twelfth week, both babies may even start sucking their thumbs.


Mother’s Changes
One sign you might be pregnant is how awful you may feel. Just after conception, you may become nauseous and vomit often, your breasts may be tender and sore, and you may find yourself having to urinate frequently. You may also occasionally feel some rapid heartbeats—an adaptation of your own body to the pregnancy. By ten days after conception (about three and a half weeks after the first day of your last menstrual period, if you are very regular), the human chorionic gonadotropin (HCG) urine test for pregnancy should be positive, confirming your suspicions. These levels are typically even higher with a twin pregnancy and may give an early indication that you are expecting more than one baby. As the hormone levels continue to rise during the second month, your breasts will become larger, firmer, and tender. The breasts may tingle or even throb occasionally. The nipples and pigmented area both become darker.


By this time, the nausea and vomiting has usually subsided. By the end of the tenth week, your blood volume has increased by thirty to forty percent to provide for the needs of the growing babies, uterus, breast tissue, and placenta. Because of this, your pulse will increase by about fifteen beats per minute. Most of this additional blood is concentrated in the pelvic area, so you may experience periods of lightheadedness or even faint when you stand up suddenly. You will also be more prone to nosebleeds and nasal congestion during this time.


Multiple Facts


  • Twins are typically born at thirty-five to thirty-six weeks gestation. Fifty-seven percent of twins arrive prior to thirty-seven weeks; 12 percent arrive prior to thirty-two weeks—seven to eight weeks premature.


  • A woman with a normal weight should gain between forty and fifty-six pounds when pregnant with twins.



Diet and Weight Gain
Unlike the advice you receive when pregnant with one child—to eat only 300 extra calories a day—women pregnant with twins need to gain more weight earlier in pregnancy to help thwart premature births. Your early weight gain (by twenty weeks gestation) has a significant positive influence on your twins’ growth from twenty to twenty-eight weeks, and from twenty-nine weeks until birth—a benefit not unlike money in the bank earning interest! This early weight gain in part reflects the growth of the placenta (or placentas)—the critical middle-man for your babies’ nutrition. If the placentas are well-developed and healthy, your twins will flourish. But if you don’t gain enough weight early in your pregnancy—or if you actually lose weight—your babies’ growth in the second and third trimesters may be slower, which will increase your risk for premature labor.


For women who are underweight before their twin pregnancies, this early period is especially critical. Even women with a body mass index (BMI) above the normal range need to gain appropriately, especially during this early period. If you’re experiencing nausea severe enough to keep you from eating and staying hydrated, ask your health professional to prescribe an anti-emetic.


Eating For Three
During the first trimester, from conception to the twelfth week of pregnancy, 70 percent of the nutrients you supply to your unborn babies are devoted to their brain growth and neurological development. An adequate intake of folic acid now helps to prevent birth defects such as spina bifida. All vital organs are forming at this time, and folic acid promotes their proper growth. Good sources of folic acid (also called folate or vitamin B9) include fortified rice, pasta, breads, cereals, and grains; poultry; lentils and beans; green leafy vegetables; avocados; oranges; and papayas. Try doubling up the beans in your favorite chili recipe, adding avocados to your tacos, and topping your salads with diced peppers and chickpeas.


The other B-vitamins are also important during the first trimester because they too are involved in the formation and growth of all tissues. B-vitamins are known as water-soluble vitamins because they are not stored in the body for very long. That means you must eat a steady supply to promote your babies’ optimal growth. Here is a list of the B-vitamins you need and the foods that provide them:


  • Thiamin (B1): beans, enriched whole grains, fish, nuts, peas, pork, soy
  • Riboflavin (B2): dairy foods, green leafy vegetables, legumes, meat, nuts
  • Niacin (B3): dairy foods, eggs, fortified cereals, meat, poultry, shellfish
  • Pantothenic acid (B5): mushrooms, peanuts, salmon, whole grains
  • Pyridoxine (B6): bananas, eggs, fish, legumes, meat, nuts, poultry, yams
  • Biotin (B7): barley, corn, egg yolks, fortified cereals, milk, peanuts, soybeans, walnuts
  • Cobalamin (B12): fish, fortified cereals and breads, grains, meat, nuts, poultry

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