At this early stage, all your unborn baby's needs will be met by the yolk sac. Attached to the embryo by a connecting stalk, this essential balloonlike structure indicates the site of your pregnancy and can usually be seen as early as this week as a sphere 0.1-0.2 in (3-4 mm) across. At first the yolk sac is as large as the disk of embryonic cells that will eventually become your baby.
Containing cells that perform a similar function to the liver, the yolk sac releases several pregnancy hormones and produces the embryo's first red blood cells. After week 9 the liver will take over these functions as the yolk sac gradually disappears and the placenta takes over, by around the 10th week of pregnancy.
Over the next seven days, a primitive circulatory system develops, well before any blood circulates to the placenta in the 10th week. And, by the end of this week, using the highest quality ultrasound equipment, it is just possible to see the embryo's heartbeat. At this early stage, the heart is simply a tube.
You should continue to take a 400 mcg folic acid supplement daily until the 12th week of pregnancy.
This supplementation is in addition to a well-balanced diet that includes green vegetables and legumes. Many fortified cereals also contain folic acid, as do some fruits, such as oranges, papaya, and bananas.
Unfortunately, pregnancy is by no means a licence to eat anything and everything you'd like. "Eating for two" is a myth, and if you do so, you'll end up consuming too many calories and gaining too much weight. The best advice is to use your common sense. Studies show that pregnant women who eat according to their appetite naturally eat the proper amount and gain a healthy amount of weight.
Caloric needs in pregnancy vary greatly from woman to woman, depending upon pre-pregnancy weight and physical activity. In general, energy needs increase by approximately 300-500 calories per day during pregnancy. In the first trimester, caloric needs are a bit less, more at the lower end of the range.
In the first trimester, when up to 80 percent of women are nauseous or vomiting, getting enough calories can sometimes be a challenge. Like many pregnant women, you may feel most nauseous when your stomach is empty. One good trick is snacking. Eating five small meals rather than three large ones can be soothing to a nauseous stomach, while at the same time giving you the calories you need.
Excerpted from Pregnancy Day by Day.
Copyright © 2008 Dorling Kindersley Limited.
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