The period from conception to birth. After the egg is fertilized by a sperm and then implanted in the lining of the uterus, itdevelops into the placenta and embryo, and later into a fetus. Pregnancy usually lasts 40 weeks, beginning from the firstday of the woman’s last menstrual period, and is divided into three trimesters, each lasting three months.
Pregnancy is a state in which a woman carries a fertilized egg inside her body. Due to technological advances,pregnancy is increasingly occurring among older women in the United States.
At the end of the first month, the embryo is about a third of an inch long, and its head and trunk-plus the beginnings ofarms and legs-have started to develop. The embryo receives nutrients and eliminates waste through the umbilical cordand placenta. By the end of the first month, the liver and digestive system begin to develop, and the heart starts to beat.
In this month, the heart starts to pump and the nervous system (including the brain and spinal cord) begins to develop.The 1 in (2.5 cm) long fetus has a complete cartilage skeleton, which is replaced by bone cells by month’s end. Arms,legs and all of the major organs begin to appear. Facial features begin to form.
By now, the fetus has grown to 4 in (10 cm) and weighs a little more than an ounce (28 g). Now the major blood vesselsand the roof of the mouth are almost completed, as the face starts to take on a more recognizably human appearance.Fingers and toes appear. All the major organs are now beginning to form; the kidneys are now functional and the fourchambers of the heart are complete.
The fetus begins to kick and swallow, although most women still can’t feel the baby move at this point. Now 4 oz (112 g),the fetus can hear and urinate, and has established sleep-wake cycles. All organs are now fully formed, although theywill continue to grow for the next five months. The fetus has skin, eyebrows, and hair.
Now weighing up to a 1 lb (454 g) and measuring 8-12 in (20-30 cm), the fetus experiences rapid growth as its internalorgans continue to grow. At this point, the mother may feel her baby move, and she can hear the heartbeat with astethoscope.
Even though its lungs are not fully developed, a fetus born during this month can survive with intensive care. Weighing 1-1.5 lbs (454-681 g), the fetus is red, wrinkly, and covered with fine hair all over its body. The fetus will grow very fastduring this month as its organs continue to develop.
There is a better chance that a fetus born during this month will survive. The fetus continues to grow rapidly, and mayweigh as much as 3 lb (1.3 kg) by now. Now the fetus can suck its thumb and look around its watery womb with openeyes.
Growth continues but slows down as the baby begins to take up most of the room inside the uterus. Now weighing 4-5lbs (1.8-2.3 kg) and measuring 16-18 in (40-45 cm) long, the fetus may at this time prepare for delivery next month bymoving into the head-down position.
Adding 0.5 lb (227 g) a week as the due date approaches, the fetus drops lower into the mother’s abdomen and preparesfor the onset of labor, which may begin any time between the 37th and 42nd week of gestation. Most healthy babies willweigh 6-9 lb (2.7-4 kg) at birth, and will be about 20 in. long.