Sep 13, 2010
This week your baby is undergoing some extraordinary changes and developments. The head, heart, spinal cord, and some of the larger blood vessels begin to form. As these blood vessels form, the heart begins to pump fluid through them, and your baby's first red blood cells are created. Your baby is about 7 - 9 mm or 0.27 - 0.35 inches in length, (approximately the size of a grain of rice), and weighs about 1/30 of an ounce - less than a breath mint.
Your baby's brain, bladder, tongue and esophagus are all developing and transforming, while his eyes are moving to the front of the face and his tiny eyelids are forming. The bones of his tiny limbs have started to form and all of your baby's major organs - heart, intestines, kidneys, liver, lungs and pancreas -- are forming and growing. In fact, your baby actually goes through 3 sets of kidneys during development with this week's development, being the second set.
Both the hand plates and the genital tubercle are present this week, but you can't tell whether it's a boy or a girl by sight at this point. Nasal pits are also forming. In your womb, your baby has already become active swimming around inside the amniotic sac and kicking. However, as he's much too small and well-cushioned by the uterus and the new amniotic fluid you won't be able to feel him yet. But don't worry. In a few months you'll be able to feel him constantly.
Magnified, the embryo is seen with head, rudimentary eye, arm and hand, swimming in the fetal sac. The yolk sac, visible in the foreground, is the embryo's blood-cell factory
With its grotesquely large head and tail - and with the clearly demarcated vertebrae - the 4 1/2 week embryo resembles a prehistoric animal more than anything else. Beneath the rudimentary eye, the branchial arches and the heart; arm and leg buds are also seen. The length of the embryo is 6 mm (1/4 inch).
Five days later, the embryo has almost doubled in its length and is now growing a millimeter a day. Here it is seen in its home environment, the amniotic sac, and suspended in its soft shock absorber, the amniotic fluid. The round ball under the head is the heart, and to the left are the backbone's developing vertebrae and the tail.
The placenta rapidly works its way into the endometrium and its blood vessels. It may be likened to a busy freight terminal: here, nourishment is absorbed from the mother's blood and the embryo rids itself of waste products from its own metabolic system.
(1) The Placenta with the umbilical cord.
(2) The outer fetal membrane, the chorion.
(3) The yolk sac.
(4) The inner fetal membrane, the amnion.
(5) The embryo's head end, with its rudimentary brain and eyes.
(6) The fetal heart.
(7) The beginning of a backbone.
An embryo just over 5 weeks after conception. It's length is one centimeter (0.4 inch) long. The heart and liver are strikingly large in relation to the body. The hands and feet are as yet merely small buds.
During the fifth and sixth weeks the face, trunk and limbs continue to grow. The head, which has until now been sharply inclined forward, straighten up, as does the whole embryo. There are still no skull bones,so one can see straight into the embryonic brain. Two large swellings on the forehead will become what is called the cerebrum, and three other small bulges will form various important portions of the brain. The head is almost grotesquely large compared with the rest of the body, for the embryo's growth takes place from the head downward. It is not until much later in life that the body really catches up. Even in the newborn infant the head is still roughly one-quarter of the body length, while in the adult it is only one-eighth.
Embryo's head and face at 5 1/2 weeks after conception and some 14 mm (about 1/2 inch) long. The eyes, nose and mouth are beginning to show.
The arms and legs are, as yet, extremely short, but hands and feet are starting to take shape. They look as if they are attached directly to the trunk. The hands develop considerably faster than the feet, and this difference also persists for a long time: the infant learns to grasp objects long before it can walk. The time schedule of physical development is precisely programmed and varies little between individuals, although the genetic blueprint may vary considerably in other respects.
Early miscarriages that occur before the woman even knows she is pregnant are very common. This usually means that chromosomes are damaged, or that there are too few or too many. The barrier built into the ovum wall to prevent more than one sperm from fertilizing serves to prevent such flaws in its further development. Ova fertilized by two or more sperm may grow to a relatively advanced stage but, since too much genetic material has entered the ovum, eventually development goes wrong. This is one cause for early miscarriage. Another reason for miscarriage, one that is not especially unusual, is a sperm with some defect in its chromosomal composition. Thus, miscarriage is often nature's way of protecting itself against genetic deviations; and sperm are, in fact, more often the cause than the ovum.