PLEASE NOTE: It is not necessary that you print these attachments for Women's Health Care Services, P.A. However, you may print them for your own records.

Development of the embryo and fetus

• The female egg is fertilized by the male sperm and begins to divide and multiply. (This is when birth defects such as Down syndrome may occur.)
• The cluster of dividing cells nests in the lining of the uterus.
  The cluster of cells takes on a flattened, saucer-like shape and is called an embryo.
• Because the embryo has little connection with the pregnant woman’s bloodstream, drugs and alcohol taken now by the pregnant woman may pose less risk to the embryo than during the next 8 weeks.
• Taking prenatal vitamins before conception or starting them as soon as the pregnancy is discovered will help prevent potential problems in development.
• About half of all developing embryos die during the first few weeks because of errors in the genetic instructions for development.

Calculating the length of pregnancy
There are several ways to calculate the length of a normal, full-term pregnancy.

• A pregnancy may be counted in menstrual weeks from the first day of the last menstrual period (LMP). Using this method, a full-term pregnancy lasts 40 weeks.
• A pregnancy may also be tracked in fetal weeks counting from the date of conception. Using this methods a full-term pregnancy lasts 38 weeks.
• Generally, doctors use menstrual weeks from the first day of the last menstrual period. This is because the date of conception is often not known.

Measuring the length of the embryo and fetus
There are a variety of ways to measure the length of the embryo and fetus. One of the most common is called crown rump. The crown rump measurement is based from the top of the head to the bottom of the seat. It does not include the legs which do not accurately reflect early rates of growth and development.

Individual differences
After about 18 weeks of pregnancy, fetal length and weight vary greatly, depending on nutrition, maternal and fetal health, and heredity.

5-6 weeks after the last menstrual period (3-4 weeks after conception)

• The menstrual period is missed or is very light. A pregnancy test is “positive” (hormones of pregnancy can be measured in blood or urine pregnancy).
• A yolk sac nourishes the embryo while the placenta (afterbirth) and membranes (bag of waters) begins to form.
• As the placenta and umbilical cord form, drugs and alcohol from the pregnant woman’s bloodstream may cause problems with the embryo’s development. The flat shape of the embryo folds into a cylinder.
• The spine and head are forming. (This is when spina bifida, a neural defect, may occur in the embryo.)
• The heart is forming and blood circulation begin. (This is when major heart defects may occur in the embryo.)
• Bumps appear where the arms and legs will develop.
  The embryo is smaller then a grain of rice.
• One in 5 pregnancies is lost (miscarried) between 4 and 12 weeks of development.
• There is no chance of survival outside the uterus.

7-8 weeks after the last menstrual period (5-6 weeks after conception)

• The head is over one-half of the body length.
• The ears and eyes are forming and moving toward their proper location on the head.
• The heart is pumping. The heartbeat is visible by ultrasound examination.
• Internal organs (liver, kidneys, intestines) are growing so fast they are pushed out for a time into a bulge in the umbilical cord.
• The limbs are growing longer. The fingers and toes are webbed.
• The embryo grows from 1/5 to 1/2 inches in length.
• There is no chance of survival outside the uterus.

9-10 weeks after the last menstrual period (7-8 weeks after conception)

• The embryo is now called a fetus.
• The sides of the face are moving together.
• The nose and mouth are forming. (This is when cleft lip and cleft palate may occur.)
• The fingers and toes separate and lose their webbing.
• Bones are composed largely of flexible fibers called cartilage.
• Reflex movement is seen on ultrasound.
• The embryo grows from 1/2 to 1 inch in length.
• There is no chance of survival outside the uterus.

11-12 weeks after the last menstrual period (9-10 weeks after conception)

• The fetus takes on a human appearance.
• The face is broad with eyes widely separated.
• The eyelids are formed and fused shut.
• The ears are moving upward from the sides of the neck.
• The kidneys are making urine. (Before this time, the fluid in the “bag of waters” comes mainly from the membranes.)
• Internal organs (liver, kidneys, intestines) are immature.
• The heart rate can be heard with amplification.
• Genetic testing is possible with CVS (chorionic villus sampling).
• The fetus grows from 1 to 2 1/2 inches in length.
• There is no chance of survival outside the uterus.

13-14 weeks after the last menstrual period (11-12 weeks after conception)

• The fetus begins to swallow fluid.
• Outward signs of sex become visible.
• Bones begin to take on a more solid form.
• Joints and muscles allow full body movement.
• Genetic testing is possible with early amniocentesis.
• Between 12 and 40 weeks, 1 in 100 pregnancies ends in miscarriage or stillbirth.
• The fetus grows from 2-1/2 to 4-1/2 inches in length.
• Weight increases from 1/2 ounce to 1-1/2 ounces.
• There is no chance of survival outside the uterus.

15-16 weeks after the last menstrual period (13-14 weeks after conception)

• The simple brain becomes highly complex over the next 10 weeks.
• The inner sex organs are nearly complete.
• The fetus grows from 4-1/2 to 5-1/2 inches in length.
• Weight increases from 1-1/2 to 4 ounces.
• There is no chance of survival outside the uterus.

17-18 weeks after the last menstrual period (15-16 weeks after conception)

• The head is about 1/3 of the total body length.
• Myelin (nerve insulation) begins to form around nerves in the body.
• Hair and nails begin to grow.
• The fetus grows from 5-1/2 to 6-1/4 inches in length.
• Weight increases from 4 to 7 ounces.
• There is no chance of survival outside the uterus.

19-20 weeks after the last menstrual period (17-18 weeks after conception)

• The body is covered with fine, downy hair called lanugo.
• The pregnant woman begins to feel movement and kicking.
• The fetus grows from 6-1/4 to 7-1/2 inches in length.
• Weight increases from 7-11 ounces.
• There is no chance of survival outside the uterus.

21-22 weeks after the last menstrual period (19-20 weeks after conception)

• Eyebrows and eye lashes begin to form.
• The skin is very thin and red with no fat underneath.
• Blood vessels are easily seen beneath the skin.
• The ears are flat, shapeless and bendable.
• The fetus grows from 7-1/2 to 8-1/4 inches in length.
• Weight increases from 11 to 16 ounces (1 pound).
• The chance of survival outside the uterus is less than one in one million.

23-24 weeks after the last menstrual period (21-22 weeks after conception)

• Myelin (nerve insulation) begins to form in the brain.
• The network of nerve connections becomes more complex.
• The fetus grows from 8-1/4 to 9 inches in length.
• Weight increases from 1 pound to 1 pound, 6 ounces.
• At the end of the 24th week, survival rate is 3 percent outside the uterus without application of intensive care services.

25-26 weeks after the last menstrual period (23-24 weeks after conception)

• The sucking reflex begins.
• Fingernails begin to grow.
• The fetus grows from 9 to 9-3/4 inches in length.
• Weight increases from 1 pound, 6 ounces to 1 pound, 13 ounces.
• Survival rate outside the uterus is about 24 percent without application of intensive care services.
• About 75 percent of babies who survive will have major disabilities related to their extreme prematurity.

27-28 weeks after the last menstrual period (25-26 weeks after conception)

• The eyes are partly open and can perceive light.
• Reaction to sound may be observed.
• The fetus grows from 9-3/4 to 10-1/2 inches in length.
• Weight increases from 1 pound, 13 ounces to 2 pounds, 3 ounces.
• Survival rate outside the uterus is about 40 percent without application of intensive care services.
• 25 percent will be born with major disabilities related to their extreme prematurity.

29-30 weeks after the last menstrual period (27-28 weeks after conception)

• The eyes are open.
• Cycles of sleeping, turning, kicking and sucking are becoming established.
• The skin is still slightly wrinkled.
• The fetus can grasp, but muscle tone is very low.
• Fine, wooly scalp hair stands out in tufts on the head.
• The fetus grows from 10-1/2 to 11 inches in length.
• Weight increases from 2 pounds, 3 ounces to 2 pounds, 13 ounces.
• Survival rate outside the uterus is about 90 percent.
• 15 percent will be born with disabilities related to their extreme prematurity.

31-32 weeks after the last menstrual period (29-30 weeks after conception)

• The skin grows thicker and pinker as fat begins to form.
• Lanugo (fine hair) disappears from the face.
• The body begins to fill out.
• Toenails begin to grow.
• The sucking reflex is coordinated with swallowing.
• Head control is beginning.
• The fetus grows from 11 to 11-3/4 inches in length.
• Weight increases from 2 pounds, 13 ounces to 3 pounds, 12 ounces.
• Survival rate outside the uterus is 91 percent.
• 8 percent will be born with disabilities related to their prematurity.

33-34 weeks after the last menstrual period (31-32 weeks after conception)

• The ears begins to curve and hold their shape.
• The fingernails reach the fingertips.
• Muscle tone increases steadily.
• The fetus grows from 11-3/4 to 12-1/2 inches in length.
• Weight increases from 3 pounds, 12 ounces to 4 pounds, 10 ounces.
• Survival rate outside the uterus is about 95 percent.

35-36 weeks after the last menstrual period (33-34 weeks after conception)

• Scalp hair becomes silky and lays flat against the head.
• Neck muscles can raise the head.
• Trunk muscles can raise the head.
• Testes start to move into the scrotum on boys.
• Labial folds nearly cover the clitoris in girls.
• The fetus grows from 12-1/2 to 13-1/2 inches in length.
• Weight increases from 4 pounds, 10 ounces to 5 pounds, 5 ounces.
• Survival rate outside the uterus is greater than 95 percent.

37-38 weeks after the last menstrual period (35-36 weeks after conception)

• Lanugo (fine hair) is gone except on the shoulders.
• Arm and leg muscles are flexed.
• Sucking and rooting reflexes are well established.
• Lungs usually are mature.
• The fetus grows from 13-1/2 to 14-1/2 inches in length.
• Weight is from 5 pounds, 5 ounces to 6 pounds, 5 ounces.
• Survival rate outside the uterus is greater than 95 percent.
  

39-40 weeks after the last menstrual period (37-38 week after conception)

• “Baby hair” on the scalp is replaced by short, fine hair.
• The skin is pink and plump with a generous layer of fat underneath.
• The testes are down in boys; the clitoris is covered in girls.
• The fingernails extend beyond the finger tips and the toenails extend to the toe tips.
• Length from the head to the buttocks is 14-1/2 inches (19 to 21 inches from head to toe).
• Weight increases from 6 pounds, 5 ounces to 7 pounds, 6 ounces.
• Survival rate outside the uterus is greater than 95 percent.

IC Attachment D

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