Your Baby: The Start Of Thumb Sucking
At this stage, your fetus weighs approximately 1.75 ounces (50 g) and measures just over 4 inches (10.2 cm). Hair is sprouting everywhere. The fetus gets fine hair all over to protect it from the constant exposure to the amniotic fluid. Skin formation is progressing, but is very thin (you can even see small blood vessels forming underneath). At this point, the baby might even be sucking its thumb!

Your Body: The ABCs Of The AFP

• What is an AFP? The AFP is a blood test that measures the levels of alpha-fetoprotein in the mother's blood or serum. Also called maternal-serum alpha-fetoprotein (MSAFP), this test is part of the triple screen that measures the fetus-produced substance, as well as two others that are present in pregnant women -- human chorionic gonadotropin (hCG), a hormone produced in the placenta; and unconjugated estriol, an estrogen produced by both the fetus and the placenta.
• When is the test taken? To get the most accurate results of the AFP, the test should be done between 15 and 18 weeks after the first day of your last menstrual period.
• What is the purpose of the test? The triple screen is performed to show whether your fetus is at a greater risk for having a neural tube defect, but it can also help screen for chromosomal defects. Abnormal levels of AFP, both high and low, may indicate some sort of birth defect. A level that is high may indicate a neural tube defect (such as spina bifida), and a low level could indicate Down's syndrome.
• How safe is it? The blood test is like any other maternal blood test and poses no harm to the mother or the fetus. The real risk is that a false-positive result may require further testing -- such as amniocentesis -- a more invasive procedure.
• How reliable are the results? The triple test is a screening tool used to identify women at increased risk for fetal problems. Therefore, it is a very sensitive test. That means there may be high false-positive results. In fact, only 60% of the positive results are accurate. That means the other 40% are false-positives (abnormal test results, but a normal baby). A higher- or lower-than-average result can be attributed to an incorrect estimation of the age of the fetus; twins (both babies produce the substance); or not taking into account your weight, race, or the presence of diabetes.

Weekly Tip
Take the Alpha-fetoprotein (AFP) test on the early side of the window in case you get a false-positive or false-negative result, and there is a need for further testing. That way, you'll have plenty of time to get genetic counseling, do a more in-depth ultrasound, and take the amniocentesis, if you so choose. Read on to learn more about the AFP.