While many pregnancies proceed through the nine months without a hitch, others are complicated by maternal or fetal disorders. Prenatal testing is done to prevent or treat complications that may impact the mother or baby. Some prenatal testing is done in the first trimester; other tests are done later in pregnancy.
Blood Types
Blood types are inherited; some blood types make antibodies against other types that can destroy red blood cells. If a mom and baby have different blood types, the baby can be damaged by maternal antibodies. This is especially likely in moms with Rh negative blood whose babies are Rh positive. RhoGAM, which contains Rh positive antibodies, is given to Rh negative moms during pregnancy as a type of vaccination that prevents the mothers from forming antibodies. Knowing if a pregnant woman is Rh negative is essential to prevent severe disease in her baby or in future pregnancies. RhoGAM is given at 26 to 28 weeks of pregnancy, and again after delivery, the University of Rochester Medical Center states.
Diseases
Most doctors test to see if a woman has diseases that might infect her baby at the time of delivery or during pregnancy. Some of the diseases doctors test for include syphilis, toxoplasmosis, HIV, group B strep, hepatitis B and genital herpes. Most doctors also test to see if you're immune to rubella, a disease that can cause miscarriage or serious birth defects if you contract it during pregnancy.
Glucose Testing
Gestational diabetes poses significant risk to both mother and baby. Fasting blood sugars test the level of glucose in the blood after not eating or drinking for eight hours. If your level is higher than normal, you may be given a blood test to check your sugar levels after drinking a drink high in glucose. Abnormally high glucose levels may indicate gestational diabetes. Babies born to moms with gestational diabetes may be larger than normal and have difficulty during and after delivery.
Alpha Fetoprotein Testing
AFP is a blood screening test that measures the level of alpha fetoprotein, a substance produced by the baby's liver and gastrointestinal tract. The test is not diagnostic for certain disease; it suggests only an increased risk, according to the American Pregnancy Association (APA). Low levels may be associated with chromosomal abnormalities such as Down syndrome or other trisomies. Neural tube defects, abnormal openings in the spine, may cause high levels of AFP. Multiple pregnancies also cause high AFP levels; a pregnancy that's not as far along as previously thought may cause lower-than-normal levels, the APA states. AFP testing is usually done around the 16th to 18th weeks of pregnancy.
Ultrasound
Ultrasound is usually done around 18 weeks to check for fetal abnormalities. The nuchal, or neck, thickness may be measured, because babies with Down syndrome often have increased nuchal thickness. Leg length is measured to check for normal growth. If any abnormalities are found, a more thorough examination, known as a level 2 ultrasound, is usually done.
