First Trimester Tests During Pregnancy

Here are some tests you may undergo during the first trimester of your pregnancy:

Blood tests: During one of your initial exams, your doctor or midwife will identify your blood type and Rh factor, screen for anemia, check for immunity to rubella (German measles), and test for hepatitis B, syphilis, and HIV. Depending on racial, ethnic, or family background, you may be offered tests and genetic counseling to assess risks for diseases such as Tay-Sachs, cystic fibrosis, and sickle cell anemia (if these weren't done at a preconception visit). Tests for exposure to diseases such as toxoplasmosis and varicella (the virus that causes chickenpox) may also be done if needed. Your health care provider may also want to check your levels of hCG, a hormone secreted by the placenta, and/or progesterone, a hormone that helps maintain the pregnancy.

Urine tests: You'll also be asked early on for a urine sample so that your doctor or midwife can look for signs of kidney infection and, if necessary, to confirm your pregnancy by measuring the level of hCG. (A blood hCG test to confirm pregnancy may be used instead.) Urine samples will then be collected regularly to detect glucose (a sign of diabetes) and albumin (a protein that may indicate preeclampsia, which is pregnancy-induced high blood pressure).

Cervical swabs: You'll also have a Pap smear to check for cervical cancer, and vaginal swabs may be taken to test for chlamydia, gonorrhea, and bacterial vaginosis, an infection that can cause preterm birth. Treatment of these conditions will help prevent complications for your newborn.

Chorionic villus sampling (CVS): If you're 35 or older or have a family history of certain diseases, you'll be offered this optional, invasive test usually between 10 and 12 weeks of pregnancy. CVS can detect many genetic defects, such as Down syndrome, sickle cell anemia, cystic fibrosis, hemophilia, and muscular dystrophy. The procedure involves either threading a tiny catheter through your cervix or inserting a needle into your abdomen to obtain a tissue sample from the placenta. The procedure carries a 1% risk of inducing miscarriage and is about 98% accurate in ruling out certain chromosomal birth defects. But in contrast to amniocentesis, it does not help in detecting neural tube disorders, such as spina bifida and anencephaly, or abdominal wall defects.

A promising new procedure that combines a blood test with an ultrasound to screen for Down syndrome may be available between 11 and 14 weeks of pregnancy. The results of a blood test that measures hCG and/or PAPP-A (pregnancy-associated plasma protein A) in maternal blood are used with an ultrasound measurement of the fetus' skin at the back of its neck (called nuchal translucency). The procedure may be able to pick up a substantial portion of Down syndrome cases and other genetic diseases. However, as with all screening methods, a more invasive diagnostic technique like CVS is used to follow up a positive screen.