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 examinations, your doctor or midwife will identify your blood type and Rh (rhesus) factor, screen for anemia, check for immunity to rubella (German measles), and test for hepatitis B, syphilis, and HIV and other sexually transmitted diseases.

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 will 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 hCG level. (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, pregnancy-induced high blood pressure).

In the later part of the first trimester you will be offered genetic testing. You first have to decide if you want any genetic testing at all. Some people feel like these tests may cause them undue stress and they prefer to make sure the baby is genetically normal after the baby is born. Some people want to go ahead and do all the testing they can realizing that these tests sometimes are not 100% accurate. Talk with your doctor about the pros and the cons before proceeding to see if genetic testing is right for you and your pregnancy. There are different genetic testing options that involve blood tests alone or with an ultrasound that involve no risk to the fetus. If these non invasive tests are abnormal, then further testing will be offered to you. At that point, you can decide if you want to do those tests or not.

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One first semester genetic test 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 skin at the back of the fetus’ neck (called nuchal translucency). The procedure may be able to pick up a substantial portion of Down syndrome cases and other genetic conditions. However, as with all screening methods, a more invasive diagnostic technique like CVS is used if results are positive.

Non-Invasive Prenatal Testing (NIPT) screening: This cell-free fetal DNA test can be done as early as after 10 weeks of pregnancy. The test uses a blood sample to measure the relative amount of free fetal DNA in a mother's blood. It's thought that the test can detect 99% of all Down syndrome pregnancies. It also tests for some other chromosomal abnormalities.

Chorionic villus sampling (CVS): If you're 35 or older, have a family history of certain diseases, or have had a positive result on non-invasive genetic tests, you will 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.

Be sure to discuss all of your testing options with your doctor so that together you can decide on the ones that will be best for you.

WebMD Medical Reference Reviewed by Traci C. Johnson, MD on February 07, 2015

Sources

SOURCES:

Danforth's Obstetrics and Gynecology, 9th edition, 2003.

Gabbe: Obstetrics-Normal and Problem Pregnancies, 4th edition, 2002.

March of Dimes.

WebMD Medical Reference provided in collaboration with The Cleveland Clinic: "Pregnancy: Chorionic Villus Sampling."

Ob/Gyn Ultrasound at the Fairbanks Clinic, Fairbanks, Alaska.

UCSF Nedical Center: "FAQ: Cell-Free Fetal DNA Testing."

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