Third Trimester of Pregnancy Prenatal Testing - Pregnancy & Baby Plus

Ah, your belly's bulging, your baby's growing and you know you're in the home stretch now. But before you go into labor and cross that pregnancy finish line, you have a few more tests to look forward to. Some of the third trimester tests are repeats from the first and second trimesters, but they take on new importance as you get ready to deliver. Here's a rundown of testing to expect in your third trimester of pregnancy.

Urine Analysis and Culture

At 26 to 28 weeks' gestation, another urine culture is collected to identify any bacteria that could increase your risk for preterm labor. If you've been identified as having complications, including gestational diabetes, kidney disease and preeclampsia, you've been getting urine analysis and cultures all along. If not, you likely haven't had one since the first trimester. No matter which category you fall into, you'll need a urine culture during your third trimester.


This last hemoglobin/hematocrit measurement will also be done at 26 to 28 weeks. At this point, your iron stores should have bounced back after the normal second trimester dip. Just like in the first trimester, anemia at this point is defined as a hemoglobin concentration less than 11 g/dL (hematocrit 33%).

This will be your last blood sample, unless there's a need for another hemoglobin test at 36 weeks.

Rh Antibody Test

If you tested Rh negative in your first trimester, you'll be given an Rh antibody test around 26 to 28 weeks. All Rh-negative unsensitized women should receive 300 micrograms of RhoGAM, the Rh immunoglobulin, at 28 weeks to help prevent isoimmunization, an immune reaction to your Rh-positive baby's blood. Right after your baby's born, he'll be Rh factor tested as well, and you'll receive another dose of RhoGAM within 72 hours of delivery if your baby tests Rh positive.

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