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A Guide to Third Trimester Prenatal Testing & Screening

As you enter your third trimester, your prenatal appointments should take place more frequently, and will typically be scheduled every other week after the 28th week until you give birth to your baby. Some doctors might ask you to come in every couple of days to monitor your progress more closely if you pass your 41st week of pregnancy. Below are some common tests that your doctor will probably have you take during this trimester.

Fetal Non-Stress Test (NST)
Simple and non-invasive, the non-stress test is performed after the 28th week of pregnancy to screen for fetal activity and ensure the wellbeing of the fetus during the later stages of gestation. NST helps determine whether the baby isn't receiving adequate amounts of oxygen due to placental or umbilical cord problems and can detect other types of fetal distress. It is usually performed if the baby does not move as often as it normally does, the mother is overdue, the doctor suspects that the placenta isn't functioning well, or the mother is at high risk for any other reason. This test poses no threats to the mother's or baby's health and is painless.

Biophysical Profile (BPP)
The biophysical profile is a two-part diagnostic test involving both an ultrasound to examine fetal health and a non-stress test (NST) to record fetal heartbeat and uterine contractions. It is designed to evaluate the level of risk the fetus's health is in during the third trimester, and is generally performed after the 32nd week of pregnancy. The BPP test is ordered when previous screenings indicate the possibility of a fetal health problem or if the pregnancy is considered to be high risk. BPP examines the baby's breathing, movement, muscle tone, heart rate, and amniotic fluid to present an overall picture of the baby's wellbeing and helps your doctor determine whether your baby should be born sooner than scheduled. The BPP poses no known risks to the mother or the baby and is painless.

Group B Strep (GBS) Test
Some women are carriers of the group B strep (GBS), a bacterial illness that can infect babies if not treated and potentially put the fetus's health in critical danger. The doctor will test for GBS by taking a swab sample from the mother's vaginal or rectal area by the 35th week of gestation; if the results come out positive the mother will usually be given intravenous antibiotics during labor to protect the baby from becoming infected with the bacterium.

Rh Disease Blood Test
Each person falls under one of the four blood types, A, B, AB or O, and has either a positive or negative Rh factor which determines their blood cells' characteristics. If a person is Rh positive, it means that they are carriers of the Rh factor protein, and those who are Rh negative are non-carriers. Rh disease occurs when the mother's blood type is incompatible with that of her baby, and even though Rh incompatibility doesn't usually pose a problem during the first pregnancy, if the mother's and baby's blood intermingle during labor the mother's body will register the baby's Rh protein as a foreign substance and will attempt to destroy it by producing antibodies, which could critically threaten the baby's wellbeing. That is why an Rh status blood test is usually conducted after the 28th week of pregnancy to check for antibodies and determine whether you need to be given an Rh-immune globulin injection if you are Rh negative.