Routine Labs and Testing

 

At Initial Visit – Initial Prenatal Labs

 

Routine Labs: The routine prenatal lab panel consists of routine blood count, a test for rubella antibodies, the pap smear, genital cultures, a test for syphilis, hepatitis B, HIV, blood type and antibody screen.  Other testing if necessary might include a sickle cell screen.  The American College of Obstetrics and Gynecology and The American Academy of Pediatricians recommends routine HIV testing in pregnancy.

 

Cystic Fibrosis: In addition, there is an optional blood test for Cystic Fibrosis that each patient can choose to have, if desired.   Cystic Fibrosis is a genetic disorder that can cause respiratory problems, digestive problems, and infertility. Severity of illness can vary.   Cystic fibrosis is an inherited chromosomal disorder and its inheritance is recessive.  As a result, both parents must be carriers to have an affected child.  Carriers of cystic fibrosis are asymptomatic.  If both parents are carriers of cystic fibrosis then there is a 25% chance of having an affected child.  The incidence of carrier status varies based on ethnicity.  Approximately 1 in 25 people of European descent and 1 in 30 Caucasian Americans is a carrier of a cystic fibrosis mutation.  Although less common, 1 in 46 Hispanics, 1 in 65 Africans, and 1 in 90 Asians will carry at least one abnormal CF gene.  There are many mutations in the cystic fibrosis gene.  We are currently able to test for the 32 most common mutations.  So, if you carry a gene mutation which isn’t included in this panel, carrier status may be missed.  If you do test positive as a carrier of the gene, the next step is to test the baby’s father.  If the baby’s father tests negative, the chance of having an affected child is less than 1%.

 

Parvovirus: – Parvovirus B19 is a common virus that infects humans.  The most common illness caused by the virus is ‘Fifth Disease’, which usually effects children and causes a ‘slapped-cheek’ rash on the face and sometimes a rash on the limbs, which resolves in about 7-10 days.  After being exposed once, a person is immune to the virus and will not be affected again.  About 50% of women are immune to the virus, so re-exposure in pregnancy will not be a concern.  However, if a woman is exposed for the first time in pregnancy, there is a small risk of complications with the unborn baby, a risk of less than 5%.  There is a blood test available that can test to see if a patient is immune to Parvovirus, which can be helpful to know for those patients who are at an increased risk of exposure, like preschool employees, teachers, and healthcare workers   There is no immunization available for this virus but if you are not immune you can be aware and avoid exposure to the virus during your pregnancy.

 

11-13 weeks – First Trimester Screen with Nuchal Translucency (NT)

 

This is an optional genetic screen, which consists of a blood test and ultrasound.  The blood test measures the levels of three proteins in your blood.  A trained sonographer will then measure the amount of fluid in the back of the baby’s neck, referred to as the nuchal translucency.  Combining the results of the blood work and the ultrasound measurement, along with information about you including your age and weight, can determine if your baby is at an increased risk of having Down’s syndrome or Trisomy 18. This screen detects Down’s syndrome in 82-87% of cases.

 

11-13 weeks – Chorionic Villus Sampling

 

Another optional genetic test, CVS is a procedure performed between 10 and 13 weeks by a perinatologist.  During the procedure, a small piece of the developing placenta is removed either transcervically or transabdominally.  The cells are then analyzed to determine if the baby has a chromosomal abnormality, like Down’s syndrome or Trisomy 18.  CVS identifies about 99% or chromosomal abnormalities, but there are some risks associated with the procedure.

 

15-21 weeks – Additional genetic screening tests, AFP and Quad Screen

 

The AFP and Quad Screen are blood tests that are offered between 15-21 weeks gestation.  They are optional genetic screening tests.  For those patients who have had the First Trimester Screen with Nuchal Translucency to assess for chromosomal risk, only the AFP blood screen will be done at this time.  This screen assesses for an increased risk of neural tube defects.

 

The Quad Screen is offered to patients who have declined the first trimester genetic screen with nuchal translucency.  This is a blood test that screens for an increased risk for neural tube defects and chromosomal abnormalities, like Down’s syndrome and Trisomy 18.  The Quad Screen can predict approximately 75-80% of open neural tube defects.  It can predict approximately 75% of Down’s syndrome cases in women under age 35, and 80% of cases in women age 35 and older.

 

Being that these are just screening tests, they can only tell us if you might be at a higher risk for one of these conditions.  Alone they cannot make a definite diagnosis.  If you do have a positive genetic screening test, further testing may be considered.  Although a negative test greatly reduces the likelihood that your baby has one of these problems, they cannot eliminate the possibility of having a child affected by one of these conditions.  If you do have a positive result, you will be offered options for further confirmatory testing, including an ultrasound and amniocentesis, performed by a perinatologist.

 

18-22 weeks – Complete OB Ultrasound

 

We offer an ultrasound to all patients between 18 and 22 weeks.  This gives an opportunity to take a detailed look at how the baby is developing, and to detect any abnormalities.  It is at this ultrasound that a patient can find out the gender of the baby, if the genitals can be clearly seen by the sonographer.

 

For patients who are 35 years or older, or patients with a family history of any developmental abnormalities, a Level 2 ultrasound will be scheduled at a maternal fetal medicine office in the area.  The Level 2 is simply a more detailed survey of the fetal anatomy.

 

15-20 weeks – Amniocentesis

 

Amniocentesis is the gold standard in the diagnosis of chromosomal abnormalities and neural tube defects.  It is performed between 15-20 weeks.  During this procedure, a thin needle is inserted into the uterus through your abdomen.  A small amount of fluid is removed and analyzed.  99% of chromosomal abnormalities and 98% of spina bifida can be diagnosed with this test.  There is a slight risk of miscarriage, less than 1%, with an amniocentesis.

 

24-28 weeks – Screen for diabetes in pregnancy and anemia

 

Glucose Challenge Test – The likelihood of developing diabetes increases during pregnancy.  This is because of the hormones produced by the placenta.  The good thing is that diabetes in pregnancy is short lived and almost always resolves after the delivery.  The screening test for diabetes in pregnancy is called the one hour glucose challenge test.  It is usually done between 24-28 weeks.  You will be given a drink called glucola, which has 50 grams of sugar in it.  We check your blood sugar one hour later by blood draw.  A passing value is 140.  Being that this is a screening test, it does have false positives.  The confirmatory test is the three hour glucose challenge test.  This is only done for people who have an abnormal one-hour value, and is performed at an outside lab facility.

 

When you are having your glucose challenge test, we will also draw labs to recheck your Hemoglobin and Hematocrit, which lets us know if your iron is low, meaning that you are anemic.

 

35-36 weeks – Group Beta Strep

 

This is a test done between 35 and 36 weeks.  This culture is looking for bacteria called beta strep.  It is a normal bacteria that is sometimes found in our bodies.  Approximately 10-30% of people are carriers of beta strep.  Carrier status can vary so even if you were negative with a previous pregnancy you could be positive for this in the current pregnancy.  Once you have tested positive, we always consider you a carrier of beta strep.  If you are a carrier, we will treat you with IV antibiotics during labor.

Additional testing and follow-up may be indicated and a provider will discuss this with you as needed throughout the pregnancy.