Question | Answer |
A typical uncomplicated pregnancy lasts 40 weeks calculated from | the last menstrual period (LMP) |
About ten weeks after LMP the embryo contains most of the organs and is referred to as | a fetus. |
The placenta produces several hormones that help sustain the pregnancy, HCG is one of the hormones and used to determine | pregnancy in the laboratory. |
HCG triggers the corpus luteum to produce | progesterone and estrogen. |
HCG helps maintain the uterine lining, the endometrium with an adequate blood supply until | placental production of progesterone begins. |
Initially HCG levels raise exponentially more than doubling each week during the first | weeks of a normal pregnancy. |
The detection level for pregnancy is usually set at | 10 U/L a lot of labs will use 0-5 as negative and 5-10 as gray zone with a comment to repeat testing in a few days. |
Initially HCG levels raise exponentially more than doubling each week during | the first weeks of a normal pregnancy. |
The detection level for pregnancy is usually set at | 10 U/L a lot of labs will use 0-5 as negative and 5-10 as gray zone with a comment to repeat testing in a few days. |
Qualitative can usually be done on BOTH serum and urine. Quantitative are ONLY performed on | serum, not urine. |
Qualitative can usually be done on BOTH serum and urine. Quantitative are ONLY performed on | serum, not urine. |
HCG levels are always used in conjunction with | history, physical examination and ultrasound to detect pregnancy complications, or miscarriage. |
Falling HCG levels may signal | fetal demise. |
Multiple fetus’s can cause higher values of | HCG than a single fetus, ultrasound can help distinguish this. |
A decrease in progesterone levels can lead to | miscarriage. |
The occurrence of down syndrome and open neural tube defects are frequent enough to warrant | prenatal testing for these disorders. |
The tests usually included in this screening are: alpha fetoprotein (AFP), Estriol, and HCG. This is referred to as | a triple screen. |
It takes in to account mothers age, diabetes status, number of fetus’s, weight and the lab values for all of these tests to predict the chance the fetus has | either down syndrome, trisomy 18 or a neural tube defect. |
Some of the more ubiquitous tests are: Phenylketonuria (PKU), Galactosemia, Tyrosemia, Homocysteinuria, sickle cell, and branched chain amino acid disorders. (Including Maple syrup urine disease (MSUD)These tests are performed on | filter paper that is soaked with blood from the babies heel, 24 – 48 hours after birth and tested at the state lab. |
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It should be noted that Neonates, Babies, Children and adolescents can all have | separate reference ranges for some testing. |
Due to these being small dynamic age groups only practices that focus specifically on certain groups have | reference ranges for them. |
Some chemistry testing may be performed on amniotic fluid. This is rare as this testing is | invasive and only done as a last resort. |
Testing for amniotic fluid may be done for | fetal lung maturity testing. |
Remember that surfactants coat the inside of the alveoli normally and prevent them from | collapsing when air is expelled. |
In the mature fetus the pulmonary surfactant is rich in a compound called phosphatidylcholine (lecithin) and phophatidylglycerol (PG) these substances may be measured quantitatively by themselves or | in a ratio to another lipid sphingomyelin that is relatively constant. |
This is termed an L/S ratio, and a ratio of greater than | 2 to 1 would indicate mature lungs |
Lamellar bodies are a storage form of surfactant and are similar in size to normal platelets. These can be done on any cell counter but must be | verified and getting enough samples to do the verification is hard. |
Predictive value of negative result = | TN/(TN+FN) x 100 |
Predictive value of positive result = | TP/(TP+FP) X 100 |
Predictive value of positive result = | TP/(TP+FP) X 100 |
False negative rate = 100% - %sensitivity | |
True-neg rate = diag specificity = | TN/(TN +FP) X 100 |
True-Pos rate = diag sensitivity = | TP/(TP + FN) X 100 |