Human Placental Lactogen (hPL) test is used to evaluate the adequacy of the placenta in high-risk pregnancies.The human placenta secretes several types of hormones which are homologous to the hormones of the Anterior Pituitary. Human Placental Lactogen (hPL), whose task is to maintain the pregnancy, is structurally similar to both human prolactin and growth hormone. This cause Human Placental Lactogen to have stimulating nature on both lactogenic and growth hormones.
Serum Human Placental Lactogen levels normally increase very early in pregnancy. Measurement of Human Placental Lactogen levels during pregnant is very helpful to monitor placental function. Human Placental Lactogen levels are also helpful to assist pregnancies accompanied by hypertension, proteinuria, edema, postmaturity, placental insufficiency, or possible miscarriage.
A decreasing serum concentration of hPL is pathognomonic for a malfunction of the placenta that may cause intrauterine growth restriction, an intrauterine death of the fetus, or an imminent miscarriage. Pregnant women experiencing hypertonia also show low serum concentrations of hPL. Because of the short biologi half-life of hPL in serum, the determination of hPL always gives a very accurate picture of the present situation.
Increased serum concentrations of hPL are found in women suffering from diabetes mellitus (DM) and, because of the higher placental mass, in multiple pregnancies. In contrast to estriol, the hPL concentration only depends on the placental mass and not on the fetal function. The simultaneous determination of hPL and estriol can be helpful in the differential evaluation of the placental function.
No single endocrine test has proved to be effective in all cases. Of the current endocrine factors, serum unconjugated estriol would appear to be the best predictor of fetal distress or well-being. However, estriol interpretation is limited because values experience short-term and daily fluctuations. When following high-risk pregnancies, the delivery decision should not be based on a single factor. Rather, the decision to deliver should be based on the estriol values, hPL, and monitoring of the fetal heart rate in response to contractions or stress.
Quantitative (and qualitative) analysis is performed by radial immunodiffusion (RID). ELISA test kits are available and are accurate.
Normal Human Placental Lactogen Levels
Human Placental Lactogen Levels increase as fetal development progress. Levels of Human Placental Lactogen can be detected when approximately at the 20th week of pregnancy. The following is a listing of Normal Human Placental Lactogen Level ranges at the last weeks of pregnency:
Up to 20 weeks: Between 0.05 and 1 mg/L.
Up to 22 weeks: Between 1.5 and 3 mg/L.
Up to 26 weeks: Between 2.5 and 5 mg/L.
Up to 30 weeks: Between 4 and 6.5 mg/L.
Up to 34 weeks: Between 5 and 8 mg/L.
Up to 38 weeks: Between 5.5 and 9.5 mg/L.
Up to 42 weeks: Between 5 and 7 mg/L.
Nuclear Scans Effect on hPL Test Results
Nuclear medicine scans prior to the test affect the test results because a Radioimmunoassay may be used for the determination of Human Placental Lactogen Levels.
Causes of High Human Placental Lactogen Levels
High Human Placental Lactogen Levels can be a result of RH incompatibility between the mother’s blood and the fetus blood.
The following situations are commonly associated with increased placental mass which leads to High Human Placental Lactogen Levels as a result:
- Multiple Pregnancies.
- Placental Site Trophoblastic Tumor.
- Intact Molar Pregnancy.
Causes of Low Human Placental Lactogen Levels
The following diseases are associated with a reduced function of the placenta. As a result Human Placental Lactogen Level is reduced. Pathophysiology of this finding is not clear:
- Placental Insufficiency.
- Hydatidiform Mole.