Alkaline phosphatase (ALP) is an enzyme found throughout the human body, involved in various biological processes. During pregnancy, ALP levels naturally increase, especially as the pregnancy advances into the third trimester. This physiological rise is a normal adaptation and does not typically signify an underlying health concern.
The Role of Alkaline Phosphatase in the Body
ALP functions broadly in the body by helping to break down proteins and is involved in various metabolic processes, including the transport of phosphates. In non-pregnant individuals, ALP is primarily found in the liver, bones, kidneys, and intestines. The liver and bones are the main contributors to ALP levels in the bloodstream. ALP plays a role in bone development and calcification. In the liver, it is involved in phosphate transport into bile, and in the intestines, it aids phosphate transport into epithelial cells.
Placental Alkaline Phosphatase and Pregnancy
During pregnancy, a specific type of ALP, known as placental alkaline phosphatase (PLAP), is produced. This isoenzyme originates from the placenta, which develops to support the growing fetus. The placenta produces substantial amounts of PLAP, which then enters the mother’s bloodstream. PLAP contributes to the maternal-fetal barrier, the interface separating the mother’s and baby’s blood within the placenta. Its continuous increase throughout gestation indicates a role in feto-maternal metabolism and placental differentiation. This enzyme also regulates phosphate metabolism during pregnancy, supporting placental growth and nutrient transport to the fetus.
Defining Normal Third Trimester Levels
Normal ALP levels in the third trimester of pregnancy are significantly higher than in non-pregnant individuals, often two to four times greater. For instance, while a typical non-pregnant range might be 30-120 U/L, third-trimester levels can range from 38 U/L to 229 U/L. Specific reference ranges vary between different laboratories due to varying equipment and testing methods. Healthcare providers compare a patient’s ALP results to the reference range provided on their individual lab report. This ALP elevation is progressive, starting at the end of the first trimester and continuing to rise, peaking closer to the delivery date.
When Elevated Levels May Indicate a Problem
While a significant rise in ALP is normal during the third trimester, abnormally high levels, exceeding the expected physiological range, can indicate certain conditions. One such condition is intrahepatic cholestasis of pregnancy (ICP), a liver disorder characterized by intense itching, particularly on the palms and soles. In ICP, bile acids accumulate; ALP may be elevated, but other liver function tests like bile acids are more definitive for diagnosis.
Other conditions associated with abnormally high ALP include preeclampsia and HELLP syndrome. Preeclampsia, marked by new-onset high blood pressure and protein in the urine after 20 weeks of gestation, can involve elevated liver enzymes, including ALP. HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet count) is a complication that can arise from preeclampsia. ALP elevation is considered alongside other symptoms and laboratory findings, such as blood pressure readings, platelet counts, and other liver function tests, for diagnosis.