Normal ALT Levels During Pregnancy
During pregnancy, normal ALT levels are 6-32 IU/L in the first trimester, with values remaining at or below 40 IU/L throughout gestation, which is lower than or similar to non-pregnant reference ranges. 1
Trimester-Specific Reference Ranges
The most authoritative guidance comes from the 2023 EASL Clinical Practice Guidelines, which provides specific normal ranges for each trimester 1:
The 2023 EASL guidelines note that ALT values are not separately defined for second and third trimesters in their reference table, but AST values (which typically parallel ALT) are listed as 11-29 IU/L in the second trimester and 11-30 IU/L in the third trimester 1. This suggests ALT remains within similar ranges throughout pregnancy.
Key Physiological Changes
ALT levels during normal pregnancy typically remain within or slightly below non-pregnant reference ranges, with no significant elevation expected. 2 A prospective study of 103 pregnant women with matched controls found that serum ALT activity was only slightly higher in second-trimester pregnant women (8.2 ± 5.8 vs. 6.8 ± 4.5 IU/L), though all values remained within normal limits 2.
The AASLD 2021 guidance confirms that in healthy pregnancy, most liver tests remain normal, with the notable exception of alkaline phosphatase which increases due to placental production 1.
Clinical Significance of Elevated ALT
Any ALT elevation above 40 IU/L warrants investigation for pregnancy-specific liver diseases or underlying hepatic pathology. 1
When ALT is elevated during pregnancy, consider these differential diagnoses based on severity 1:
- Mild elevation (2-30× ULN): Intrahepatic cholestasis of pregnancy (ICP), where ALT elevations of 2-30 times the upper limit of normal may occur 1
- Moderate elevation (300-1,000 U/L): Acute fatty liver of pregnancy (AFLP) 1
- Variable elevation: Hyperemesis gravidarum (rarely >1,000 U/L, typically improves with hydration) 1
- Elevated with other features: HELLP syndrome (hemolysis, elevated liver enzymes, low platelets) 1
Important Clinical Caveats
Elevated ALT in early pregnancy (>95th percentile) is associated with increased risk of gestational diabetes and preeclampsia later in pregnancy. 3 A retrospective cohort study found that women with elevated early ALT had higher rates of gestational diabetes (6.5% vs. 2.1%) and preeclampsia (4.1% vs. 1.0%) compared to those with normal ALT 3.
Recent prevalence data shows that approximately 13% of pregnant women presenting to labor and delivery have ALT ≥25 IU/L, with nearly half of these cases not having had liver tests checked during routine prenatal care 4. This suggests that mild ALT elevations may be more common than previously recognized, though the clinical significance of values between 25-40 IU/L remains unclear 4.
In women with chronic hepatitis B, ALT flares during pregnancy or postpartum are infrequent (3.4% during pregnancy, 4.3% postpartum), typically mild (range 107-513 U/L), and self-limited. 5
Practical Monitoring Approach
For women with suspected or confirmed liver disease in pregnancy, the EASL guidelines recommend 1:
- Baseline measurement of ALT, AST, bilirubin, and bile acids when liver disease is suspected
- Serial monitoring every 2-3 weeks before 32 weeks gestation, then weekly until delivery for conditions like ICP 1
- Postpartum follow-up to ensure ALT normalizes within 3 months of delivery; persistent elevation requires investigation for underlying chronic liver disease 1