Immunoglobulin G (IgG), Serum
Immunoglobulin G (IgG) is the dominant circulating antibody and the only immunoglobulin class that actively crosses the placenta. During pregnancy, maternal IgG levels gradually decline due to plasma volume expansion and increasing fetal transfer, with the greatest transfer occurring in the third trimester.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| mg/dL | 700 – 1700 | 838 – 1410 | 654 – 1290 | 522 – 1146 |
| g/L | 7 – 17 | 8.38 – 14.1 | 6.54 – 12.9 | 5.22 – 11.46 |
Clinical note: Progressive maternal IgG decline in late pregnancy reflects both hemodilution and active placental transport to establish neonatal passive immunity.
Causes of low IgG in pregnancy
- Physiologic hemodilution of pregnancy
- Placental transfer of IgG to the fetus (especially in the third trimester)
- Primary immunodeficiency (e.g., common variable immunodeficiency)
- Protein loss (nephrotic syndrome, protein-losing enteropathy)
- Chronic corticosteroid use or immunosuppressive therapy
- Malnutrition or malabsorption
- Liver disease with impaired immunoglobulin synthesis
Causes of high IgG in pregnancy
- Chronic inflammation or infection
- Autoimmune disease (e.g., SLE, rheumatoid arthritis)
- Chronic liver disease, especially autoimmune hepatitis
- Monoclonal gammopathy (rare in pregnancy)
- Granulomatous disease (sarcoidosis, tuberculosis)
References
- Lockitch G. Handbook of Diagnostic Biochemistry and Hematology in Normal Pregnancy. CRC Press; 1993.
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Obstet Gynecol. 2009.