Problem: How does the placental transport of immunoglobulin G (IgG) vary with gestational age?
Method of study: MEDLINE was searched for the appearance of "pregnancy" and "IgG" in the title or abstract from 1966 up to 1995. All publications were reviewed for any kind of IgG data from the fetus and the mother and "known" gestational age. In total, 96 publications from the MEDLINE search fulfilled the search criteria. Seven of ninety-six publications contained IgG and gestational age data from the fetus and/or the mother. Five other publications that fulfilled the same criteria were also available and were also included.
Results: Fetal serum IgG concentrations were found to increase with gestational age according to the formula: fetal IgG = 13.564 - 1.094 x gestational age (GA) + 0.026 x GA2 (R2 = 0.877). The fetomaternal (f/m) ratio was also found to increase with gestational age according to the formula: f/m IgG = 0.399 - 0.059 x GA + 0.003 x GA2 - 2.065 x 10(-5) x GA3 (R2 = 0.831).
Conclusions: The fetal IgG concentrations exceed maternal IgG concentrations after the 35th week of pregnancy. The fetal IgG concentrations are extremely low in the beginning of pregnancy, they exceed 2.5 g/L at > 25 pregnancy weeks, and they reach 5 g/L at pregnancy week 30.