Decreased maternal lipolysis in intrauterine growth restriction in the third trimester

Objective: Intrauterine growth restriction (IUGR) is a common complication of pregnancy. There are many possible aetiologic factors of maternal, placental and/or fetal origin. Often there is no known explanation. The aim of this study was to investigate whether a reduction in maternal energy substrate production could be one of the factors involved in IUGR. Design: Measurement of maternal energy substrate production and glucoregulatory hormones in women with growth-restricted fetuses. Settings: University Hospital, Uppsala, Sweden. Population: Ten healthy pregnant women with IUGR were compared with eight recently reported healthy women with normal pregnancies. The women were studied at 35.4 +/- 1.6 weeks of gestation after an overnight fast. Methods: Rates of glycerol and glucose production were analysed by gas chromatography/mass spectrometry following constant-rate infusion of [1,1,2,3,3-H-2(5)]glycerol and [6,6-H-2(2)]glucose. Main outcome measure: Third trimester glycerol and glucose production. Results: Glycerol production, reflecting lipolysis, was lower in the women with IUGR than in those with normal pregnancies, 2.36 +/- 0.58 versus 3.06 +/- 0.66 mu mol kg(-1) minute(-1) (P = 0.033), whereas there was no difference in rate of glucose production (glucose production rate [GPR]), 12.1 +/- 1.5 versus 13.2 +/- 1.5 mu mol kg(-1) minute(-1) (P = 0.23). Plasma glycerol levels were increased in the women with IUGR (P = 0.008). Conclusions: Lipolysis is lower in pregnancies complicated by IUGR as compared with normal pregnancies. Increased lipolysis during pregnancy provides substrate for maternal energy metabolism, which spares glucose for the fetus. A reduced maternal production of energy substrate could be one of several factors underlying IUGR. A lack of relationship between insulin levels and either lipolysis or GPR suggests defective regulation of energy substrate production in this group of pregnant women.