Effects of twin pregnancy and periconceptional undernutrition on maternal metabolism, fetal growth and glucose-insulin axis function in ovine pregnancy

Abstract

Although twins have lower birthweights than singletons, they may not experience the increased disease risk in adulthood reportedly associated with low birthweight. In contrast, another periconceptional event, maternal undernutrition, does not reduce birthweight but does affect fetal and postnatal physiology in sheep. We therefore studied maternal and fetal metabolism, growth and glucose-insulin axis function in late gestation in twin and singleton sheep pregnancies, either undernourished from 60 days before until 30 days after conception or fed ad libitum. We found that twin-bearing ewes had decreased maternal food intake in late gestation and lower maternal and fetal plasma glucose and insulin levels. Twin fetuses had fewer everted placentomes, grew slower in late gestation, and had a greater insulin response to a glucose challenge, but lesser response to arginine. In contrast, periconceptional undernutrition led to increased maternal food intake and a more rapid fall in maternal glucose levels in response to fasting. Periconceptional undernutrition increased the number of everted placentomes, and abolished the difference in insulin responses to glucose between twins and singletons. Thus, the physiology of twin pregnancy is quite different from that of singleton pregnancy, and is probably determined by a combination of factors acting in both early and late gestation. The inconsistency of the relationships between low birthweight and postnatal disease risk of twins may lie in their very different fetal development. These data suggest that twin pregnancy may be another paradigm of developmental programming, and indicate that twins and singletons must be examined separately in any study of fetal or postnatal physiology.

Figure 1. Timeline of experimental protocol

PCUN, periconceptional undernutrition; N, well-nourished throughout.

Figure 2. Fetal growth curves

A, fetal growth curves in singleton and twins. •, singleton N; ○, singleton PCUN; ▪, twin N; □, twin PCUN. PCUN, periconceptional undernutrition. Symbols represent effect on growth rate. ††P < 0.01 for twin effect. B, fetal growth curves in twins divided into heavy and light twins. Large filled triangle, twin heavy N; small filled triangle, twin light N; large open triangle, twin heavy PCUN; small open triangle, twin light PCUN. PCUN, periconceptional undernutrition. Symbols represent effect on growth rate. ∫∫P < 0.01, ∫P < 0.05 for heavy/light effect. ∫P < 0.05 for heavy/light × nutrition interaction.

Figure 3. Fetal glucose (A) and insulin (B) responses to an intravenous glucose tolerance test; arginine (C) and insulin (D) responses to an intravenous arginine challenge

Areas under the curve shown as inset histograms. PCUN, periconceptional undernutrition. See text for details of nutritional groups. •, singleton N (SN) (n = 15); ○, singleton PCUN (SU) (n = 13); ▪, twin N (TN) (n = 26); □, twin PCUN (TU) (n = 30). Data are mean ±s.e.m.†P < 0.05 for twin effect; **P < 0.01 for nutrition effect; #P < 0.05 for twin–nutrition interaction.

Figure 4. Maternal glucose (A) and insulin (B), and fetal glucose (C) and insulin (D) levels during fasting and refeeding

Fasting period (days 121–124) indicated by filled bar, glucose infusion indicated by open bar. Data are mean ±s.e.m. PCUN, periconceptional undernutrition. See text for details of nutritional groups. •, singleton N (n = 10); ○, singleton PCUN (n = 12); ▪, twin N (n = 12); □, twin PCUN (n = 10). §P < 0.05; §§P < 0.01 for twin × time interaction; #P < 0.05; ##P < 0.01 for twin × nutrition interaction; ‡P < 0.05; ‡‡P < 0.01 for twin × nutrition × time interaction.