Twin conception reduces birth weight and gestation length in sheep, regardless of fetal number in late gestation

Objective: Twins are commonly born both early and small and these factors are associated with adverse long-term health outcomes. The dogma is that constraints of uterine size and placental supply in late gestation are responsible, but there are no data to support this. The periconceptional period is known to be important for fetal development and gestation length. We hypothesised that conception per se as a twin would alter fetal growth and the timing of birth. Methods: Time-mated twin-bearing ewes were randomly assigned to fetal reduction of one twin (reductions; n532) or a sham procedure (twins; n520). Singleton-bearing ewes (singles; n523) also underwent a sham procedure. Fetal reduction was achieved through ultrasound-guided transabdominal injection of 1.5mL 2M KCl into the heart or chest cavity on day 42 of gestation (term5147 d). Gestation lengths, birth weight, and other anthropometric measurements were recorded at, or shortly after, birth. Data were compared by ANOVA with post-hoc correction and are presented as mean (SEM). Results: Gestation length was shorter in twins than singles (147.0 (0.32) vs 148.3 (0.34) d; P,0.05); reductions had intermediate gestation length (147.3 (0.46) d). Birth weight was greatest in singles, intermediate in reductions, and least in twins, each group being statistically different (singles 6.60 (0.16) Kg; reductions 5.82 (0.14) Kg; twins (5.23 (0.12) Kg; all comparisons P,0.0001). Other anthropometric data were similar between reductions and twins, with singles significantly larger than these two groups (P,0.05). These findings are not altered by adjustment for gestation length. Conclusion: Following reduction of twin pregnancies to singletons in early gestation, birthweight and gestation length remain less than in singletons. These are the first experimental data demonstrating that gestation length and birthweight in twin fetuses are determined, at least in part, in early gestation. However, the significantly greater birthweight in reductions compared with twins indicates that there is additional constraint of growth in late gestation. Birth weight and gestation length are therefore influenced by fetal number both at the time of conception and in late gestation. Further studies will determine whether this altered growth has longterm implications for growth and risk of disease

Size at birth and adult fat mass in twin sheep are determined in early gestation

- Reduced size at birth and shorter gestation length are both associated with increased risks of non‐communicable diseases (NCD) in later adult life. - Twins are born both smaller and earlier than singletons and adult twins also are reported to be at increased risk of common NCDs such as diabetes. - The smaller size and shorter gestation length of twins has been presumed to be due to a lack of intrauterine space and/or limitations of placental nutrient supply in late gestation, but there are few data to support this. - We show that size at birth and adult fat mass in twin sheep are determined largely in early gestation. - Knowledge of the mechanisms underlying early pregnancy determination of fetal growth and gestation length in twins are likely to increase understanding of how early pregnancy factors influence lifelong health for offspring from all pregnancies

Effects of periconceptional undernutrition on the initiation of parturition in sheep

In sheep, parturition is initiated by increased fetal hypothalamic-pituitary-adrenal axis ( HPAA) activity leading to PGE(2) and PGF(2alpha) production and a rise in the 17beta-estradiol-progesterone (E-2/P-4) ratio. Uteroplacental PG production can also increase fetal HPAA activity. Periconceptional maternal undernutrition accelerates fetal HPAA maturation resulting in preterm labor. We determined whether preterm labor was preceded by an increase in PG concentrations and E-2/P-4 ratio and whether these increases preceded or followed the corresponding rise in cortisol concentrations. Singleton-bearing ewes were nourished ad libitum (N, n = 9) or undernourished (UN, n = 10) to reduce maternal weight by 15% from - 61 days (d) to + 30 d after mating with ad libitum intake thereafter. Paired maternal and fetal blood samples were collected from 126 d until delivery. Half the UN group delivered prematurely ( > 2 SD below mean gestation for the flock). PG and cortisol concentrations and E-2/P-4 ratio increased before delivery in the same way in both groups. However, the increases occurred 7 - 10 d earlier in UN than in N animals. In both UN and N fetuses cortisol concentrations rose before fetal and maternal PG concentrations and maternal E-2/P-4 ratio. Periconceptional maternal undernutrition induces preterm delivery in sheep by advancing the expected prepartum rise in cortisol and PG concentrations and E-2/P-4 ratio. The rise in fetal cortisol concentration precedes the rise in fetal and maternal PG concentrations and maternal E-2/P-4 ratio, suggesting that the underlying mechanism is likely to be acceleration of fetal HPAA maturation, resulting in initiation of the normal process of parturition

Twin conception in sheep leads to impaired insulin sensitivity and sexually dimorphic adipose tissue and skeletal muscle phenotypes in adulthood

Twins are often born small and early and have increased risk of obesity and diabetes later in life. Twin conception in sheep, regardless of whether the pregnancy continues as twins or is reduced to singleton in early gestation, alters offspring growth trajectory and body composition in young adulthood. We hypothesized that twin conception would result in insulin resistance in adulthood, with insulin-resistant adipose tissue and skeletal muscle phenotypes. At 3 years of age, body weight was not different among singletons, twins, and reductions; females weighed less than males. Singletons were leaner than reductions, with twins intermediate. Twins and reductions had decreased insulin sensitivity compared with singletons (singletons: mean [standard error of the mean]: 4.75 [0.4], twins: 3.34 [0.3], reductions: 3.67 [0.2] mg·I μU-'1·kg-'1·min-'1, P <.01). There were no group differences in adipocyte size, adipose tissue, or circulating tumor necrosis factor α, monocyte chemoattractant protein 1, or interleukin 6 concentrations. In males, omental and subcutaneous adipose SLC2A4 was 1.5- to 2.0-fold greater in twins and reductions than in singletons (P <.01) and SLC2A1 was greater in reductions than in singletons. Skeletal muscle IRS-1 was decreased in male twins but increased in female twins, compared to singletons (P ≤.01), with no effect on reductions in either sex. Skeletal muscle SLC2A4 was decreased in female twins and reductions but elevated in male twins and reductions compared to singletons (P ≤.01). We conclude that adult twin insulin resistance is not due to adipose tissue phenotype, but potentially phenotypic effects in skeletal muscle, and obesity is a result of twin conception per se with its origins in early gestation

Effect of periconceptional undernutrition in sheep on late gestation expression of mRNA and protein from genes involved in fetal adrenal steroidogenesis and placental prostaglandin production

In sheep, maternal periconceptional undernutrition precociously activates fetal hypothalamic-pituitary-adrenal function in a high proportion of animals, resulting in preterm birth. We investigated whether the effects of periconceptional undernutrition were mediated through genes encoding enzymes involved in adrenal steroidogenesis and in placental production and metabolism of steroids and prostaglandins. Singleton-bearing ewes were fed ad libitum (control, N) throughout gestation or undernourished from 60 days before until 30 days after mating. Fetal adrenal and placentome tissues were collected on gestational day 131. Fetal adrenal P450C17 protein expression was significantly increased with undernutrition. Placental prostaglandin endoperoxide synthase-2 expression was not different between groups. In undernourished pregnancies, there were significant positive correlations between fetal plasma adrenocorticotrophic hormone and cortisol concentrations and between fetal plasma adrenocorticotrophic hormone concentrations and placental prostaglandin endoperoxide synthase-2 messenger RNA (mRNA) and protein. These studies suggest that periconceptional undernutrition affects fetal adrenal P450C17, consistent with an elevation in plasma cortisol, and this occurs prior to activation of placental prostaglandin endoperoxide synthase-2 expression at gestational day 131

Mixed linear regression with equi-cross-correlated errors

Generalized Least Squares, parameter-dependent covariance structure, canonical correlation analysis, efficiency comparisons, tests of independence,