PS1-16. Umbilical Blood Flow and Fetal Development During Mid Gestation in Singleton, Twin and Triplet Pregnancies in Polypay Ewes.

Abstract Lambs born from multiple (Twins, T and triplets, TR) pregnancies have generally lower birth weights than singletons (S). Previous studies have reported increased VEGF mRNA in periparturient ewes in T pregnancies compared to S and TR. Variation among S, T, and TR gestations is associated with changes in placental angiogenesis and nutrient exchange. Our goal was to characterize umbilical blood flow (UBF) and fetal development in S, T and TR pregnancies during mid-gestation. We hypothesized that multiples would have reduced average UBF per lamb. Thirty four multiparous ewes were divided by fetal number (FN) into three groups: S (n = 11), T (n = 10) and TR (n = 13). Umbilical blood flow, fetal, and placental measurements were collected via ultrasonography every 10 days from day 50 to 110 of gestation. Lamb weights (LW) were recorded at birth and 24h, placentas were collected. Data were analyzed by FN using the MIXED procedure of SAS. There was a significant (P = 0.05) FN × day interaction for UBF with T having greater UBF (343 ± 7.39 ml/min) on day 110 compared to S and TR, which were similar between them (P = 0.98; 317.43 vs 317.59 ± 7.39 ml/min, respectively). There was a FN × day interaction (P < 0.01) for fetal abdominal distance (AD), with T having greater (P ≤ 0.05; 7.08 ± 0.12 cm) AD on day 110 compared to S and TR, which were similar between them (P = 0.06; 6.37 and 6.67 ± 0.12 cm, respectively). There were no significant FN by day interactions (P ≥ 0.26) for placentome length, width, fetal biparietal distance, and pulsatility or resistance indexes. At birth and 24h LW differed (P < 0.01). Singletons were heavier than T and TR, and T were heavier than TR (Birth: 6.29 vs 5.40 vs 4.33 ± 0.30 kg, respectively; 24h: 6.47 vs 5.63 vs 4.36 ± 0.25 kg, respectively). Twins and TR had more (P < 0.01) cotyledons than S and were similar (P = 0.57) between them (101.6 and 105.92 vs 76.4 ± 5.57, respectively). Twins and TR had greater (P < 0.01) total cotyledon weights compared to S and were similar (P = 0.19) between them (266.5 and 307.0 vs 198.7 ± 22.53 g, respectively). Singletons had more (P < 0.01) cotyledons per total LW, than TR, with T being similar (P ≥ 0.11) to both (10.97 vs 8.22 and 9.4 ± 0.66 cotyledons/kg, respectively). Placental expulsion time tended (P = 0.07) to differ with TR being increased (P = 0.02) compared to T, while S was intermediate (3.38 vs 2.43 and 2.97 ± 0.30 hrs, respectively). There was no difference (P = 0.70) in placental efficiency. Our results suggest that UBF does not differ during mid gestation between S and TR. Twins might have a hemodynamic advantage during late mid-gestation, however this does not translate into similar lamb or placental weights.