Editing Intrauterine growth restriction (section)

==Animals==
In sheep, intrauterine growth restriction can be caused by heat stress in early to mid pregnancy.  The effect is attributed to reduced placental development causing reduced fetal growth.<ref name=Vatnick1991>{{cite journal | vauthors = Vatnick I, Ignotz G, McBride BW, Bell AW | title = Effect of heat stress on ovine placental growth in early pregnancy | journal = Journal of Developmental Physiology | volume = 16 | issue = 3 | pages = 163–6 | date = September 1991 | pmid = 1797923 }}</ref><ref name=Bell1989>{{cite journal |author1=Bell A. W. |title=Chronic Heat Stress and Prenatal Development in Sheep: I. Conceptus Growth and Maternal Plasma Hormones and Metabolites |journal=Journal of Animal Science |author2=McBride B. W. |author3=Slepetis R. |author4=Early R. J. |author5=Currie W. B. | year = 1989 | volume = 67 | issue = 12| pages = 3289–3299 | doi=10.2527/jas1989.67123289x|pmid=2613577 |s2cid=9440955 }}</ref><ref name=Regnault1999>{{cite journal | vauthors = Regnault TR, Orbus RJ, Battaglia FC, Wilkening RB, Anthony RV | title = Altered arterial concentrations of placental hormones during maximal placental growth in a model of placental insufficiency | journal = The Journal of Endocrinology | volume = 162 | issue = 3 | pages = 433–42 | date = September 1999 | pmid = 10467235 | doi = 10.1677/joe.0.1620433 | doi-access = free }}</ref>  Hormonal effects appear implicated in the reduced placental development.<ref name=Regnault1999/> Although early reduction of placental development is not accompanied by concurrent reduction of fetal growth;<ref name=Vatnick1991/> it tends to limit fetal growth later in gestation.  Normally, ovine placental mass increases until about day 70 of gestation,<ref name="pmid8710803">{{cite journal | vauthors = Ehrhardt RA, Bell AW | title = Growth and metabolism of the ovine placenta during mid-gestation | journal = Placenta | volume = 16 | issue = 8 | pages = 727–41 | date = December 1995 | pmid = 8710803 | doi = 10.1016/0143-4004(95)90016-0| doi-access = free }}</ref>  but high demand on the placenta for fetal growth occurs later.  (For example, research results suggest that a normal average singleton Suffolk x Targhee sheep fetus has a mass of about 0.15&nbsp;kg at day 70, and growth rates of about 31 g/day at day 80, 129 g/day at day 120 and 199 g/day at day 140 of gestation, reaching a mass of about 6.21&nbsp;kg at day 140, a few days before parturition.<ref name="pmid4819552">{{cite journal | vauthors = Rattray PV, Garrett WN, East NE, Hinman N | title = Growth, development and composition of the ovine conceptus and mammary gland during pregnancy | journal = Journal of Animal Science | volume = 38 | issue = 3 | pages = 613–26 | date = March 1974 | pmid = 4819552 | doi = 10.2527/jas1974.383613x | doi-access = free }}</ref>)

In adolescent ewes (i.e. ewe hoggets), overfeeding during pregnancy can also cause intrauterine growth restriction, by altering nutrient partitioning between dam and conceptus.<ref>{{cite journal | author = Wallace J. M. | year = 2000 | title = Nutrient partitioning during pregnancy: adverse gestational outcome in overnourished adolescent dams | journal = Proc. Nutr. Soc. | volume = 59 | issue = 1| pages = 107–117 | doi=10.1017/s0029665100000136| pmid = 10828180 | doi-access = free }}</ref><ref name=Wallace2005>{{cite journal |author1=Wallace J. M. |author2=Regnault T. R. H. |author3=Limesand S. W. |author4=Hay Jr. |author5=Anthony R. V. | year = 2005 | title = Investigating the causes of low birth weights in contrasting ovine paradigms | journal = J. Physiol. | volume = 565 | issue = Pt 1| pages = 19–26 | doi=10.1113/jphysiol.2004.082032|pmid=15774527 |pmc=1464509 }}</ref>  Fetal growth restriction in adolescent ewes overnourished during early to mid pregnancy is not avoided by switching to lower nutrient intake after day 90 of gestation; whereas such switching at day 50 does result in greater placental growth and enhanced pregnancy outcome.<ref name=Wallace2005/>  Practical implications include the importance of estimating a threshold for "overnutrition" in management of pregnant ewe hoggets.  In a study of Romney and Coopworth ewe hoggets bred to Perendale rams, feeding to approximate a conceptus-free live mass gain of 0.15&nbsp;kg/day (i.e. in addition to conceptus mass), commencing 13 days after the midpoint of a synchronized breeding period, yielded no reduction in lamb birth mass, where compared with feeding treatments yielding conceptus-free live mass gains of about 0 and 0.075&nbsp;kg/day.<ref name="MorrisKenyon2010">{{cite journal|vauthors =Morris ST, Kenyon PR, West DM |title=Effect of hogget nutrition in pregnancy on lamb birthweight and survival to weaning|journal=New Zealand Journal of Agricultural Research|volume=48|issue=2|year=2010|pages=165–175|issn=0028-8233|doi=10.1080/00288233.2005.9513647|doi-access=free}}</ref>
In both of the above models of IUGR in sheep, the absolute magnitude of uterine blood flow is reduced.<ref name=Wallace2005/>  Evidence of substantial reduction of placental glucose transport capacity has been observed in pregnant ewes that had been heat-stressed during placental development.<ref name="pmid3559063">{{cite journal | vauthors = Bell AW, Wilkening RB, Meschia G | title = Some aspects of placental function in chronically heat-stressed ewes | journal = Journal of Developmental Physiology | volume = 9 | issue = 1 | pages = 17–29 | date = February 1987 | pmid = 3559063}}</ref><ref name="pmid1415644">{{cite journal | vauthors = Thureen PJ, Trembler KA, Meschia G, Makowski EL, Wilkening RB | title = Placental glucose transport in heat-induced fetal growth retardation | journal = The American Journal of Physiology | volume = 263 | issue = 3 Pt 2 | pages = R578–85 | date = September 1992 | pmid = 1415644 | doi = 10.1152/ajpregu.1992.263.3.R578 }}</ref>