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Relationship of fetal growth to duration of heat stress in an ovine model of placental insufficiency.

Abstract：

OBJECTIVE:Intrauterine growth restriction in an ovine model occurs after exposure to environmental heat stress for 80 days beginning at 35 days' gestation. Our objective was to determine whether intrauterine growth restriction is reversible on removal of the heat stress after only 55 days of exposure; that is, does a brief exposure at a critical point of development suffice? STUDY DESIGN:Five pregnant ewes were exposed to heat stress beginning at 35 days' gestation and were removed after 55 days of exposure. Five ewes in a control group were studied as contemporaneous controls and added to data from 37 ewes in a control group previously studied. Serial fetal biometric ultrasonographic measurements (biparietal diameter, abdominal circumference, femur length, and tibia length) were obtained beginning at 50 days' gestation. Growth curves were calculated for each parameter, and comparisons were made between fetuses in the group exposed to heat stress for 55 days and 42 fetuses in the control group and 4 fetuses from a previous study that were exposed to heat for 80 days. Regression lines, 95% confidence intervals, and slopes were determined for each study group. RESULTS:Both the 55-day and the 80-day heat exposure groups showed a significant reduction in fetal and placental weights compared with the control group. Animals in the 80-day group had significantly lower fetal and placental weights than the animals in the 55-day group (P <.05). Indexes of somatic growth (abdominal circumference, femur length, and tibia length) for the control group were significantly greater than those of either the 55-day group or the 80-day group (P <.001). Asymmetric growth restriction was evident in both heat groups by a biparietal diameter/abdominal circumference ratio that was significantly higher than in the control group (P <.004 for the 55-day group and P <.001 for the 80-day group). The slopes for somatic parameters (abdominal circumference, femur length, and tibia length) versus time became significantly different between the control and 55-day groups at 77, 101, and 80 days' gestation, respectively. The 55-day group had abdominal circumference and femur length measurements that were significantly greater than those in the 80-day group. CONCLUSION:The fetuses in the 55-day and 80-day groups reflect a pattern of asymmetric intrauterine growth restriction. Our findings suggest that the initial insult affecting fetal and placental growth occurs early in gestation, but removal of fetuses after only 55 days of exposure significantly reduces the degree of fetal growth restriction compared with that found in those fetuses exposed for 80 days.

journal_name

Am J Obstet Gynecol

journal_title

American journal of obstetrics and gynecology

authors

Galan HL,Hussey MJ,Barbera A,Ferrazzi E,Chung M,Hobbins JC,Battaglia FC

doi

10.1016/s0002-9378(99)70629-0

subject

Has Abstract

pub_date

1999-05-01 00:00:00

pages

1278-82

issue

eissn

0002-9378

issn

1097-6868

pii

S0002-9378(99)70629-0

journal_volume

180

pub_type

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Relationship of fetal growth to duration of heat stress in an ovine model of placental insufficiency.