胎盘发育不充分是造成胎儿死亡和降低妊娠35天后胎儿生长的一个主要原因。妊娠第22-42天的胎盘包括邻近胎儿的中央血管胎盘、分布在胎儿两侧的血管较少的胎盘、坏死胎盘。本研究的目的是全面评估后备母猪早期妊娠过程中子宫-胎盘的发育特性，及决定造成胎儿发育不良和死亡的时间起点和生理变化。25头后备母猪在第一个发情期的24小时后人工授精，分别于妊娠的第22、27、32、37、42天屠宰。
所有妊娠天数屠宰得到的窝仔数相似，均为12.1 ± 3.4。随着妊娠的继续，胎儿、胎盘也随之变重。最大的胎盘增重发现在妊娠第37至42天。低血管分布胎盘直到妊娠第27天都没有出现可测量的折叠构型。坏死胎盘在妊娠第27天消失。妊娠第32至42天子宫内没有被胎儿占据的地方形成折叠，且伴随着子宫内膜上皮细胞的大小和形态的变化。妊娠27至32天，胎儿生长、胎盘重量的变化不大；但是母—胎界面发生了显著变化，表明猪胎盘在早期妊娠中发生了动态的变化。
本项研究确定了与胎儿生长、及可能影响胎儿生长和胎儿存活的胎盘上折叠构型的相关胎盘发育的时间起点。
Uterine and placenta characteristics during early vascular development in the pig
Insufficient placenta development is one of the primary causes of fetal death and reduced fetal growth after 35 days of gestation. Between day 22 and 42 the placenta consists of a central highly vascular placenta （HVP）， adjacent to the fetus, a less vascular placenta （LVP）， on either side of the fetus, and necrotic tips （NT）。 The objective of this study was to comprehensively evaluate uterine–placenta characteristics during early gestation in the gilt and determine time points and physiological changes. Gilts （n = 25） were artificially inseminated at first detection of estrus （day 0） and 24 h later, and harvested at 22, 27, 32, 37 or 42 days of gestation.
Litter size, 12.1 ± 3.4, was similar for all days of gestation. Fetal and placenta weight increased with day of gestation. The greatest increase in placenta weight occurred between 37 and 42 days of gestation. The LVP zones had no measurable fold formation until day 27. Necrotic tips became apparent after 27 days of gestation. Unoccupied areas of the uterus developed folds with changes in endometrial cell size and morphology from day 32 to 42 of gestation. Limited changes occurred in either fetal growth or placenta weight from day 27 through 32 of gestation; however, significant morphological changes occur at the maternal–fetal interface, demonstrating the dynamic architecture of the developing porcine placenta during early gestation.
This work establishes fundamental time points in placenta development corresponding to fetal growth and microfold formation that may influence fetal growth and impact fetal survival.
