<td><img src="http://cimg2.163.com/health/2006/5/30/2006053015422184818.jpg" border="0" onload="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {}" onmousewheel="return imgzoom(this);" alt="" /></td><td> 在正常情况下,胎儿在子宫内是头朝下的。</td><td><img width="400" height="320" src="http://cimg2.163.com/health/2006/5/30/2006053015432228f72.jpg" border="0" alt="" /></td><td> 某些胎位会造成阴道生产的风险。如,胎盘前置会阻塞胎儿产出的通道,胎盘早剥会严重影响胎儿的氧气及营养的供给等。