DEVELOPMENTAL HAZARDS OF HUMAN TWINS 147 



cases development is at least measurably retarded. The 

 diminished blood pressure and the lack of turgescence 

 are often followed by definite nutritional disturbances. 

 The kidneys, through lessened functioning, are arrested 

 and as a consequence there is a decrease in the secretion 

 of urine and a corresponding resorption of the amniotic 

 fluid. This may be followed by serious mechanical 

 consequences such as pressure of the fetus against the 

 membranes and consequent adhesions. As a result of 

 these physiological disturbances, intra-uterine death 

 often occurs in one of the twins. Schatz has shown 

 that intra-uterine death in one-egg twins occurs three 

 times as frequently as in two-egg twins. This seems to 

 indicate that a high percentage of the prenatal deaths of 

 one-egg twins is to be attributed to the influences such 

 twins exert upon each other through their intimate 

 vascular interrelations. Probably at least half of the 

 deaths in one-egg twins are due to causes that are inde- 

 pendent of twinning, such as primary death of the heart 

 or twisting of the umbiHcal cord. The remaining deaths 

 are those in which we are especially interested because 

 they are due to conditions pecuHar to one-egg twins: 

 namely, pronounced asymmetry of the placental third 

 circulation and the immediate or secondary consequences 

 of the latter. 



HOW THE DAMAGE IS DONE 



As the result of an anatomical derangement or asym- 

 metry of the vascular system, one of the twins is robbed 

 of the blood supply necessary for its normal nourishment 

 and functioning. The result is a progressive weakening of 

 the heart with an accompanying decrease in size. The 

 pressure of the blood from the stronger opposite twin 



