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For more information on twin biology, refer to Twin Services' Parenting Education Handout #125, "Twin Beginnings".
Geoffrey Machin is the fetal pathologist for the Northern California region of Kaiser Permanente Medical Centers. His book, Biology and Pathology of Twins, is forthcoming in July 1997.
Reprinted with permission from Twin Services Reporter, Spring 1997. This article may be printed out for personal use but may not be reproduced in any other manner, including electronic, without prior written consent from Twin Services. For more information, email us at email@example.com or call us at 510-524-0863.