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Volume 355:98 July 6, 2006 Number 1
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The Biology of Human Sex Differences

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by Federman, D. D.
-PubMed Citation
To the Editor: In the discussion of biologic differences between male and female fertility (April 6 issue),1 Federman states that women are fertile for only 12 hours each month. Although the egg is viable for 12 hours or less, the window of fertility in women is approximately five to six days in each menstrual cycle,2,3,4 depending on the presence of estrogenic cervical mucus that maximizes the storage, survival, and transport of sperm until ovulation.4,5


Joseph B. Stanford, M.D., M.S.P.H.
University of Utah
Salt Lake City, UT 84108
jstanford@dfpm.utah.edu

  1. Federman DD. The biology of human sex differences. N Engl J Med 2006;354:1507-1514. [Free Full Text]
  2. Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation -- effects on the probability of conception, survival of the pregnancy, and sex of the baby. N Engl J Med 1995;333:1517-1521. [Free Full Text]
  3. Colombo B, Masarotto G. Daily fecundability: first results from a new data base. Demogr Res 2000;3:39-39.
  4. Stanford JB, White GL, Hatasaka H. Timing intercourse to achieve pregnancy: current evidence. Obstet Gynecol 2002;100:1333-1341. [CrossRef][Web of Science][Medline]
  5. Bigelow JL, Dunson DB, Stanford JB, Ecochard R, Gnoth C, Colombo B. Mucus observations in the fertile window: a better predictor of conception than timing of intercourse. Hum Reprod 2004;19:889-892. [Free Full Text]
 
Dr. Federman replies: Stanford rightly calls attention to the elegant estrogen-dominated events . . . [Full Text of this Article]



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