Inner Cell Mass

Inner cell mass Uterine epithelium Uterine stroma

Inner cell mass Uterine epithelium Uterine stroma

Inner Cell Mass

Figure 2.10 A. Section of a 107-cell human blastocyst showing inner cell mass and trophoblast cells. B. Schematic representation of a human blastocyst recovered from the uterine cavity at approximately 4.5 days. Blue, inner cell mass or embryoblast; green, trophoblast. C. Schematic representation of a blastocyst at the ninth day of development showing trophoblast cells at the embryonic pole of the blastocyst penetrating the uterine mucosa. The human blastocyst begins to penetrate the uterine mucosa by the sixth day of development.

Figure 2.10 A. Section of a 107-cell human blastocyst showing inner cell mass and trophoblast cells. B. Schematic representation of a human blastocyst recovered from the uterine cavity at approximately 4.5 days. Blue, inner cell mass or embryoblast; green, trophoblast. C. Schematic representation of a blastocyst at the ninth day of development showing trophoblast cells at the embryonic pole of the blastocyst penetrating the uterine mucosa. The human blastocyst begins to penetrate the uterine mucosa by the sixth day of development.

CLINICAL CORRELATES Abnormal Zygotes

The exact number of abnormal zygotes formed is unknown because they are usually lost within 2 to 3 weeks of fertilization, before the woman realizes she is pregnant, and therefore are not detected. Estimates are that as many as 50% of pregnancies end in spontaneous abortion and that half of these losses are a result of chromosomal abnormalities. These abortions are a natural means of screening embryos for defects, reducing the incidence of congenital malformations. Without this phenomenon, approximately 12% instead of 2% to 3% of infants would have birth defects.

With the use of a combination of IVF and polymerase chain reaction (PCR), molecular screening of embryos for genetic defects is being conducted. Single blastomeres from early-stage embryos can be removed and their DNA amplified for analysis. As the Human Genome Project provides more sequencing information and as specific genes are linked to various syndromes, such procedures will become more commonplace.

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Pregnancy Guide

Pregnancy Guide

A Beginner's Guide to Healthy Pregnancy. If you suspect, or know, that you are pregnant, we ho pe you have already visited your doctor. Presuming that you have confirmed your suspicions and that this is your first child, or that you wish to take better care of yourself d uring pregnancy than you did during your other pregnancies; you have come to the right place.

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