Identification

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  Within the process of conception to birth, the blastocyst appears in the first week of conception. Once a woman's egg is fertilized, it travels through the Fallopian tube to the uterus. During this time, the fertilized egg divides into two groups of cells. One group of cells combines to form what will be the embryo, while the second group becomes the outer membrane, or shell for the embryo. This formation is the blastocyst. Its appearance marks the second stage of embryo development.
  
  

Embryo Transport

• The blastocyst is moved through the Fallopian tube by hair-like structures called cilia that work to brush it along. Its movement through this tube is precisely timed to ensure that the blastocyst implants itself within the uterus under the perfect set of conditions. The ability of the embryo to be moved by the cilia, and its ability to grab onto the uterian wall, is dependent on the health of the blastocyst. Any chemical alterations made at this time can adversely affect the success of this process. Nicotine is one of those chemicals, and is so labeled as a developmental toxin when present during fetal development.
  
  

Hormonal Processes

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  As the blastocyst moves through the Fallopian tube, a number of hormone secretions take place. The two hormones released at this time are estrogen and progesterone. The balance between these two hormones determines the rate at which the egg moves through the tube, and its ability to implant itself in the uterus. Ongoing nicotine use is associated with a reduction in estrogen levels. When conception takes place, this lack of available estrogen can have adverse effects on the Fallopian tube's ability to move the egg through, as well as the egg's ability to respond to the tube's movements.
  
  

Ectopic Pregnancy

• Women who smoke might be three times more likely to have an ectopic pregnancy than those who don't smoke, according to emedicine.com. An ectopic pregnancy occurs when the egg attempts to implant itself within the Fallopian tubes instead of inside the uterus. As a result of nicotine, the blastocyst's surface might become sticky, and slow the egg's movement through the tube. Or it might not be sticky enough, to the point where it doesn't adhere at all.
  
  

Embryo Implantation

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  While the blastocyst is making its way to the uterus, the uterus is undergoing physical changes in preparation for the gestation process. Gestation begins once the egg implants itself in the uterus. To prepare for the egg's arrival, the lining in the uterus begins to thicken. This lining is known as the endometrium. Once the egg implants itself, nutrients from the mother will flow through this lining into the placenta and provide nourishment for the developing fetus.
  
  

Birth Complications

• One of the effects of ongoing nicotine use is a less-than-viable uterine lining. The thickness of the endometrium, the health of its cell receptors and its ability to grab onto the embryo are all affected by nicotine's presence in the mother's system. As a result, the likelihood that a fetus will miscarry, be born premature, or have a low birth-weight increases due to the lining's inability to transfer needed nutrients to the embryo.