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Pregnancy at 3 Weeks

In the third week of pregnancy, the expectant mother does not even know she is pregnant and will most likely not be noticing any changes in her body. Since a pregnancy actually begins on the first day of a woman’s last menstrual period, conception does not occur until the third week of pregnancy. During the third week of pregnancy, fertilization occurs and a baby begins to form.


Fertilization occurs when a sperm and egg meet in the fallopian tubes. The fertilized egg will continue to travel down the fallopian tubes until it implants in the uterus, which will be its home until delivery. The thick lining that has been forming as part of a normal menstrual cycle will help create an environment that is just right for the fertilized egg to implant and start to develop.

Implantation Bleeding

Some women may experience slight spotting when implantation occurs. This implantation bleeding is very light but is too early to be mistaken for the start of a woman’s period. Not all women notice or experience implantation bleeding. Women who have experienced implantation bleeding during previous pregnancies may know what to look for and may be more likely to notice it if it happens in future pregnancies.

Gender Determination

The gender of an unborn baby is determined at the moment of conception. A baby receives half of a mother’s DNA and half of a father’s DNA. Sex chromosomes in the father’s sperm determine a baby’s gender, although the sex will not be clear on an ultrasound until much later.

Early Signs of Pregnancy

Most women experience no pregnancy symptoms until they are six or seven weeks pregnant. Some women notice fatigue, breast tenderness, bleeding gums, and minor food aversions. During the third week of pregnancy, a woman is not aware that she is expecting, and most symptoms go unnoticed or are attributed to other causes.

Fetal Development at Three Weeks

While an new mother may not be aware that she is expecting during the third week of pregnancy, the unborn baby is going through a period of rapid development. At this stage of pregnancy, the baby is called a zygote. After implantation, the fertilized egg will split in half. One half will become the fetus and the other half will become the placenta that will help nourish the baby until birth. The implanted zygote will begin to produce HCG hormone. This is the hormone that home pregnancy tests look for and will help confirm a pregnancy during the fourth or fifth week of pregnancy.

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