by S Langford

Created on: July 28, 2008

The first weeks of pregnancy involve some major changes taking place in a woman's body. Some women know they are pregnant this early but for many the positive results might not be confirmed for another several weeks. Before discussing some general expectations for the first four weeks it is necessary to examine how the pregnancy time line is determined. How exactly do you determine if you're four weeks pregnant?

In the United States pregnancy is dated by the first date of your last menstrual period. Your doctor will ask for this information during your first prenatal visit and in order to date the pregnancy it is important that you have an accurate idea of the first day your last period started. The result of this is that the 40 week pregnancy is dated from the beginning of your last cycle - not from the moment you actually get pregnant. A typical cycle is based on a 28-day average from the beginning of one menstrual period to the beginning of the next. Most women ovulate about half way through the cycle so fertilization would occur about two weeks after a menstrual period (these are generic formulas but of course every woman is different so this can vary).

What all this means for pregnancy is that by this time line when you reach your fourth week of pregnancy you have actually only been pregnant for two weeks! This can be a little confusing but consider the reasoning for it. It used to be difficult to determine exactly when a woman was ovulating and unless the woman is specifically testing for it, finding out this date can still be a challenge. Most women remember the first day of their last period so it is easier for doctors to estimate the age of a pregnancy based on this information. In some other countries they do not date pregnancies by the first date of the last menstrual period anymore but for our purposes we will assume that pregnancy begins at the beginning of the cycle.

What can you expect for the first four weeks?
Well, weeks one and two you are not yet pregnant so everything should proceed as it always has. During the second two weeks the egg becomes fertilized and travels to the uterus where it implants. Once implantation has occurred a woman's body will start to produce hCG (human chorionic gonadotropin) which is the hormone responsible for the dramatic physical changes that will start soon as well as the culprit that turns that home pregnancy test positive.

Of course, every woman experiences pregnancy differently but here are some of the general

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