It is impossible to be one week pregnant. It is impossible to be two weeks pregnant. In fact, you’re not really pregnant until the third week. Confused?
Pregnancy is 40 weeks long, but that number is counted from the “first day” of your cycle. When you are in the first week of pregnancy, your baby is no more than a hope in your heart (and you’re likely having your period). During the second week, you’re more than likely doing the baby dance and by the end of that week, conception occurs. Fourteen is the magic number! From that day on, you are truly pregnant in the sense that there is an actual baby growing in your womb, but you probably won’t know until week four or later. You will be able to see her heart beating in an ultrasound during week five or six.
Since not all women have 28 day cycles or ovulate on day 14, this method for determining your due date is not always accurate unless you make a few adjustments. If you start the clock 2 weeks before ovulation, whenever that may be, you will be able to calculate how many weeks pregnant you are. But what if you don’t know when you ovulated? These days, your obstetrician can do an early ultrasound to determine the gestational age of your baby based on measurements. During the first part of pregnancy, all babies generally grow at the same rate, making these ultrasounds fairly accurate. I knew exactly what day I ovulated, for example, so I was able to calculate my exact due date. The due date my doctor gave me based on my early ultrasound was only two days later than the date I came up with. My son was born three days before my calculated due date and five days before my “official” due date. That’s pretty accurate, if you ask me!
Another confusing aspect of gestational age terminology is how you express the number of weeks or months. Some books will talk about pregnancy based on how many weeks pregnant you are (how many weeks you have completed), and some will talk about it based on what week of pregnancy you are in. When you are 4 weeks and 2 days pregnant, you are in your fifth week. When you are 22 weeks and 1 day pregnant, you have just begun your 23rd week. When you are 40 weeks and 2 days pregnant, not only are you overdue, but you are in your 41st week. If that weren’t confusing enough, different books or web sites count the months differently. Some count the months based on the date of your due date, counting backwards month to month. For example, if you are due on February 4th of this year, today you would be exactly 8 months pregnant. Other sources, however, count months every four weeks, which makes you 10 months pregnant by the time you give birth, not nine. Well the only month of the year that has 4 weeks is February, and in a leap year, even February is longer than 4 weeks. The average number of weeks in a month is 4.3, and over the course of nine months, that method of counting becomes more and more inaccurate. It drives me nuts, and that is why I count by the date, not the weeks.
So remember, by day 18, you are 2 weeks and 4 days pregnant (unknowingly), you are in week three and you are in your first month. It has been just four days since your baby was conceived and you may be able to detect her presence with a home pregnancy test in about ten days. By the time you see the double line, you will be excited to know that you have already completed your first month of pregnancy (easiest month by far) and you only have 8 to go!