Find Out When Your Baby is Due

There's More Than One Way to Determine Pregnancy Dates

Aug 26, 2009 Mary Earhart

Accurate due dates impact pregnancy care. They should take into account many factors so that intervention can be based on a woman's individual needs.

You can do it the way doctors do: Start with the first day of your last period, add seven days and one year, then subtract three months. This gives you an estimated delivery date with a margin of two weeks either way. In other words, you have a month of possible delivery dates.

Getting Closer

If you know your date of conception (many women are intuitive about it, some have truck driver husbands who are only home once in a while) you can narrow it down more. Count 266 days from that date. Your estimated date of delivery will be within six days before or after that date. You now have twelve days of possible delivery dates.

Another method of calculating a due date takes into consideration how many babies you've had and how long your cycles are. It is named Woods after the midwife who invented it.

Here is the formula: Add one year to the first day of the last menstrual period and subtract 74 days if it is your first baby; subtract 78 days if you have had a baby before.

Next, add or subtract the number of days your cycle (from first day to first day) differs from 28. If your cycle is 21 days long, for example, you would subtract seven days.

That's a bit more complicated but is probably more accurate. Of course it won't work if you have irregular cycles or don't know when your last period started. You can also be confused by a light short period that occurs during the first month of some pregnancies.

Other Indicators

Gestation is measured in weeks since the first day of the last period. You didn't conceive until 10 to 14 days past that, but those days are counted as part of the pregnancy. Also, gestation is expressed in completed weeks, so at the end of your fourth week, you are four weeks. Pregnancy tests will be positive soon after that (your first missed period). Pregnancy generally lasts 40 weeks, with 38 to 42 weeks considered term.

If you don't have any dates, pay attention to the first time you feel movement. The fetus actually starts exercising as early as 10 weeks but moms don't feel it until 15 (if she knows what she's looking for) or 16 (first time moms) weeks.

Another marker your doctor or midwife might use is the height of your fundus (top of the uterus) from the edge of your pubic bone measured in centimeters. At 20 weeks it should be level with your belly button when you lie down. Large babies and twins will be higher.

Ultrasounds can be fairly accurate if done in the first 12 weeks when stages of development can be observed. After that, they are estimates based on averages dependent on measuring long bones and head circumference.

Considerations

A combination of factors gives the most accurate results. It is wise even to take into account dreams, feelings, or thoughts the mother had near her conception date. Once you have a reasonable estimate that sounds right to you, stick with it.

The copyright of the article Find Out When Your Baby is Due in Pregnancy & Childbirth is owned by Mary Earhart. Permission to republish Find Out When Your Baby is Due in print or online must be granted by the author in writing.

A Baby Shower

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