Pregnancy Due Dates Calculating Your Baby Due Date Without Driving Yourself Crazy
“When am I due? ” is one of the first questions most women ask after they net out they’re pregnant. The answer to this question is not nearly as simple as most people think. For one thing, not all human beings are the same. The range of normal human gestation spans from approximately 38 to 42 weeks. The common knowledge that a pregnancy lasts 9 months is fraught with potential misunderstanding and is fertile for misinterpretation.
Your doctor or midwife has studied the science of the issue. She/he knows that a normal, healthy human pregnancy lasts on average about 280 days, or 40 weeks…….when measured from the first day of the last period. This assumes that a menstrual cycle is about 28 days. In an average 28-day menstrual cycle, a woman usually ovulates around Day 14, or the middle of the cycle; that’s the end of menstrual week #2. Midwives and doctors count these 2 weeks in the gestation period. With this reckoning a woman was already pregnant 2 weeks before she conceived! They count from the beginning of the last menstrual cycle, NOT when that egg was fertilized. That’s just the way it is. So, your midwife or doctor thinks and acts in weeks, not months; and don’t try to divide their weeks by 4 to get the popular opinion of “how many months am I? ” Calendar months are longer than 28-day menstrual cycles, and the length of the months also varies. We are not talking same language here.
Anyway you look at it, for most pregnant women, a pregnancy seems to lasts too long, especially in the last few weeks. It’s important to understand that a due date is an average. The date given for a due date answers the following question: “If 100 women all conceived on the same day, what would the average birthday of their babies be? ” The answer to that question would be a due date based on an average 40 week gestation (remember: we’re talking 40 weeks from the first day of the last period until the birth of the baby).
The reality of human gestation is such that a healthy, full-term pregnancy may last from 38 to 42 weeks. Babies born on or after 38 weeks are usually not premature, and babies born on or before 42 weeks are usually not postmature. So, what most people would like to fill is a due date is really a due period. This due period is about 40 weeks, plus or minus 2 weeks, beginning from the first day of the cycle which prepared the egg that was fertilized. Woman who feel that they are overdue when they go beyond 40 weeks often put pressure on themselves and their clinicians in this period to intervene in what is usually a normal process.
If midwives and doctors used the “due period” belief instead of the due date, and told women that they would have their babies before the end of the 42nd week, we’d all be better off. Since healthy, full-term babies are born between 38 and 42 weeks with clustering around the 40-week “due date”, only half of all babies are actually born on or before their due date, the rest are born after the 40-week due date. That’s a lot of disappointed people when everyone was shooting for the “due date”.
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Filed under ovulation calendar by on Jan 29th, 2012. 