Dating pregnancy late ovulation
When we are still pregnant after that magical date, we call ourselves "overdue" and the days seem to drag on like years.
The problem with this belief about the 40 week EDD is that it is not based in fact.
For multiparas, mothers who had previously given birth, the average gestational length was 283 days or 40 weeks 3 days.
To easily calculate this EDD formula, a nullipara would take the LMP, subtract 3 months, then add 15 days.
Not all women have a 28 day cycle; some are longer, some are shorter, and even those with a 28 day cycle do not always ovulate right on day 14.
If a woman has a cycle which is significantly longer than 28 days and the baby is forced out too soon because her due date is calculated according to her LMP (last menstrual period), this can result in a premature baby with potential health problems at birth.
The "due date" we are given at that first prenatal visit is based upon that 40 weeks, and we look forward to it with great anticipation.Multiparas start with LMP, subtract 3 months and add 10 days.In fact, if left alone, 50-80% of mothers will gestate beyond 40 weeks.Variants in cycle length Aside from the gross miscalculation of the lunar due date, there is another common problem associated with formulating a woman's EDD: most methods of calculating gestational length are based upon a 28 day cycle.
The inaccuracy of ultrasound First trimester: 7 days 14 - 20 weeks: 10 days 21 - 30 weeks: 14 days 31 - 42 weeks: 21 days Calculating an accurate EDD Recent research offers a more accurate method of approximating gestational length. undertook a study to calculate the average length of uncomplicated human pregnancy.They found that for first time mothers (nulliparas) pregnancy lasted an average of 288 days (41 weeks 1 day).