Time to Do Away
With the Due Date?

Experts Wonder if Pregnancy Due Dates Are Past Their Prime

By Jenette Restivo

B O S T O N, Nov. 30 — The due date. It's one of the precious pieces of information expecting mothers will have about their babies as they carry them for nine months.

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Or is it? In a commentary appearing in December's journal Obstetrics and Gynecology, Dr. Vern Katz, of the Center for Genetics and Maternal Fetal Medicine in Oregon, says that 95 percent of women deliver outside of their due date. So, argues Katz, it's time to lay the term to rest.

The erroneous concept of a due date, Katz maintains, only leads expecting parents to feel frustration and anxiety about the health of their baby if the mother doesn't deliver "on time."

Part of the reason due dates are rarely honored biologically, he explains, is because the calculations used by practitioners to set the date are flawed. Predicting a due date based on the woman's last menstrual period is simply not accurate, he says. "How often does conception occur exactly 14 days to the minute after the first drop of menstrual blood appeared?"

Moreover, argues Katz, there is too much variability among women to apply one standard time frame for all. While the mother of twins could deliver in 38 weeks, an expecting mothers with diabetes or hypertension could also expect to deliver earlier than the standard 40 weeks.

Let Biology Take Its Course

Katz's solution to satisfy the societal and emotional expectations for a specific date of delivery is to supplant the concept of due date with a new time measurement, the assigned week of delivery. An assigned delivery week, argues Katz, "will be helpful for all parties concerned," and would still allow the patient to plan for the delivery.

"An assigned week of delivery may allow women to be calmer," says Dr. Benjamin Sachs, a Harvard professor and chairman of the department of obstetrics and gynecology at Beth Israel Deaconess Medical Center in Boston.

Sachs points out that rates of inducing labor in the United Sates have "skyrocketed because of the due date issue." But assigning a week of delivery may even do more than calming nerves, says Sachs. "It may allow biology to take its course a bit more."

Some obstetricians applaud the idea of doing away with the due date. While they acknowledge the family's need to know a date for planning purposes (in-laws coming into town, maternal or paternal leaves from work), eliminating a precise due date will likely improve patient/physician relations as well as ease patient anxiety over a late delivery.

"Women even two days over their due date become very frustrated," says Dr. John G. Gianopoulos, professor and chairman of the department of obstetrics and gynecology at Loyola University Chicago Stritch School of Medicine. "They don't understand why they would miss their due date. They say, 'But that's my due date, why haven't I gone into labor'"

Experts say that vast differences in the perceptions of due date between patient and practitioner are part of the reason the concept is so problematic. While the physician thinks of the baby's debut in terms of the estimated gestational age — based on milestones such as menstrual cycles, ultrasound size and other obstetric markers — the patient applies a much more precise meaning.

"Patients are fixated on the due date," says Dr. Mary Lake Polan, professor and chair of the department of gynecology and obstetrics at Stanford University School of Medicine. "It's an emotional situation. They want to know when the baby is coming."