The difference between your FRENCH and AMERICAN pregnancy due dates (Why have one when you can have two??)

Pregnancy due date Estimated delivery date

One of the first things I learned when I moved here is that the French do not readily accept the ways of English-speaking peoples. They turn their noses up at mayonnaise (quelle horreur), wonderbread (who needs wonderbread when you have baguette), and show a general disregard for the English language. Even those American traditions that have been adopted are disguised in French terms so nobody catches on: McDonalds is macdo, pronounced with perfect tonal indignation, and hamburgers are elegantly referred to as le burger (pronounced leh boorgare). So I shouldn’t have been surprised to discover that the pregnancy due date I was given in the US – April 16th – would not be accepted here, and my new given French due date would be April 24th.

Why the difference in due dates? And what difference, if any, does this make? Lets take a look at how those dates are calculated:

How to calculate your US or UK due date:

Your due date is calculated from your last menstrual cycle (LMP). You add 40 weeks (9 months and 1 week) to that date, so in effect your menstrual period and ovulation days are included as part of pregnancy, even before there is a fertilized egg. It’s a little bonus that makes you feel better about yourself when after a month of conception you are hugging the toilet, interminably nauseous, vomiting, and wondering how you are going to make it through nine months of this. But ultimately at the 40th week marker, you have only been pregnant for 38 weeks.

How to calculate your French due date:

There will be no cheating or bonuses with the French. The French start the count at your estimated date of conception (when your little miracle was conceived), and add 39 weeks (exactly 9 months) to that date. In effect that makes your due date 41 weeks after your last menstrual period, and 39 weeks after becoming pregnant.

This roughly translated to a due date that is one to two weeks later, as your obstetrician may do some mysterious calculations trying to estimate your monthly cycle length and shoots out an adjusted number, which is how I have two due dates 10 days apart from each other.

Is this difference splitting hairs or does it actually matter?

The due date is more of a temporal marker than an actual appointment: only 4% of women deliver on their actual due dates(1).  Indeed many women, and especially first time mothers will go on to deliver within the two weeks after their delivery. By 42 weeks after the last menstrual period 90% of women will have delivered. While the due date itself is not that important, receiving term appropriate prenatal care (such as genetic screening tests and gestational diabetes screening within the appropriate time frame) and identifying when a woman has progressed past a “term pregnancy” (i.e. is post-term) is. After 42 weeks there is an increased risk to the fetus (2), both in terms of death and functional impairment. Thus as long as a pregnant woman is receiving regular prenatal care by an experienced professional there should be no blaring changes in their care based on differences in the estimated delivery date.

However the difference in definitions here may lead to more subtle alterations in care. If you set your expectations for a later delivery date, both pregnant women and obstetric providers might get through the entire term period (37-42 weeks) with less anticipation and anxiety that an arbitrary deadline is upcoming and has been passed. Furthermore, the time for induction of labor is 42 weeks in France, which is closer to the French due date, whereas guidelines in the US are less specific, leaving many providers to choose to induce prior to 42 weeks of gestation and closer to the 40 week due date. The indications for inductions can vary from emergent concern for maternal and fetal safety, urgent concern for post-term dates, to semi-elective and elective reasons, but there is research suggesting that there is an increased rate of “psychosocial induction” in the United States(3). Unsurprisingly, US data has been showing an overall increase in the number of labor inductions (4). This may have unintended negative consequences as artificial inductions may lead to increased discomfort during labor and a greater need for further medical intervention. Thus at the very least, the earlier US due date may lead to more maternal anxiety once she becomes “term,” and at the worst it could theoretically mean more artificial inductions of labor leading to less maternal satisfaction and well being with the birthing process.

I hate to admit this, but perhaps the French have a slight advantage on this one? At heart I am a true American patriot, and whenever someone asks for my due date I either average the two dates out (as if spewing out a third arbitrary date makes any difference), or blurt something out about having two dates which only confuses people further. Why do the specifics of the date even matter in conversation? If as a medical professional, aware of the nuances of the system, I have still become inexplicably wed to the idea of having a specific date represent the conclusion of my pregnancy, perhaps it does suggest a neurosis of human nature that likes to place a label on a natural process, and unconsciously build up expectations around that set point. In which case we should perhaps look to the French on this to decrease our level of national anxiety surrounding an arbitrary expiration date.



  3. Trends and Issues in Labor Induction in the United States: Implications for Clinical Practice. Simpson, Kathleen Rice et al. Journal of Obstetric, Gynecologic & Neonatal Nursing , Volume 32 , Issue 6 , 767 – 779
  4. S. national trends in labor induction, 1989-1998. Zhang, J, Yancey, MK, Henderson, CE. J Reprod Med. 2002 Feb;47(2):120-4.

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