Anyone who has ever been pregnant, had a child, or is over the age of ten knows that a woman is “due” to have her baby at 40 weeks, or more commonly, 9 months. The history of calculating a woman’s due date in modern times goes back to the mid-1800s. A German obstetrician named Franz Karl Naegele devised a rule to calculate the expected date of delivery as the following: From the first day of the woman's last menstrual period (LMP) by adding 1 year, subtracting three months and adding seven days to that date. The result is approximately 280 days (40 weeks) from the LMP. The first major error with this method of calculating is that not every woman ovulates on the same day, and this rule fails to take that into account.
Another method, albeit much less popular and rarely used by medical caregivers, is one called Parikh’s formula. This one does take into account the length of a woman’s cycles, therefore also taking into account possible variations in ovulation, and is written as such: adding 9 months to LMP, subtracting 21 days, then adding duration of previous cycles. This method would obviously be a more accurate way to calculate an estimated due date, but for the sake of having a standard calculation most medical providers use the same calculation for all women regardless of if the date of conception is known by the woman. These calculations place a woman’s due date at 280 days after her last menstrual period.
Why all the controversy over due dates? Why not simply let women go into labour naturally when the baby and her body are ready? We know that even the Doctors who devised methods of calculating due dates used them simply as estimated delivery dates. Large studies have shown that there is a standard deviation of 13 days from the due date, meaning that 90% of women will give birth within 3 weeks of the due date- in either direction, not only earlier than but later as well. [i] In a study quoted often by Henci Goer, white women having their first babies carried, on average, 8 days past their due dates.[ii] With the research showing that women carry babies for different lengths of time depending on age, race, or number of pregnancies, among other factors, why do many caregivers insist on induction at 41 weeks- which is one day less than the average for white first time moms, or in some cases, begin planning an induction before a woman has even reached her due date?
Another issue that needs to be addressed is the accuracy of due date calculation. Because of the variations in women’s cycles, and therefore the range of possible days of ovulation within even a similar cycle length, delayed ovulation can be a factor in what is thought to be a post-term pregnancy. The SOCG recommends first trimester ultrasound in order to properly date a pregnancy. Most pregnancies induced after 41+0 weeks are found not to be > 41+0 when an early ultrasound rather than LMP is used to date the pregnancy.[iii] Of course, to those who wish to avoid ultrasounds, the most precise due date is usually calculated by the woman who tracks her cycles, understands the signs of ovulation, and can therefore be most accurate in dating her own baby’s conception.
Both the WHO and the ACOG define a post-dates pregnancy as one that has extended to or beyond 42 weeks (294 days). According to the ACOG the health risks for mother and baby increase as the pregnancy is prolonged. The risks of a pregnancy that passes 42 weeks can include (but are not limited to): low amniotic fluid, placental dysfunction, meconium aspiration, profound mental retardation (PMR), and stillbirth. Many of these risks have been found in studies that have not excluded high-risk pregnancies or fetuses with known congenital anomalies. In studies that excluded these risk factors, there was no increase in PMR found in post-term infants, although there is still an increased risk of stillbirth for pregnancies that are prolonged, that is, longer than 42 weeks. [iv] A homebirth doctor in Australia, Dr. John Stevenson, maintains that in 106 true post-dates babies only one baby showed distinct signs of post-maturity.[v] Conclusions can be drawn from his experience that all babies mature at different rates, just like all women enter puberty or menopause at different rates. Growth and maturity cannot be measured with an exact science at any stage of life.
The likelihood, with our current medical protocols, of a woman being “allowed” to carry her baby past 42 weeks while being followed by an Obstetrician or Midwife in Quebec is unlikely. A registered midwife is required to transfer care at 42 weeks, so a woman wishing for a birth center or home birth will be forced to give birth at a hospital. A woman with a standard GP or OBGYN will, in most cases, follow her doctors orders for non-stress tests and ultrasounds, where questions may potentially be raised about the size of the baby, or the level of amniotic fluid, or worse- her own physique will be critiqued and her body deemed unable to properly deliver her baby. Many women will be faced with the decision to stay for an induction or a c-section and if they choose to leave the hospital may even be told they are putting their baby at risk of dying if they do so.
What some caregivers fail to mention are the serious risks involved in an induction. We know that caesarean rates rise for induced births[vi], as well as the majority needing to be induced with chemical methods and/or by breaking the bag of waters artificially. There is a certain level of interference with the natural process of birth during an induction. Of course, there are always cases when an induction is the obvious choice and will lead to the best possible outcome. But with up to 45% of women having some method of induction introduced to their birth[vii], we know there is a misuse of this intervention.
Having personally endured the countdown (my own included) of when my pregnancy would finally be over with my due date arriving and then quickly passing by without a birth being involved, I understand what many women are feeling. It’s definitely not easy to feel the rising amount of pressure on your body’s performance. Some women feel that their bodies have begun to fail them, even before they get to the starting line of labour. Others feel that they are being inconvenient or unaccommodating to the family or friends who have made themselves available for the week or so surrounding the impeding birth. Still, there are others who simply don’t want to pregnant any longer. At 41 weeks it’s much harder to be comfortable with waiting for the baby to arrive “when it’s time”. A woman who believed her due date was only a suggestion when she was 15 weeks might not be feeling the same way at this point. Women get DESPERATE. Some are willing to try anything: walking, spicy food, acupuncture, sex, herbal teas, castor oil, homeopathy, bumpy car rides, and evening primrose oil are just a few tried and true methods for a more natural induction.
With the experience of one pregnancy and birth behind me, I personally plan on adding 5 days to my own calculated due date for any subsequent pregnancies. I recommend to some women to not specify the exact date they are “due” to family or friends. It can be quite stressful, without reason, for many women. The last few weeks of pregnancy should be spent enjoying the final moments before the new baby, getting a few mornings of extra sleep, putting up your feet, and going out for a date night with friends or your partner. It should NOT be about being stressed out with extra doctors appointments, or increasing the risks of interventions at a birth that may not have needed them.
As with any other proposed intervention, the choice to eschew the due date or begin labour with an induction once passed a certain point of pregnancy is an individual choice. And it isn’t always as clear as some would think. Every woman deserves to make an informed choice that she can be comfortable with.
[i] Bergsjø P, Denman DW 3rd, Hoffman HJ, Meirik O. (1990). "Duration of human singleton pregnancy. A population-based study.". Acta Obstet Gynecol Scand: 197–207.
[ii] Mittendorf R et al. The length of uncomplicated human gestation. Obstet Gynecol 1990;75(6):929-32
[iii] http://www.sogc.org/guidelines/documents/gui214CPG0809.pdf
[iv] http://www.acog.org/publications/faq/faq069.cfm
[v] http://newlifebirth.com/induction.html
[vi] http://www.medicalnewstoday.com/releases/98156.php
[vii] http://www.sogc.org/journalismawards/InductionOverload.pdf
Another method, albeit much less popular and rarely used by medical caregivers, is one called Parikh’s formula. This one does take into account the length of a woman’s cycles, therefore also taking into account possible variations in ovulation, and is written as such: adding 9 months to LMP, subtracting 21 days, then adding duration of previous cycles. This method would obviously be a more accurate way to calculate an estimated due date, but for the sake of having a standard calculation most medical providers use the same calculation for all women regardless of if the date of conception is known by the woman. These calculations place a woman’s due date at 280 days after her last menstrual period.
Why all the controversy over due dates? Why not simply let women go into labour naturally when the baby and her body are ready? We know that even the Doctors who devised methods of calculating due dates used them simply as estimated delivery dates. Large studies have shown that there is a standard deviation of 13 days from the due date, meaning that 90% of women will give birth within 3 weeks of the due date- in either direction, not only earlier than but later as well. [i] In a study quoted often by Henci Goer, white women having their first babies carried, on average, 8 days past their due dates.[ii] With the research showing that women carry babies for different lengths of time depending on age, race, or number of pregnancies, among other factors, why do many caregivers insist on induction at 41 weeks- which is one day less than the average for white first time moms, or in some cases, begin planning an induction before a woman has even reached her due date?
Another issue that needs to be addressed is the accuracy of due date calculation. Because of the variations in women’s cycles, and therefore the range of possible days of ovulation within even a similar cycle length, delayed ovulation can be a factor in what is thought to be a post-term pregnancy. The SOCG recommends first trimester ultrasound in order to properly date a pregnancy. Most pregnancies induced after 41+0 weeks are found not to be > 41+0 when an early ultrasound rather than LMP is used to date the pregnancy.[iii] Of course, to those who wish to avoid ultrasounds, the most precise due date is usually calculated by the woman who tracks her cycles, understands the signs of ovulation, and can therefore be most accurate in dating her own baby’s conception.
Both the WHO and the ACOG define a post-dates pregnancy as one that has extended to or beyond 42 weeks (294 days). According to the ACOG the health risks for mother and baby increase as the pregnancy is prolonged. The risks of a pregnancy that passes 42 weeks can include (but are not limited to): low amniotic fluid, placental dysfunction, meconium aspiration, profound mental retardation (PMR), and stillbirth. Many of these risks have been found in studies that have not excluded high-risk pregnancies or fetuses with known congenital anomalies. In studies that excluded these risk factors, there was no increase in PMR found in post-term infants, although there is still an increased risk of stillbirth for pregnancies that are prolonged, that is, longer than 42 weeks. [iv] A homebirth doctor in Australia, Dr. John Stevenson, maintains that in 106 true post-dates babies only one baby showed distinct signs of post-maturity.[v] Conclusions can be drawn from his experience that all babies mature at different rates, just like all women enter puberty or menopause at different rates. Growth and maturity cannot be measured with an exact science at any stage of life.
The likelihood, with our current medical protocols, of a woman being “allowed” to carry her baby past 42 weeks while being followed by an Obstetrician or Midwife in Quebec is unlikely. A registered midwife is required to transfer care at 42 weeks, so a woman wishing for a birth center or home birth will be forced to give birth at a hospital. A woman with a standard GP or OBGYN will, in most cases, follow her doctors orders for non-stress tests and ultrasounds, where questions may potentially be raised about the size of the baby, or the level of amniotic fluid, or worse- her own physique will be critiqued and her body deemed unable to properly deliver her baby. Many women will be faced with the decision to stay for an induction or a c-section and if they choose to leave the hospital may even be told they are putting their baby at risk of dying if they do so.
What some caregivers fail to mention are the serious risks involved in an induction. We know that caesarean rates rise for induced births[vi], as well as the majority needing to be induced with chemical methods and/or by breaking the bag of waters artificially. There is a certain level of interference with the natural process of birth during an induction. Of course, there are always cases when an induction is the obvious choice and will lead to the best possible outcome. But with up to 45% of women having some method of induction introduced to their birth[vii], we know there is a misuse of this intervention.
Having personally endured the countdown (my own included) of when my pregnancy would finally be over with my due date arriving and then quickly passing by without a birth being involved, I understand what many women are feeling. It’s definitely not easy to feel the rising amount of pressure on your body’s performance. Some women feel that their bodies have begun to fail them, even before they get to the starting line of labour. Others feel that they are being inconvenient or unaccommodating to the family or friends who have made themselves available for the week or so surrounding the impeding birth. Still, there are others who simply don’t want to pregnant any longer. At 41 weeks it’s much harder to be comfortable with waiting for the baby to arrive “when it’s time”. A woman who believed her due date was only a suggestion when she was 15 weeks might not be feeling the same way at this point. Women get DESPERATE. Some are willing to try anything: walking, spicy food, acupuncture, sex, herbal teas, castor oil, homeopathy, bumpy car rides, and evening primrose oil are just a few tried and true methods for a more natural induction.
With the experience of one pregnancy and birth behind me, I personally plan on adding 5 days to my own calculated due date for any subsequent pregnancies. I recommend to some women to not specify the exact date they are “due” to family or friends. It can be quite stressful, without reason, for many women. The last few weeks of pregnancy should be spent enjoying the final moments before the new baby, getting a few mornings of extra sleep, putting up your feet, and going out for a date night with friends or your partner. It should NOT be about being stressed out with extra doctors appointments, or increasing the risks of interventions at a birth that may not have needed them.
As with any other proposed intervention, the choice to eschew the due date or begin labour with an induction once passed a certain point of pregnancy is an individual choice. And it isn’t always as clear as some would think. Every woman deserves to make an informed choice that she can be comfortable with.
[i] Bergsjø P, Denman DW 3rd, Hoffman HJ, Meirik O. (1990). "Duration of human singleton pregnancy. A population-based study.". Acta Obstet Gynecol Scand: 197–207.
[ii] Mittendorf R et al. The length of uncomplicated human gestation. Obstet Gynecol 1990;75(6):929-32
[iii] http://www.sogc.org/guidelines/documents/gui214CPG0809.pdf
[iv] http://www.acog.org/publications/faq/faq069.cfm
[v] http://newlifebirth.com/induction.html
[vi] http://www.medicalnewstoday.com/releases/98156.php
[vii] http://www.sogc.org/journalismawards/InductionOverload.pdf
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