What's the deal with the 42-week cutoff?

[pollyanna123]

My first two kids came at 41+2 and 40, but my current pregnancy is at 41+3 and counting....

If I get to Tuesday, dh and I will have to decide whether to continue past 42 weeks or ditch our planned homebirth and be induced in the hospital. My midwife is okay with going past 42 weeks. The perinatologist I saw this morning for my BPP said his personal cutoff is 42 weeks.

Can you help us get started on our research? 42 weeks seems to be a very common cutoff in the medical community, even amongst midwives. Why? What are the statistics on this? 

[blessedwithboys]

Don't have stats for you but my kids came at 42 wks and 42+3 and were perfectly healthy.  If I had had a MW who was cool with going past 42 wks I may have avoided a totally unneccesary csec!  Personally, if I was in your shoes, if all was good and healthy, I would keep planning a HB.

[mckittre]

My first came at 40+3, and second at 42+1, so I did a lot of agonizing over this too.  The midwives where I was usually used 42 weeks as their recommendation as well, but weren't firm on it. 

One thing to remember is that all cutoffs are arbitrary, and part of the reason it's "42 weeks" is that the statistics are only taken weekly.  So when a study sees an increase in bad outcomes "after 42 weeks", babies born at 42+0 and 42+6 are lumped into the same category, while babies at 41+6 and 42+0 are in different categories. 

Everything I read suggested that there is a small increase in bad outcomes as the pregnancy goes later.  Very small on an individual scale, large enough in a statistical sense for doctors/midwives to pay attention.  However, some of those negative outcomes are not caused by being late, they're preexisting (and may be causing the delay in labor). 

I decided the risks were small enough that I was comfortable playing it by ear (I did get the recommended NSTs and BPPs and passed with flying colors).  By the time I hit 42 weeks, I had lots of prelabor, and she was born a day later. 

Interestingly, despite the fact that the pregnancy was dated by early ultrasound (11 weeks), my baby came out looking just like a 40 weeker, according to the midwife.  Still had vernix, placenta was beautiful with no calcification, no meconium, no wrinkled skin or long nails, etc...  She was nearly 10 lbs, though.

If it were me, I'd go on intuition, symptoms, any test results, etc... rather than an arbitrary cutoff.  And I suspect I'd have worried a bit more if I'd started getting close to 43 weeks.

[mwherbs]

Acta Obstet Gynecol Scand. 2011 Jan;90(1):26-32. doi: 10.1111/j.1600-0412.2010.01019.x. Epub 2010 Nov 26.
Significant effects on neonatal morbidity and mortality after regional change in management of post-term pregnancy.
Grunewald C, Håkansson S, Saltvedt S, Källén K.

Department of Clinical Science and Education, Södersjukhuset, Karolinska Institute, Stockholm Department of Pediatrics, Umeå University Hospital, Umeå Centre of Reproduction Epidemiology, University of Lund, Lund, Sweden.

Their calculations were about 20% of pregnancies were >=42 weeks +2, but in more recent years they increased induction rates so the % dropped to around 6% with a 50% mortality decrease

[wombatclay]

The really short reply is that the "average length" of the "average pregnancy" should form a happy little bell curve covering 37/38 to 41/42 weeks (with 39/40 weeks being the middle of the curve).  And many studies show that babies tend to have problems if they are born too far off either edge (pre-37 or post-42).  Of course, as medical technology advances, the chances for a happy outcome "pre-37" have gotten better but nothing much has changed at the "post-42" end of the scale other than monitoring tools (NST for example) and the ability to "hurry up" a babe that is taking it's time to prevent them from falling off that bell curve.

As medical technology advances, so does legal "technology" and since it's easier to blame someone for what they "should have done but didn't" than it is to blame them for "unforeseen complication resulting from common intevention they did do"... well, turning 42 (or 41, or 40) weeks into a sort of pregnancy limit ignores all those women/babes who would normally fall into the 40 to 42 week part of the curve and introduces all the problems of induction BUT it also protects a provider or facility from being "blamed" for a poor outcome that could, maybe, have been avoided by an earlier birth.

More papers:

Journal of Perinat Med 2010 Mar;38(2):111-9. Guidelines for the management of postterm pregnancy

---basically they find that inductions are risky and going postterm is risky so women should be given information about both so they can give informed consent for the option they feel most comfortable with.

Matern Fetal neonatal Med 2002 Jan;11(1):50-3. Post-term pregnancy: should induction of labor be considered before 42 weeks?

--they reviewed thousands of "low risk" births and found that the closer you got to 42 weeks and then the further past 42 weeks you went, the greater the risk for specific complications (macrosomia, c/s, and non-progressive labor for the most part).  Their conclusion is that induction should be considered.

Am Fam Physician 2005 May 15;71(10):1935-41. Management of pregnancy beyond 40 weeks' gestation

--falls on the other side, prefering to watch and wait in otherwise low risk pregnancies

Am J Obstet Gynecol 2010 Dec;203(6):554.e1-8. Epub 2010 Aug 30. Impact of maternal age on fetal death: does length of gestation matter?

--found that in older moms (40+ specifically) risks of fetal death climbed after 42 weeks so this could indicate the need for closer monitoring or induction

J Midwifery Womens Health 2009 Sep-Oct;54(5):351-6. Comparison of induction of labour and expectant management in postterm pregnancy: a matched cohort study

--found that induction resulted in roughly the same number of c/s as "watch/wait" in pregnancy past 42 weeks, but that the "watch/wait" group had more birth complications than the induced group so recommends that induction be offered to all women at 42 weeks.

There are more studies of course, and there are an equal number of papers/studies that report the risks of inductions, early term cesareans, and iatrogenic pre-term deliveries.  So it's a complicated discussion with many factors specific to an individual woman in an individual pregnancy and so it usually gets ignored in favor of the easy "one size fits all" of a 42 week limit.

[mandib50]

research does indicate more negative outcomes for pregnancies beyond 42 weeks, but there are many factors a midwife would want to consider before issuing an ultimatum about cut off dates for postdates. in a culture of litigation and not trusting women's bodies, i think that is why doctors/OB's etc don't consider the entire picture of an individual client and prefer to make decisions based on a black/white way of thinking.

[pollyanna123]

Thanks everybody. In a couple of hours, I'll be 41+6. I'll be having a big discussion with my midwife tomorrow morning. I had an NST/BPP on Friday with a perinatologist that went very well. so that was reassuring. I know my midwife takes these things on a case-by-case basis and is fine with going past 42 weeks, but I don't know how far past 42 weeks. 

[MegBoz]

Quote:

Originally Posted by mckittre 

Everything I read suggested that there is a small increase in bad outcomes as the pregnancy goes later.  Very small on an individual scale, large enough in a statistical sense for doctors/midwives to pay attention.  However, some of those negative outcomes are not caused by being late, they're preexisting (and may be causing the delay in labor). 

I decided the risks were small enough that I was comfortable playing it by ear (I did get the recommended NSTs and BPPs and passed with flying colors).  By the time I hit 42 weeks, I had lots of prelabor, and she was born a day later. 

<snip>

If it were me, I'd go on intuition, symptoms, any test results, etc... rather than an arbitrary cutoff.  And I suspect I'd have worried a bit more if I'd started getting close to 43 weeks.

Great post overall & I totally agree. (I went to 41W4D with my DS, decided to have my membranes stripped & that kicked off labor 2 hours later. But I had not yet scheduled the induction for 42W0D. & that was a planned hospital birth anyway!) If I go to about 41W5D again, I will definitely try regular membrane stripping again. Research is slightly mixed on whether it shortens pregnancy & reduces the number of post-dates pregnancies, but risks of it are so low anyway I think it's worth trying.

The book, 'Gentle Birth Gentle Mothering" by Dr. Sarah Buckley has some great info on post-dates too. It was published in 2009, so it's quite current.

I also think Wombatclay's point about "it's easier to blame someone for what they "should have done but didn't"" is important to note & certainly contributes to common hospital policy to not "allow" any pregnancy to continue beyond 42W. I think when you bear that fact in mind, it's easier to understand why that is policy, even though it's not necessarily so crazy, risky, dangerous to go beyond 42W! As someone else said, 3 weeks BEFORE a due date is still considered fine & within the range of normal, but over 2 weeks AFTER a due date is not?