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The Implications of a Prolonged Pregnancy

Thursday, March 7th, 2013

You’ve waited nine long and painful months. Your ankles are swollen, your mood swings are drastic, and your belly feels like it’s about ready to burst. When your due date comes and goes without those telltale contractions, it’s impossible for you not to get a little upset.

However, your doctor or midwife most likely gave you the midpoint of your due month, i. e., 40 weeks (280 days of gestation).  Actually, your baby is considered mature between 38 weeks and 42 weeks (266 days to 294 days of gestation).  A prolonged pregnancy is any pregnancy that lasts beyond 294 days or 42 weeks.  I know you didn’t want to hear that, but that’s the truth.  I did my post-doctoral thesis at Columbia on postterm pregnancies and we had mothers pregnant up to 44 weeks.  While it seems like a really long time, it’s actually more common than you might think. No one actually knows why a pregnancy is prolonged.   There are many theories, but no one has found the reason for a pregnancy going beyond 42 weeks, except in cases of anencephaly.

There is nothing abnormal about a pregnancy going beyond 40 weeks, even to 42 weeks. The best way to ensure that your pregnancy lasts the normal 38 to 42 weeks is to stay healthy and active. Maintaining a healthy weight and avoiding harmful chemicals such as caffeine and alcohol will help you ensure that your pregnancy is as normal as possible.  If that doesn’t work though, thanks to advances in modern technology and medicine, there are a few different options for women with prolonged pregnancies. After a pregnancy reaches the midpoint of term, i.e., 40 weeks, your obstetrician may want to test the baby for its well being with electronic fetal surveillance.  Changes occur after 41 weeks that may jeopardize the baby’s health if not closely monitored.  If mom’s perception of fetal movement is normal, i.e. at least four kicks in one hour, and the testing is normal, it is best to wait for Mother Nature to bring on labor naturally.  However, if your physician or midwife has evidence that your baby may be in jeopardy, he or she will choose to induce your labor.

Stillbirth is a concern at any time during the pregnancy, but especially after 42 weeks. The amniotic fluid around the baby peaks at  34 weeks and decreases as the pregnancy progresses to term.  That is the reason for monitoring and assessment of the fluid when the pregnancy has passed 40 weeks.  The American College of Obstetricians and Gynecologists still defines postterm (prolonged) pregnancy as one extending beyond 42 weeks——not 40 weeks and not 41 weeks.  Babies also gain weight in utero with each passing week, so the longer baby is in “the oven” the bigger it will become (but not by much) until it reaches a critical size and then its weight begins to decline.  A mother need not worry about delivering a Butterball turkey, if she continues to normally gain ½ to one pound per week.  Few babies born after their due date experience any real issues,

Much of pregnancy is up to chance. Once you conceive, the pregnancy is really on “automatic pilot”.  From the time of conception to the time of delivery, the outcome of your pregnancy depends on your particular body and the way the hormones are interacting. The word, “obstetrics” means to “stand by”.  Therefore, inducing labor in normal pregnancy before 42 weeks violates our very creed.  That’s the fun of being pregnant.  It’s up to Mother Nature.  Some women may deliver at 38 weeks (which is normal for a term pregnancy), while others may deliver at 42 weeks (which is also normal).  Both of my children were delivered beyond 42 weeks and both are Ivy-league graduates and totally healthy.

Try not to fret or force your doctor or midwife into inducing labor, which may not have been in the cards (or the best interest of your baby), only for you to end up with a cesarean birth rather than a natural one.

 – Yvonne S. Thornton, M. D., M. P. H.