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Induction for "Postdue" Pregnancy

Inducing based on dates rather than indications of fetal well-being

 

Adapted from lectures by Sara Wickham, CNM

 

 

An informed decision about induction for a "postdates" pregnancy includes knowing the difference between dating the pregnancy vs. postmaturity syndrome in an infant.

 

Naegele’s Rule is currently used for calculating a woman’s“estimated date of confinement”(EDC). The Rule states that gestation lasts 280 days from the FIRST day of the LMP (266 days from assumed ovulation) for a primipara (first delivery) - and five days less for a multipara (2nd or more delivery). 

 

Naegele’s Rule ASSUMES A 28 DAY CYCLE WITH OVULATION ON DAY 14.  

 

Another method of calculation is Nichol’s Rule: gestation lasts 274 days from assumed ovulation, or counting from the LAST day of LMP, not the first (4-8 days difference - this gives leeway for length of menstrual period also!)

 

To be accurate, we would need the previous year’s calendar, with the average length of her cycle, AND the number of days in each month, AND knowing when she ovulated, AND to consider if she is a primipara or multipara. We may end up adding 8-10 days to the Naegele EDC; up to 18 days for a multipara. If she has a one year calendar of her cycle, add one day to the EDC for every day that was over 28 day cycle. Subtract one day for every day less than 28 day cycle. Ovulation lasts several days, sperm can live for several days, so conception itself carries at least a 3-4 day leeway even with one act of intercourse.

 

The above data shows us a potential 2 week margin of error in due date calculation. Nobody can say for sure the number of weeks the pregnancy is. Estimating EDCs should be a composite of all factors: size of uterus in first trimester, time of first quickening, time first heard fetal heart tones (all harder with obesity), fundal height. Sonograms can have a 2 week margin of error. We should encourage women to say mid-April, not April 15.

 

Postdue” or “postdates” refers to time passed after 40 weeks gestation.

 

EVIDENCE SUGGESTS THAT MOST “POSTDATES” PREGNANCIES ARE MISDATED.

 

THE LABOR INDUCED ONLY FOR A “POSTDATES” PREGNANCY IS GOING TO BE LONGER AND FOUR TIMES MORE LIKELY TO END IN CESAREAN SECTION.

 

Postmature” or postmaturity syndrome occurs in approximately 25% of truly postdates pregnancies and is most likely due to decreasing uteroplacental function. 

Postmaturity syndrome can only be diagnosed after delivery. It is a postdates pregnancy accompanied by a combination of the following:

 

1. Oligohydramnios; 

2. Meconium; 

3. Newborn with: loss of subcutaneous fat; long fingernails; wrinkled, peeling skin; alert; absence of lanugo; absence of vernix

 

These babies are stressed, sometimes having respiratory distress, hypoglycemia, polycythemia, and temperature instability. Meconium aspiration is a real danger.

 

The major difficulty in the management of a postdates pregnancy is determining whether postmaturity syndrome is also present. Of critical importance in an accurate dating, based on accurate data from the first and subsequent prenatal visits (“size-dates discrepancy” issues, etc).

 

15% (15 out of 100 but difficult to know which ones) of pregnancies go postdates (over 40 weeks). 15-25% of those will be postmature. About 15% of THOSE will have trouble. This is 1-2 of every 100 truly postdates pregnancies.

 

ATTEMPTING TO DATE THE PREGNANCY IS LESS EFFICIENT THAN CHECKING THE BABY BEFORE AND DURING LABOR. Fetal evaluation is an appropriate method of differentiating which fetus is at risk for problems associated with post maturity that need intervention. 

 

Once a woman has passed her due date, we monitor the pregnancy for signs of uteroplacental insufficiency and a compromised fetus. Evaluation consists of: 

 

1. Fetal movement record; 

2. Nonstress testing;   

3. Contraction stress test (checks fetus reaction to contractions through oxytocin or nipple stimulation)

4. Amniotic fluid volume. Oligohydramnios may occur because of a decreased urine production by a fetus that is chronically stressed from UPI.

5. Maternal weight. Weight loss may indicate developing postmaturity syndrome (less AFI, less fetal fat). Postdates babies are large babies + maternal weight gain. Postmature babies are small + maternal weight loss.

6. Biophysical profile, including grading of placenta.

 

Expectant management (“watch and wait”) is appropriate when all parameters are normal. These women also need extra emotional support.

 

The best indicator of fetal well-being is fetal movement By the 34th week, she should count 10 movements in less than 2 hours. Or she can observe the baby’s regular pattern and watch for increases, decreases or drastic changes. Babies do not move less closer to term. Only postmature babies stop moving because they’re worn out from using their reserves (placenta, fatty layer of body). WE CAN NEVER KNOW IF THE PREGNANCY IS POSTDUE SO WE SHOULD ASSESS POSTMATURITY BASED ON THE BABY.

 

HIGH RISK FACTORS that justify induction: diabetes; IUGR; anemia; pre-eclampsia; abnormal NST (possible cord compression); abnormal fetal movement chart; fetal arrhythmia; if you can say with assurance, oligohydramnios (hard to prove)

 

THERE IS NO EVIDENCE THAT ROUTINE INDUCTION, AT ANY GESTATIONAL AGE, IMPROVES PERINATAL OUTCOMES

 

 

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