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By John C. Hobbins, MD
In this feature, Dr. Hobbins offers a quick summary and commentary on some recently published studies.
I. False-Positive "One-Hour" Glucose Screens are Associated with Higher Rates of Perinatal Complications than Negative Screens
In a previous OB/GYN Clinical Alert, I alluded to a study indicating that a normal 3-hour glucose tolerance test does not confer upon a patient with a positive 1-hour glucose screen a major lessening of chances of macrosomia. Now there is a study that shows higher rates of shoulder dystocia (OR = 2.85), endometritis (OR = 2.18), as well as macrosomia (OR = 3.66) than in those patients with negative 1-hour glucose screens. There also was a trend toward higher rates of cesarean section and antenatal death. The composite adverse perinatal outcome was substantially higher than in patients with normal screens (OR = 5.96).
All of these statistically significant increases in risk can be related in one way or another to macrosomia. In a recent OB/GYN Clinical Alert, a study (Greco et al) was featured in which scrupulously controlled insulin-requiring diabetics were still found to have a high rate of macrosomia, indicating that there was more to excessive birth weight than maternal glucose levels alone.
After writing that piece, I was alerted by a very savvy colleague in internal medicine to an investigation in progress suggesting that in some patients glucose crosses the placenta even faster than expected. While this interesting phenomenon helps to normalize maternal blood sugars, it could elevate fetal blood glucose levels and stimulate a compensatory fetal release of insulin—the probable culprit in excessive fetal growth.
Unfortunately, while helping to explain why macrosomia continues to happen in well-controlled diabetics and, perhaps, in those with a "false positive" glucose screen, it does not aid us in fashioning a strategy to prevent it.
II. Don’t be Mislead by the Short Take
While skimming through the table of contents in the January 2004 Obstetrics & Gynecology, I came across a paper by Caughey et al entitled "Complications of Term Pregnancies Beyond 37 Weeks of Gestation." Under this title was the message: "Rates of meconium, macrosomia, chorioamnionitis, endomyometritis, and intrauterine death all increase before 42 weeks of gestation."
At first glance, one might conclude that all of these problems increased after 37 weeks. Actually, the study indicates that macrosomia and presence of meconium at delivery occur beyond 38 weeks, that operative delivery and chorioamnionitis occur more often after 40 weeks, and that rates of intrauterine demise rise only after 41 weeks.
From the summary, one might surmise that Mother Nature should have arranged things so that most patients would go into labor by 37 weeks, thereby circumventing all of these nasty problems. In fact, in the discussion section Caughey et al suggest that "given our data, it might be found that the balance of risks and benefits from intervention in low-risk pregnancies should be earlier than current management."
First, there is evidence in the literature that intervening prior to term in patients known to have macrosomic fetuses does not improve outcome or decrease cesarean rates. Second, even when meconium is present, the risk of severe meconium aspiration is rare, and when it does happen, there is a strong suggestion pathologically that the process is chronic rather than acute. In essence, in these patients the meconium is a symptom of trouble, not the cause. Third, the intrauterine demise data in the paper shows an increase only after 41 weeks (OR = 2.6; CI, 7.29). However, the actual percentage of demised fetuses in each age group is not mentioned, nor are we told how many of these had 21st century fetal surveillance.
Inductions are intrusive for some patients and are far from innocuous with regard to morbidity. They require more nursing attention and are darn expensive. Therefore, from now on I would suggest holding the pitocin in patients who have no risk factor other than having succeeded in avoiding a preterm delivery.
III. More Information Regarding Single vs Double Layer Closure of the Uterus During Cesarean Section
In a previous special feature on the technical aspects of cesarean section, the methods of uterine closure were touched upon briefly. A study from Montreal (Bujold E, et al. Am J Obstet Gynecol. 2002;186:1326-1330) suggested that single layer closure was associated with a higher rate of uterine rupture in a subsequent pregnancy. In the January 2004 American Journal of Obstetrics & Gynecology, a paper emerged in which the authors tracked pregnancies after uteri were closed in the previous pregnancies with either single or double layers. The study was not randomized (nor was the Montreal study). These authors found no difference in the number of uterine ruptures, but less blood loss, shorter operative times, and less endometritis in the single-layer closure group. However, there were more uterine windows noted in those with single-layer closure who needed a subsequent cesarean section.
The authors thought that the possible reasons for the discrepant results between their study and the Montreal study was that they used a nonlocking vicryl suture compared with a locking chromic suture used in Montreal. The authors postulated that a locking stitch predisposes toward tissue ischemia, and chromic has less "staying power" than vicryl. I suppose we will all have to wait for the ultimate randomized trial to get the final answer, but there seems to be no reason at this point to switch back to a double-layer closure.
1. Greco P, et al. Fetal Diagn Ther. 2003;18:437-441.
2. Stamilio DM, et al. Obstet Gynecol. 2004;103:148-149.
3. Caughey AB, Musci T. Obstet Gynecol. 2004;103:57-62.
4. Durnwald C, Mercer B. Am J Obstet Gynecol. 2003; 189(4):925-929.
5. Bujold E, et al. Am J Obstet Gynecol. 2002;186(6): 1326-1330.